Sunday, August 28, 2011

The Worst Cars in the World

Second installment in the ongoing series

Dodge/Plymouth Neon

The Neon was seen as something fresh and new, and represented a new direction for Chrysler in the early 90’s. They were finally weeding out all of the terrible K car derivatives from the 80’s and the Neon was poised to be something to challenge the compacts from Japan that had taken over the market. This was not to be because the Neon was such a terrible car.
1995 Dodge Neon
This car really represented a step forward for Chrysler because on paper, it had all of the same things that the Japanese rivals had, but it also had some great things that the Japanese didn’t have, such as more power, and a supposed fun-to-drive factor. These were things that would draw people over from all of Chrysler’s rivals. The Neon also made domestic offerings from the same class such as the Escort and the Cavalier, look like the Pinto and the Chevette, or any of the other old bombs from the days of the AMC Gremlin.

While Neon sales were pretty good for the first few years, it didn’t take long for the auto buying public to realize that the Neon was not really much better than the old nasty K cars that it was replacing. The people who buy cars like the Japanese cars that the Neon was supposed to compete against, don’t care about a car that says “Hi” (remember the early Neon ad campaigns), and they don’t particularly care about which car has the most horsepower. They want a car that is solid to drive and requires no repairs, and very little maintenance. As it turned out the neon didn’t meet either one of these criteria, and as such the people buying cars from Honda, Toyota, and Nissan didn’t turnout.

It’s one thing to say that the Neon is bad because it seems like the check engine light is always on, but if you consider that nearly every single Neon ever sold is going to have to have the head gasket replaced at some point, it’s easy to see just how bad they are. 10 years ago during the heyday of the Neon, technicians at Chrysler, Dodge, and Plymouth dealers could literally spend all day replacing head gaskets, and boy did those people make a ton of money doing so! This is a major repair, and something that cannot be ignored. Most of the time the head gasket would leak more oil than the Exxon Valdez. If Dodge had come up with a good way to repair them and have the repair last then you might let this one mistake slide, but it was very common for a Neon to have to have the head gasket replaced more than once for this same problem.

1999 Dodge Neon
Speaking of ignoring repairs, Neon owners get used to the Check Engine light coming on and shutting off randomly, so much so that they actually convince themselves that this just normal and it doesn’t mean anything, nor is there anything that can be done about it. They are correct in a way, for a Neon, it is normal because there is always something broken or in the process of breaking. The check engine light is just an indicator that if it’s not one thing falling apart, it’s another.

Of course this is not all, the transmissions in the Neons also have a tendency to slip or to jerk or to do anything other than shift smoothly. The lucky neon owners are the few that have a Neon with a stick instead of an automatic. These junky little gear boxes are the biggest part of the car that didn’t change much from the dark days of the K cars. The Neons were not alone in this as many of the Chrysler and Dodge models from around that time period suffered from bad transmissions as well. I would say that 80% of people who have owned a Chrysler or Dodge minivan from the 80’s or 90’s, have probably had to put a transmission (or two) in the thing at some point.

Then there is the interior. They were so cheap and junky that none of the parts fit together or stayed together. The cars all came equipped with a stereo which was needed so you could turn up the music and drown out all of the squeaks and rattles. Because the Neon is an entry level car people think that this poor quality in the interior is okay or normal. Just because a car is inexpensive doesn’t mean that it’s okay for it to fall apart. Young people who are hard on their cars often end up driving these things and their lack of proper care for the vehicle only makes the interior that much worse.
2005 Neon. The final look
The Neon was first released in 1994. Do you ever see any of these old Neons on the road anymore? Not really, probably because they have all died. This is always a good test for giving you a general idea about whether a car is good or not. The original Neons sold very well but they are a rare sight on today’s roads. Like so many other cars from the struggling big three, the Neon was a hit and great step in the right direction, but as soon as sales begin to slump, the company just abandons the model altogether rather than continue to develop it in a manner that would hold interest and maintain sales. I could name 50 cars that have suffered the same fate. They might make a few token changes to the exterior but it requires more than this to regain the interest of the buying public. The neon had two minor updates before it was discontinued in 2005, and honestly many of the early problems were remedied in some form or another. These efforts were all a day late and a dollar short. The Neon will forever be remembered as a terrible car, and those who say otherwise usually just don’t understand.
Put a turbo on it and call it an SRT-4 but it's still just a Neon.
 Other posts about The Worst Cars in the World

