This car computer problems page will connect you to in-depth and detailed articles about common automotive sensor problems.
You can scroll to the bottom and rummage through the list of topics. Better yet, you can read your way down there and learn about the heart of the engine management system.
The computer, also called an engine control module, receives inputs from the individual sensors. The plastic throttle position sensor provides an excellent example of an input sensor. All data is analyzed in the same module. Using this received information the ECM Outputs commands to the various control devices like the fuel injector and the ignition control module.
Here we’re going to talk about the difference between computers mounted in automobiles from the 80s and 90s and the vastly different units found in vehicles from the late 90s and 2000 decade. More importantly, we'll talk about properly diagnosing car computer problems and how to replace them when needed.
This is a complicated question that has a lot to do with the year, make and model car it's installed in. Nevertheless, I’ll say the general answer of not often, but provide a further explanation.
In the mid-80s when these computers started showing up in every car built so it could comply with stricter emission standards and fuel economy ratings, mechanics wanted to replace them often.
The lack of proper training led to many misdiagnosed and wrongfully replaced modules. Often the root cause of the driver complaint turned out to be a tuneup or maintenance problem. As a young dealership line technician from this time period my employer sent me to intensive factory training.
I quickly learned to use automotive diagnostic code readers and figured out how to tell the difference between a bad computer and one that was malfunctioning for various reasons.
I will share details with you, but I wanted to make you understand how General Motors felt about how often the car computer fails. After studying the returned units, less than 10 percent actually had a malfunction.
This meant that 90 percent of the replaced ECM's had nothing wrong with them. Another conclusion from the study found that dealership technicians replaced multiple sensors and computers for a single driver complaint.
At that point General Motors adopted a policy of replacing only one part per driver complaint. Dealerships submitting multiple parts on a single line ticket would have that claim bounced. In other words, you could no longer throw a Chevrolet 02 sensor part on a claim with a failed powertrain control module.
The short answer is yes, they do fail at times. In fact General Motors had a blunder with one of their most popular control modules. After 30 years of water under the bridge I still remember the ECM part No. 1227730.
This particular unit became plagued with problems. The main circuit board was thin and brittle. They went into millions of cars from the model year 1987 through 1993.
Some really popular cars like the Cavalier, Firebird and Camaro had this computer. These vehicles also had a new design mass airflow sensor. The sensors worked so poorly that General Motors had to come out with a special repair policy.
The fix was to replace the PROM (Programmable Read Only Memory) unit on the ECM board with a reprogrammed set of instructions. General Motors called this the speed density update.
Basically it used the manifold absolute pressure sensor for engine load data instead of the mass airflow sensor. When mechanics replaced the PROM they had to seat it on the weak motherboard. The operation would cause hairline cracks and intermittent operation of the ECM.
These cars would come back multiple times for intermittent car computer problems that were difficult to search down. Eventually the General figured out that any unit with a 1227730 ECM that had the speed density update performed, would probably need a replacement computer.
In many cases it's not the controller or the module, but the sensors they read and the actuators they control that remain the root cause. As an example, the Honda VTec solenoid and spool valve fail more often then the module that energizes them.
In the example of the 1227730 ECM, mechanics came up with an easy trick to diagnose a bad unit. If the circuit board had hairline cracks you could tap the outer case of the computer with the handle of a screwdriver.
If it needed replacing the check engine light came on and the engine ran poorly. On newer automobiles it's much more difficult. When I say newer, I'm talking about old cars from the 1990s and early 2000 model years.
When these vehicles have a bad ECM it's usually the output of a reference voltage problem. When this happens a car might possibly set a crankshaft position sensor code, because a 5 V reference wasn't sent out from that ECM. This kind of pinpoint diagnosis takes some skill and a good auto repair manual.
Another way to check for a computer failure is to disconnect the bulk connectors. You can inspect the terminals for corrosion and looseness on both the ECM and connector sides. Even a small amount of corrosion can cause an issues.
In some isolated cases we've seen defective coolant temperature sensors allow antifreeze to travel the length of the reference signal wire and wet the connector of the ECM.
This small amount of moisture can easily destroy an engine control module. Long story short, when you unplug a control module it should look like brand new inside. Finally, every computer needs power and a good ground.
Many models use a computer power relay. These can fail and the ECM sets power interruption codes like a P2509, power input signal fault. Of course, the ground connection becomes just as important as the power. Corrosion can cause ground integrity problems. Find the system grounds and make sure they are clean and tight.
On vehicles from the 1980s and early 90s, they stored the model specific fuel management operation instructions on a self-contained replaceable part called the PROM.
This meant when a computer failed you physically switched the PROM chip over to the new unit. The simple procedure didn’t require the need for any special equipment. When vehicles went to OBDII in 1996 they changed to a prom soldered to the circuit board.
Now a replacement ECM requires the use of a flash memory device to program the new computer. Replacing a car computer at home isn't really possible like in the old days. However, this doesn’t mean you have to buy an expensive replacement unit at the dealership.
Aftermarket companies offer refurbished and new replacement car computers. The prices vary with year, make and model, but are usually discounted from retail in the 50 percent range.
Unfortunately, you’ll to have to take the car to a dealership and see if they’re willing to install this aftermarket unit and then flash the prom with your vehicle's instructions.
If everything works out, using this procedure might save several hundred dollars. The dealership will at least charge one hour labor at their going rate to flash the new computer.
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Speaking of emission system vapor codes, If you have a GM car or truck from the 2000 decade you might have a fuel tank pressure sensor issue at some point. See how to test and replace the part.
A no start condition on an old Ford is a common problem. This article walks you through diagnosis of the ignition side of the circuit and shows you how to test the Ford ignition module.
The cars computer needs to know the incoming air temperature to calculate the fuel mixture. Here's what happens when the intake air temperature sensor goes bad.
Even reliable Japanese cars have check engine light issues. See the massive amount of cars setting Nissan knock sensor codes.
Another interesting article related to General Motors products. Three separate generations of GM ignition control modules suffer from a high failure rate.