For 1990-2009 cars

# 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 CAME "ON" WHILE THE TORQUE CONVERTER CLUTCH WOULD NORMALLY HAVE BEEN APPLIED THE LIGHT WOULD THEN STAY ON, AND DIAGNOSIS INDICATES A FAULTY ECM. WHEN THE DIAGNOSTIC "TEST" TERMINAL IS GROUNDED, THE LIGHT MAY FLASH A CODE 12, "BRIGHT" TO "DIM" INSTEAD OF "ON" AND "OFF". IF A SHORTED RELAY OR SOLENOID IS SUSPECTED THEN CHECK THEIR RESISTANCE AND REPLACE IF IT MEASURES UNDER 20 OHMS. TO CHECK THE TCC SOLENOID, THE DRIVE WHEELS MUST BE RAISED FROM THE FLOOR AND DRIVEN FAST ENOUGH TO CLOSE THE TRANSMISSION 3RD GEAR SWITCH. IF THE RELAYS AND SOLENOID CHECK OK AND THE "CHECK" ENGINE" LIGHT ONLY GOES ON WHEN THE TCC APPLIES, THEN CHECK THE TCC SOLENOID AT OPERATING TEMPERATURES SINCE A DIODE CONNECTED ACROSS THE TCC SOLENOID MAY ONLY MALFUNCTION AFTER IT HAS REACHED A HIGH TEMPERATURE.

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.