Thursday, August 25, 2011

What Does Octane Mean?

87, 89, 91. If you live in the Rocky Mountain region then you will see 85, 87, and 91. These are your choices when you pull up to the gas pump. These are the various octane ratings of the fuel that the gas station is selling, and as far as most people are concerned the only difference between any of them is typically $.10 per gallon. The truth is there are more important differences besides the price but it has nothing to do with the quality of the fuel, or the amount of power the fuel will produce.
Choices, choices, choices

The octane rating refers to ability of the fuel to resist combustion until the spark is introduced into the combustion chamber. You might also say that it is somewhat of a reflection of how much octane is blended with how much heptane to produce the fuel. In order to understand the difference between octane and heptane we should have a brief look at hydrocarbon chains. A hydrocarbon is a molecule that is made up of hydrogen and carbon.

The first of all the hydrocarbon chains, or molecules, is CH4, otherwise known as methane. This is the fuel that is used to heat houses and other buildings along with running your gas stove. Methane is made from a single carbon atom surrounded by 4 hydrogen atoms. After methane comes ethane, C2H6, then propane, C3H8, then butane, C4H10, then pentane, hexane, heptane, and octane.
Octane molecule

With each successive hydrocarbon an extra carbon is added along with two more hydrogens. The small hydrocarbons are in a gaseous form at room temperature and at a normal atmospheric pressure. Starting with pentane they become liquid at room temperature but they are very volatile and vaporize quickly. As the molecules get bigger they are still liquid but they loose their volatility and do not evaporate. For example, diesel fuel is usually made up of hydrocarbon chains somewhere in the neighborhood of C14H36. If you spill a bit of gasoline it evaporates quickly, but if you spill a bit of diesel fuel it will sit there until you wipe it up. C48H98 and other similar molecules that are very long are actually polymer chains more commonly known as plastic. This obviously, will not evaporate either.

So getting back to heptane, and octane, and the numbers on the gas pump. Heptane is cheaper than octane, but octane is better at resisting detonation. Detonation, also known as knocking or pinging, and related to pre-ignition, is a condition where the air/fuel mixture burns before the spark is introduced. This happens when something causes an excessive build up of heat in the combustion chamber and that heat lights off the fuel before the spark gets there. When this happens, the piston is not in the proper position to turn the force of the rapidly expanding air, into movement of the crankshaft. Imagine a piston moving upward in the cylinder with great force and then being pushed back against itself violently by this sudden explosion. This leads to severe engine damage if it happens too much. With normal combustion, the piston is on its way down when the fuel burns, it must not be still moving up.

The greater the percentage of octane in the fuel the more it resists detonation. The number 91 on the gas pump means that the fuel from that pump has the same ability to resist detonation as a fuel blend made up of 91% octane and 9% heptane. The blend may not actually be 91% octane but the fuel behaves as if it were. Many things can be added to the fuel to increase the octane rating.

Back in the old days they used to put something in the fuel known as tetra ethyl lead (TEL) to increase the octane rating. This was back in the day when you had Regular, Unleaded, and Premium as your choices at the pump. The one called Regular is the one with the lead. Eventually we decided that it’s not a good idea to pump lead into the air so TEL was no longer used. After that we tried another compound called methyl tertiary butyl ether (MTBE) but this became controversial because it was found to be poisoning ground water.

