The term ECU stands for Engine Control Unit or Electronic Control Unit. Your vehicle may have more than one electronic module and the ECU, in this case, controls the engine performance. You may also find this part listed as a PCM or Powertrain Control module. In addition to controlling operations, these modules can communicate failures to off-vehicle diagnostic equipment.

A standard engine module controls the timing, idle speed and air to fuel mixture. For timing control, the module adjusts the spark for the best balance of economy and power. It will increase the amount of fuel in a mixture until the engine warms up and controls the idle RPM. Vehicles with Variable Valve Timing also use the ECU to control valve opening. Valves should open earlier at higher speeds.

User programmable modules are also available. Some adjustable areas include how much fuel is sent to individual cylinders; spark firing for individual cylinders and maximum RPM.

ECU Failures

These control modules contain microprocessors and, like any computer part, failures do occur. One of the largest causes of failure is when excessive current passes through the device. If your vehicle was jump-started and the polarity was reversed, your module could be damaged. If the check engine light remains on after a reset, the module may be at fault. Because these units control a large portion of the engine operation, poor performance could indicate failure. However, you must thoroughly check all of the individual components before assuming the ECU has failed.

A bad spark plug, contaminated gas and many other common problems should be checked first. Most automotive parts stores have the diagnostic equipment available to read diagnostic trouble codes. Many ECUs can also be tested individually. You should also take the time to determine why the part failed to prevent the problem from reoccurring.

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