ECM FAILURES/SHORTED SOLENOIDS TCC SOLENOID MALFUNCTION

ECM failures on EFI equipped vehicles could be due to any shorted relay or solenoid that is controlled by the ECM, although, the most likely is the TCC solenoid.

This condition may exist if the "Check Engine" light originally goes "on" and stays "on" while the torque converter clutch would normally be applied, and diagnosis indicates a faulty ECM. When the diagnostic "test" terminal is grounded the light may try to flash a Code 12, from "bright" to "dim" instead of "on" and "off."

If a shorted relay or solenoid is suspected then check the resistance and replace it if it measures under 20 ohms. In order to check the resistance of an installed TCC solenoid, the drive wheels must be turning fast enough to close the third gear switch inside the transmission. If the relays and solenoids check ok and the "Check Engine" light still only goes on when the TCC applies, then check the TCC solenoid at operating temperatures since the diode connected across the TCC solenoid may only malfunction after it has reached higher temperatures.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.