The most common thing added to fuel today to increase the octane rating is ethanol. Fuel can be blended with up to 10% ethanol by law. Anymore ethanol than that and there is a risk of damaging fuel system components because ethanol is very corrosive. Many people oppose ethanol in the gasoline but at only 10% there are more benefits than detriments. Besides being an inexpensive octane booster, ethanol, being an alcohol molecule, has an oxygen atom in the mix. This makes ethanol an oxygenate, which provides extra oxygen at the point of combustion which in turn helps the air/fuel mixture to burn more cleanly.

Looking at the label on the pump that shows the octane rating this formula is always visible, (R+M)/2. Those with any level of mathleticism will easily see that this is a formula for a simple average of two numbers. R stands for RON, or research octane number, and M stands for MON, or motor octane number. These numbers are the results of the fuel being tested in two different ways. The research octane number is derived from calculations performed, based the blend of the fuel and how it should perform in theory. The motor octane number is derived from actually testing the fuel by using it to power a test engine. Ignition timing on the test engine is advanced until the engine begins the show detonation. The amount of advance that was applied will correspond with an octane rating that becomes the MON. The RON and MON get averaged out and you end up with the number on the pump.

The octane rating of the fuel is all about the ability of the fuel to resist combustion until the spark is introduced into the cylinder and nothing more. This number has nothing to do with the quality of the fuel. Nothing to do with the amount of power the fuel produces. Nothing to do with how clean the fuel is. Nothing to do with the amount of detergents in the fuel. Nothing to do with helping your engine or fuel system components last longer. In a round about way you might say that it could affect some of these things, but not directly, and not in most cars.

Cars that call for higher octane fuel are usually performance cars of some kind or another. These high output engines are built differently and tuned differently so they require fuel that will resist detonation. Things such as a higher compression ratio make for higher combustion chamber temperatures pre-spark. This higher temperature will light off a lower octane fuel. These engines also like to run with more timing advance which can cause the air/fuel mixture to burn too quickly leading to detonation.

If a lower octane fuel is used in an engine that requires a higher octane rating the least that will occur is less power output and lower efficiency (this is not because there is less power in lower octane fuel but because the engine will not run properly), and the worst that will occur is major engine damage. All new vehicles have the ability to limit detonation but only up to a point and only under some circumstances.

High octane fuel used in a car that doesn’t require it is simply a waste of money. No benefit can come from using a high octane fuel when it isn’t needed. Many people think it’s good because it costs more but this just isn’t true. Obviously high octane fuel doesn’t hurt the engine; it just hurts your wallet. The other condition that makes high octane fuel a waste is high elevation. At high elevation, anything over 4,000 ft. or so, atmospheric pressure is much lower than it is at sea level, and therefore oxygen density is also lower. Since atmospheric pressure is responsible for pushing air into a running engine, there will not be as much oxygen pushed in when the atmospheric pressure is lower such as it is at high elevations. This lower oxygen level, and lower pressure, in the combustion chamber automatically reduces the chance for detonation. This is why the lowest octane rating at stations in the mountain west, cities such as Denver or Salt Lake City, is 85 instead of 87 like it is at sea level.

If you live at sea level, go with the octane rating listed in your owner’s manual. If you live at a high elevation go with something lower. If you are not sure if it’s affecting the way your engine runs, try tracking you fuel economy, because any inefficiency in the way the engine runs will be manifested in the form of lower fuel economy. Don’t just put high octane fuel in your vehicle because it feels good to spend more. People could accuse you of working for the government.

Friday, August 19, 2011

The Rubber that Meets the Road

Saying that tires come in all shapes and sizes, isn’t exactly right. They do come in all sorts of sizes but the shapes are pretty much the same, round with a hole in the middle. They are all black and they all use air pressure to keep them working properly, although with all of the strange things that automotive designers have done over the years to change the style of the cars and trucks we drive, it’s kind of funny that they haven’t had cars with blue tires or red tires. The only thing they have ever tried is varying thicknesses of a white stripe around the sidewall.

