Computers, computers, computers! They are complicated, expensive, very unreliable, and mostly unnecessary. This is why I drive a 1988 Grand Caravan. It only has an engine computer. Everything else has been very trouble-free, and the systems are simple to diagnose.
Your car has an engine computer which is the one they're referring to. You also have separate computers for the Air Bag, Transmission, Body, Anti-lock brakes, Instrument Cluster, and Remote Keyless Entry. The Body computer, for example, is what locks your doors automatically at 15 mph. After all, you are too stupid to push a button when YOU want the doors to lock. How did we ever drive cars years ago without all these computers?
I'm sorry I'm not a driveability expert, but I can tell you there is a specific set of conditions that must be met to initiate a self-test procedure within the engine computer. Chrysler calls this a "Global Good Trip". They should have described the conditions to you at the dealership or the testing center. In many places, no further testing is required if the self tests pass. You may need to hold a steady speed on the highway for a certain number of minutes. The engine must be up to normal operating temperature. You might need to coast for a specific period of time, etc.
Usually a failure to pass the self test is not a fault of the computer; it's the fault of something the computer is monitoring, or the tests haven't been run because the enabling conditions haven't been met. One such condition is there must be no diagnostic fault codes in the engine computer's memory. Not all codes turn on the "Check Engine" light.
Be very careful if you try a salvage yard computer. The right computer will run your engine but there are often software upgrades that are done at the dealership. The used computer might have older software. Much more importantly though, if your car does not have the factory anti-theft system, you must NOT use a Body or an Engine computer from a car that had anti-theft. There's three possible scenarios.
First, if neither car has anti-theft, you can swap computers with no problem.
Second, if your car has anti-theft, you can use a computer from a car without it, but you can't put the computers back, so don't use a computer from your friend's car thinking you'll give it back later. The anti-theft programming in your car's Body computer will teach the new engine computer that anti-theft is on the car. Once that self-programming is upgraded to anti-theft status, it can not be undone. If you put the borrowed engine computer back into the original car that does not have anti-theft, it will teach it to the Body computer which will self-program itself. That too can not be undone. Both computers will be watching for the disarm signal when you try to start the car. It's never coming. Now you have to replace BOTH the engine and body computers. If you just replace one first, then the other, they will just keep teaching the anti-theft upgrade to each other.
Third, if the engine computer from the other car has anti-theft, it will not work in your car because it doesn't have that system to provide the disarm signal that allows the engine to start. It will also self-program the body computer into requiring the disarm signal that is never coming. Now you have to replace both computers in your car before it will start.
What this all boils down to is you MUST ask for an engine computer that came from a car without the factory anti-theft system if your car doesn't have that feature. If you do have anti-theft, you can use any computer, but from then on, that computer will only work in cars with the anti-theft system.
The part number printed on the label only assures you it's the correct computer for your engine, year, and model. You can not tell if it has been "upgraded" to the anti-theft system. If your car does not have anti-theft, you have a 50 / 50 chance of getting a used computer that works fine vs. You will need to replace both the Body and Engine computers. At $300.00 to $500.00 each, you can see why I drive an old car.
Be lucky you don't have a GM product. They can have up to 47 computers! Fords and the newer Chrysler are just as bad. Plus, with the GMs, pressing one button on the hand-held GM diagnostic computer electronically locks all other 46 computers to the Body computer which is built into the radio. (That forces you to have the factory radio repaired at grossly over-inflated prices - GOT'CHA!). Once "locked", you will never know anything was done, ... Until you need to replace the Body computer. Since all the other computers are locked to the Body computer, they must ALL be replaced too! Can you imagine the cost of 47 computers and the time and labor charge to install the software into each one? GOT'CHA! People are getting wise after being stung by these repair bills and are refusing, like me, to buy new cars. Funny thing is, the big wigs can't figure out why.
If no one else replies with the conditions you must meet on the drive cycle, ask at the dealership or testing center. Even if they did replace the engine computer, you're still going to have to drive it before it will pass the self-tests.
Tuesday, April 7th, 2009 AT 12:44 AM