Sensor and Car Computer Problems

General Motors engine control moduleGM Engine Control Module

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. This 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 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.

How Often do Car Computers Go Bad

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.

GM ECM (Electronic Control Module)Next Generation GM ECM

I quickly learned 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.

Do Car Computers Ever Go Bad

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.

How to Diagnose Car Computer Problems

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 is usually the output of a reference voltage problem. When this happens a car might possibly set a throttle 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 issue that appears to be car computer problems.

ECM Power RelayECM Power Relay

In some isolated cases we've seen coolant temperature sensors allow antifreeze to travel the length of the reference signal wire and wet the connector of the ECM.

This 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 will set power codes like a P2509, power input signal fault. The ground connection is just as important as the power. Corrosion can cause ground integrity issues. Find the system grounds and make sure they are clean and tight.

How to Replace Computers on Old Cars

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.

Fix Car Computer Problems and Sensor Issues

This is a popular area of the website. Give this page a bookmark and check for new content related to common car sensor issues and computer problems.

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