Tires are an extremely important part of the car and yet they are always neglected or forgotten. Without decent tires a car turns into an instrument of death and chaos. That may sound silly but it’s pretty much true. The tires keep the car in control and sticking to the road at all times. When it’s going straight, and when it’s turning, when it’s on smooth clear pavement, and when it’s on rough, bumpy or slippery surfaces. The tires also contribute substantially to the ride quality. When considering that the tires are bouncy air cushions that the entire weight of the vehicle is resting on, it’s easy to see that a tire problem is going to affect the way the ride feels and the way the vehicle handles.

A very interesting tread pattern. Each row of tread is different
and grips differently from the rest.
Tires are meant to provide a way for the vehicle to stick to the road. The rubber compound that makes up the tire is what does the sticking. The depth of the tread doesn’t have much to do with causing the tire to grip. The tread on the tire is only there to move water and snow out from under the tire so that the rubber can meet the road. Some tread patterns are not meant for use in snow and ice and some are designed specifically for that purpose. If you drive your car in all types of whether then all-weather tires are what you want. They will give you adequate performance in all conditions, but they will not give you the best performance in any conditions.

Tire Sizes

The most confusing thing about tires is perhaps the way that tire sizes work. If you have ever looked at the sidewall of the tire you might have seen something such as P215/65R15 89H. Most of this seems like nonsense but numbers of course, mean things. Starting with the letter at the beginning, this is usually a P or an LT. P stands for “passenger” meaning the tire is intended for passenger cars. The LT stands for “light truck” and is intended for; you guessed it, light trucks. This is any truck or truck like SUV even if it’s a full size truck it is still only a light truck.

The number 215 is a direct measurement of the width of the tire in millimeters. This is pretty easy to understand but the next number 65, is the aspect ratio. This ratio is the measurement of the height of the sidewall of the tire expressed as a percentage of the width. So in this case the side wall height is 65% of the width of the tire.

The next letter R refers to the type of construction. In this case R stands for “Radial” meaning that it is a radial tire. A radial tire is a tire that has the steel cords inside laid out in a radial pattern. All common tires today are radial tires so it is really pretty rare to see something other than an R in this spot. Old tires might have a B for bias belted, or a D for diagonal bias.

The number after this letter refers to the diameter of the rim in inches. Why they size part of the tire in millimeters and part of the tire in inches makes no sense but that’s the way it is. Many old tire sizes were all in inches and some off-road tires can still be purchased this way. Something like 31X10.5 R15 would be an example of a tire size in inches. The total diameter of the tire is 31 inches, and the width is 10.5 inches, made to fit on a 15 inch rim.

The next number, in this case 89, refers to the load rating of the tire, or how much weight the tire can safely carry on a regular basis. The number is kind of an arbitrary value, the higher the number the more load the tire can carry.  These standards are set by the Department of Transportation and will normally range from 70 to 110.

The last letter which is an H on this tire, refers to the speed rating of the tire. A tire with a speed rating of H can safely be driven at speeds up to 130 mph without centrifugal force ripping the tire apart. The highest speed rating is Y which means the tire is safe up to 186 mph. Many people think that Z is the highest rating but the letter ratings skip around a bit. On very high speed tires a Z is added before the R so the tire will be called Z rated but this is not the case. The Z in this position indicates it is a tire that is intended for use over 149 mph but the actual speed rating is still at the end of the tire size number. A good example of this is 285/35ZR19 99Y. This is a Y rated tire not really a Z rated tire. Exceeding a tire’s speed rating is very dangerous and can lead to a high-speed blowout which may lead to a loss of control of the vehicle. Some light truck tires might have a P or Q rating which is somewhere between 90 and 100 mph. The vehicle these tires are mounted on may easily go faster than this. Driving a vehicle with one of these tires faster 90 to 100 mph would not be a good idea.

