Where Is the ECM in a Honda Civic?

Written by bridgette ashmore
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Where Is the ECM in a Honda Civic?
Cars are equipped with computers. (Honda S2000 AP1 - 2002 s/w image by Christian Schwendemann from Fotolia.com)

The Engine Control Module (ECM) or Engine Control Unit (ECU) monitors your engine's performance and provides data about many aspects of your car. Like the other parts of your Honda Civic, the ECM should be checked periodically and may require changing from time to time. A bad ECM can produce faulty readings and missed diagnostics.

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Locating the ECM

You will find the ECM in most Hondas, including the Civic, on the passenger side. In order to access it, you must lift up the carpet on the passenger side floor. If the carpet is difficult to pull back, you may also need to loosen the kick plate. Underneath the carpet is a large, heavy protection plate secured to the floor with 10-millimeter screws. Remove the screws and take off the protection plate. There are additional plugs that also have to be removed; these can be extracted by pressing in the centre of the tab and pulling it away from the unit.

Identifying the ECM

Once you have removed the protection plate, you will see several parts in this area. The transmission computer can be identified by the prefix of its part number, which should be visible. If it starts with 28100, it is the transmission computer. The ECM will have the prefix 37820.

Looking for Damage

Once you have located and removed the ECM, you can open the case by removing the four screws around the perimeter. Take care not to strip the screws. By opening the case you can look for obvious signs of damage such as burn marks or corrosion. This can help verify your diagnosis. Remember though, if you don't see anything, it does not mean there are no problems. A visual inspection is merely meant to aid the diagnostic process; it is not definitive.

Diagnosing a Problem

When the transmission computer is malfunctioning, it puts the car into "safe mode," which is third gear and reverse only. In addition the D, D4, S or Sport light (depending on your specific model) may flash or simply stay on. When the ECM fails, the car may still run, but it will collect incorrect error codes. These codes could cause incorrect driver displays, such as the malfunction indicator light. If you suspect a faulty ECM, you should not ignore it, even if your car is running. The ECM controls the ignition system, the fuel and the emission controls, and serious damage can accrue over time if not addressed. Some problems will shut your car down and prevent it from running.

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