How do you test for a bad ECM?

Testing for a bad electronic control module (ECM), sometimes called an electronic control unit, requires the use of computer diagnostic equipment. However, there are clues drivers can watch out for to determine if their ECM may be going bad.

ECM problems often manifest themselves in common ways. To determine if a vehicle has a bad ECM, look for some common signs and symptoms.

1. The car will not start

If an otherwise well-maintained car will not start, rule out things like the battery, starter and other electrical problems. If the problem persists, have the ECM checked out.

2. The check engine light

Look out for the check engine light that comes on and does not turn off. The most common reason for the check engine light to come on is a faulty ECM.

3. Other common symptoms

Look for other symptoms that suggest the ECM might be failing, such as a dramatic unexplained drop in fuel economy, or a lack of engine performance.

An automotive technician will hook the car up to a diagnostic computer and the diagnosis will cost anywhere from $150 to around $300. If the vehicle needs a new ECM, plan on spending anywhere from $1,000 to $3,000 to have it replaced. In some cases, the mechanic may be able to reprogram the ECM, saving the driver a considerable amount of money.