One more marking worth a mention, all-weather tires will either say all-weather or all-season on the side, or they will be marked with M+S which stands for mud and snow. Unless you live in a place like Phoenix, Arizona or your vehicle is only used under certain weather conditions, all-weather tires are probably the best option.

Tire Maintenance

Of all of the important systems on a car that require maintenance, tires are probably the easiest and the cheapest to maintain. All that really needs to be done is regular pressure checks and an occasional tire rotation. Despite the fact that this stuff is cheap and easy, most people do not have these things routinely performed on the cars that they drive. That’s their choice but remember the instrument of death and chaos? That is what results from a lack of maintenance.

Every vehicle on the road should have a tire pressure gauge in the glove box so that tire pressure can be checked a couple of times a month. Most gas stations have an air hose that can be used to inflate the tires if needed, and probably 25% of those air hoses are actually in proper working order so you should be able to find a place where you can check your own tire pressure, and top them off if needed. Checking tire pressure with a run of the mill tire pressure gauge requires no skill, and neither does filling the tire with air. Most automotive technicians will gladly charge you to check your tire air pressure for you, and maybe they will even do it for free, but guaranteed they will mock your laziness or ineptitude behind your back because you cannot check them yourself.
Wear indicator between the tread blocks touching the
pavement. This means that the tires are worn out.

In order to find out what your tire pressure should be you can look in the owner’s manual, but if this is lost, or just too confusing, the other place that you can look is on the tire information label. This label is usually posted somewhere on the inside edge of the driver’s door or driver’s door frame. If the label is not there it could also be on the inside of the glove box on under the lid of the center console. Do not look on the side of the tire. This will only tell you the maximum pressure that the tire can stand before it becomes dangerous once it gets hot.

Tire rotation is something that you could easily do yourself with a few simple tools but since the car must be lifted you may just want to have this done by a professional. Tires should usually be rotated about twice a year. This usually works out to be about every 6,000 to 7,000 miles. Some special off-road tires or snow tires with very soft tread may need to be rotated more often.

The reason tire rotation is important is that it allows the tires to wear more evenly. The front tires on a vehicle with front wheel drive will wear out the front tires much faster than the rear tires because the front tire both steer and propel the vehicle. Vehicles with rear wheel drive usually wear the rear tires a bit faster than the front. If the wheel alignment of the vehicle is not perfect the tires will wear even more unevenly. Sometimes the tires on a particular vehicle just won’t wear well even if the alignment is good. Proper rotation will always make the tires last longer.

Tire Problems

Uneven wear is the most common tire problem. When the tread doesn’t wear the same across the entire tread surface on the same tire, it is called uneven wear. Things that usually cause this are wheel alignment problems or tire inflation problems. Wheel alignment problems can be caused by a lack of proper adjustment, or worn out or damaged parts. This must be diagnosed by someone who knows what they are doing. If the tires are worn more heavily on one edge of the tire compared to the opposite edge then there is an alignment problem. If the wear in the tire appears wavy or if individual tread blocks seem to be wearing on an angle then this is probably an alignment problem.
This tire has good tread over most of the surface, but the
right side is so work out the steel cords are poking through.
This is a major alignment problem.

Tire inflation problems that cause uneven wear can be easily diagnosed by anyone. If the center of the tread around the circumference of the tire is worn more than the outside edges of the tread then the tires have likely been run while overinflated. This is common because many people don’t use a pressure gauge when they put air in their tires. They put air in and just look at the bulge in the sidewall where it sits on the ground to come up with a guess as to when to stop pumping the tire full of air.

If you see the opposite condition, wear on the outside edges but not down the center, then the tire has been underinflated. This is common because it means that the tire pressure is never checked and the car is driven without enough air in the tires. If either one of these inflation conditions is caught before the difference in wear is extreme then the pressure can be corrected and monitored and the tires will usually even themselves out.

