Chart A-1 No Service Engine Soon Light

There should always be a steady "CHECK ENGINE" light when the ignition is "on" and the engine is stopped. Battery is supplied directly to the light bulb. The Electronic Control Module (ECM) will control the light and turn it on by providing a ground path through circuit 419 to the ECM.

1. No "CHECK ENGINE" light suggest a faulty light bulb or open control circuit 419. Be sure test light is connected to 12 volts when making check (1.)
If test light will not light there may be battery supply problem to the ECM. This would normally be an "Engine cranks but won't run" symptom.
2. and 3. These steps check for ignition and continuous battery voltages.
4. Solenoids and relays are turned "ON" or "OFF" by the ECM, using internal electronic switches called "drivers". Each driver is part of a group of four, called "Quad-Drivers". Failure of ECM driver can damage any other driver in the set. Solenoid and relay coil resistance must measure more than 20 ohms Less resistance will cause early Failure of the ECM "driver". Using an ohmmeter, check the coil resistance of the following solenoids before replacing the ECM.
^ TCC Solenoid.
^ A/C Relay -opposite harness connector terminals "A" and "C".
^ Fan Control - opposite harness connector terminals "B"and "C".
^ Wastegate Solenoid.