The tire on the left is underinflated. The tire in the middle is overinflated.
The tire on the right is normal.
 Other problems or forms of tire wear are an indication of a defect in the tire, or the inner carcass of the tire coming apart. If the tread of the tire seems to be worn around just a portion of the circumference, but the rest of the tread along that same line around the tire looks better, then the tire is experiencing tread separation. This means that the tread layer of the tire is detaching itself from the carcass. Another condition that may be noticed with tread separation is a vibration that begins around 30 to 35 mph but then disappears around 50 mph. Sometimes this is mistaken for an imbalance but it is not. An imbalance in the tire and wheel assembly will cause a vibration that will usually begin at a higher speed but will only get worse as speed increases, and will never just vanish. Tread separation is very dangerous and the tire must be replaced to correct this condition.

Major tread seperation. Notice the big deep crack on the right side.
This is a very damgerous tire, not to mention that the ride quailty of this
vehicle was terrible.
A true tire blowout of the worst kind.
A bulge in the sidewall is also a dangerous yet common condition. This means that the steel cords in the sidewall have broken allowing the air pressure in the tire to cause the bulge in the rubber. This is a weak spot that will be prone to complete failure at some point, but will most likely fail at high speed when the tires are their hottest and the pressure is the highest. Many times the broken cords are the result of the vehicle taking a curb shot. If the car is driven into the curb or slides into the curb in the winter, the sidewall gets pinched and it can break the steel cords. A tire with a bulge in the sidewall must also be replaced and cannot be repaired.

A Doughnut You Can’t Eat

If the tires are very neglected, the spare tire is even more so. The main thing to remember with the spare tire is to check the pressure once in awhile. Many times people find a flat tire on their vehicle and go to put the spare on only to find that it too is flat or at least very low. The other thing is that spare tires are usually meant for temporary use and should not be used for extended periods.

If you are lucky, the spare tire on your vehicle is a regular full size tire and not one of the temporary doughnut spares. These compact spares are now the standard on most cars because they are cheap, they are light, and they are easy to stow. Anything that manufacturers can do to make a car cheaper, lighter, or easier to package, will be done, even if it comes as a compromise. The problem with these little spares is that they are not meant for speeds much above 55 mph. They are only meant to get you to a tire shop in the next town. The problem is that this is not very convenient because stopping at a tire shop in the next town isn’t always convenient.

Some four-wheel-drive vehicles and SUV’s will have a doughnut that is full-size. These don’t have quite the same restrictions as the small ones but they are not the same thing as having a regular full-size tire for your spare. If you do have a regular tire and if the rim matches the rest of the rims on the vehicle, you can rotate your spare through the regular rotation. This will allow you to actually use that tire and it will make all of the tires last a bit longer.

You Get What You Pay For

When buying new tires it goes without saying that you should buy tires that are the same size as the ones that the vehicle came with. Changing the size of the tire will change the way the vehicle rides, handles, and it will also cause your speedometer and odometer to read inaccurately. Sometimes some custom rims can add a nice look to your ride and this is okay to do as long as the overall diameter of the tire remains the same. So if you vehicle came with 16 inch rims and you want to put 18 inch rims on it,  change the tire to something with a smaller aspect ratio. The new aspect ratio must be 1 inch shorter which will add two inches to the inside opening of the tire.

The other thing to remember when buying tires is that you get what you pay for. Don’t buy cheap tires, it’s not worth it. This doesn’t mean that the most expensive tires are the best tires; it just means that you should always try to spend a little extra. The problem with the cheap tires is not just that they tread wears out quickly, but they usually suffer from other problems before the tread wears out. Things like vibration problems, tread separation, conicity issues (a condition that can cause the vehicle to exhibit problem with wheel alignment when really there are none), and other things render the tires useless while there is still tread left.

Stay Connected

To the road that is. There are a few systems on your vehicle where you never want to see failure while driving, and the tires are one of them.  If your engines blows up while driving down the road, no big deal. If your transmission falls out on the freeway, it doesn’t matter. If one of your tires gives up at 80 mph, or if you have no tread left and you hit a big puddle at high speed, then watch out because you may not be able to keep it under control. Take care of your tires; remember that your life is riding on it.

Monday, August 15, 2011

OBD I and OBD II Are Not Star Wars Characters

Can you just hook a computer up to it?

Back in the late 70’s and early 80’s, someone thought it would be a good idea to start putting computers on cars to control all of the various vehicle systems. This started out very gradually at first with just the control of engine operation being handed over to a mysterious little box with a bunch of wires hanging out. Cars today not only have multiple computers but all of the computers are link together on a network.

Computer controls have been very good for the automobile because they have made all of the various systems much more efficient, and they have allowed many more important features to be added to the average car. Some people complain that all of the complex computer control systems aren’t necessary and that the old systems are better because they are simpler. Well if simplicity is the primary goal then the old systems are better. Considering that computer controls help vehicles have more power and get better gas mileage, it may be worth it to sacrifice simplicity.
A typical engine control computer. Notice the two big connectors with hundreds of wires.
Despite that fact that computer controls do add a certain level of complexity, there is another thing that is possible when something like engine operation is controlled by a computer. That thing is called on-board diagnostics (OBD). If the computer has the capability of receiving inputs, processing those inputs, and then controlling outputs, it can easily have the capability of verifying each one of its functions, and the functions of the things that it controls.

Early systems were not very smart and therefore had very little in terms of OBD. The first fuel injection systems had no OBD, but as these systems have gotten more complex, they have also been able to do more and more to monitor themselves, and make this monitoring information available to technicians.

The first thing that was available from OBD systems was the diagnostic trouble code (DTC). When the computer finds a problem somewhere in its systems it will set a DTC in its memory and turn on a malfunction indicator lamp in the instrument cluster. This is the “check engine light” that everyone is familiar with when a problem is found in the powertrain controls. If the problem is with the Anti-lock braking system then the ABS light comes on, and so on with all of the computer controlled systems. The driver of the vehicle will see that there is a problem and they will take the car in for repairs. Or they might just put a piece of black tape over the light so it won’t bother them while they are driving.

The technician will have to extract the trouble code from the vehicle’s computer to see where or what the problem might be. Sometimes this will mean that a special computerized tool will be hooked up to the car and the code will be extracted via the data link connector (DLC). Most of the early vehicles with OBD also provided a way to read the codes without the scan tool. This usually meant that a couple of terminals in the datalink connector could be jumpered with a wire, or some similar procedure could be performed to read the codes. In this instance the MIL will flash in sequence revealing what the DTC is. Every manufacturer had a different procedure for reading these “flash codes,” and the DLC design and location was always unique as well.

The next thing that OBD made available to help diagnose a failure in a computer controlled system was serial data. This is the data that reflects the inputs to the computer, and control of outputs by the computer. So most info going into the computer, being processed in the computer, or being controlled by the computer, can be seen in the serial data stream. This data must be accessed with a scan tool and cannot be accessed any other way. Some high-end cars provided a way for the technician to access all kinds of information, including DTCs, and serial data, via the climate control system display, or some other control system on the dash. This is pretty rare, but every car has data available via the scan tool.

Serial data can be used to see if the computer is getting a false reading from something like the coolant temperature sensor, or the mass airflow sensor. The serial data will also show what the computer is doing to control the air/fuel ratio. Fuel injector on time can be observed along with weather or not the exhaust gases indicate a lean or a rich condition. With a fair amount of practice this data can be easily interpreted by the technician to help them pinpoint a problem.

Because of differences in communication protocols, every auto manufacturer required a different scan tool back in the day, in order to see serial data as well as read trouble codes. The location and shape of the DLC was also different from one car to another. This meant that if you had a Ford and the shop you took your car to when the MIL illuminated, didn’t have a scan tool that could talk to Fords, they might not be able to work on your car. Every manufacturer also used there own trouble codes so that a code 15 on a Dodge meant something totally different then a code 15 on a Honda. Along with different numbers, some of the terminology used to describe trouble codes and bits of hardware were completely proprietary adding more confusion to the diagnostic process.

Not long after computer controls hit the market, a solution was reached that could help most auto shops take advantage of the OBD of most cars. Aftermarket tool companies developed scan tools that could communicate with most if not all, of the major auto manufacturer’s products. These new scan tools came with a connector for almost every DLC, and the ability to communicate with most vehicle control computers. These generic scan tools worked very well for the most common cars but some of the more obscure makes were impossible for technicians to work on unless they worked at the dealership where the car was sold, and had access to tools and information from that specific manufacturer.

The primary failures that cause the check engine light to illuminate are failures that cause emissions levels from the vehicle to increase beyond a certain level. With the difficulty that technicians had in not being able to diagnose any car that came into the shop the result was some cars were left unrepaired which meant that they were putting more pollution into the air. Because of this the U.S. Congress and the Environmental Protection Agency decided to get involved. Through modifications to the Clean Air Act, new standards were developed that would mandate some standardization in the OBD systems used by every manufacturer selling cars in the U.S.
A basic OBDII scan tool.

This new standard is known as OBDII. The first year that this new system was mandatory was the 1996 model year. All cars have to have the same DLC, and they all have to put the DLC under the dash on the driver’s side. Every car company has to use a similar communication protocol so that a generic scan tool can be used to read DLC’s from any vehicle on the road. So now if you have an OBDII scan tool you can read codes on a Buick just as easily as you can read codes on a Rolls Royce.

Under OBDII each vehicle also has to have the ability to run the same monitors on the same systems for each make and model. These monitors will be run by the computer when certain enable criteria are met. These criteria are operational conditions that occur during normal vehicle operation. A system monitor will run in a way that the driver will not be able to detect, and some monitors are running continuously anytime the vehicle is in operation. Some of these monitors are so smart and so sensitive that they can even tell if your gas cap was left loose or missing altogether. The computer looks for this condition because a loose gas cap releases pure unburned hydrocarbons directly into the atmosphere to react with sunlight and create smog. The serial data that can be read with the scan tool also has to be very similar when being read with a generic scan tool in the OBDII mode.
The OBDII DLC under the dash on the driver's side. This
is where the scan tool gets plugged in.
All of the basic trouble codes are also standardized using an alphanumeric structure. The code P0302 is an example of a common OBDII code. The letter and every number mean something and the meaning is the same on every car. Some codes can still be specific to the manufacturer but the structure of the code must follow the same guidelines which allow the technician to quickly tell if it is a generic code or a manufacturer specific code. All basic terminology used to describe systems and parts of systems related to parts, codes, and failures also follow specific OBDII guidelines.

A very fancy and expensive manufacturer
specific scan tool.
Since 1996 OBDII has evolved somewhat to further standardize various features of the onboard diagnostic system. All of these things have made it easier for technicians to diagnose any car, and for aftermarket equipment manufacturers to build useful and effective tools to aid in the diagnostic process. While a good generic scan tool can communicate with any car on the road built since 96, the manufacturer specific scan tools are still the best, and still provide the most functionality.

Despite the fact that computer controlled cars have the amazing capability to check themselves out, this does not mean that the technician needs to only hook up to the car’s computer in order to see everything that is wrong. Some people will take their car into the shop when the check engine light is on and get annoyed or angry when they are told that they have to pay 75 to 100 bucks just to find out what is wrong. The technician must use their expertise along with their expensive computer diagnostic equipment to diagnose a very complicated system. Why should they have to do this for free?