Chart A-2, No Code 12 "Check Engine" Light On Steady

Steady "CHECK ENGINE" light should be on with ignition "ON" and engine not running. Battery voltage is supplied directly to the bulb. With the diagnostic terminal grounded the light should flash a Code 12 followed by any other trouble codes stored in memory. A steady light indicates a short to ground in the light control circuit 419, or an open in circuit 451.

1. If the light goes off when the ECM connector is disconnected, then circuit 419 is not grounded. Also check the connector terminals for proper contact at this time.
2. This step checks for an open diagnostic circuit 451.
3. This step checks for a faulty ECM or PROM. If Code 51 is stored when PROM is removed, replace PROM.
4. Solenoids are turned on and off by the ECM, using internal electronic switches called "Drivers". Each driver is part of a group of 4, called "Quad-Drivers". Failure of 1 driver can damage any other driver in the set.

Fig 1: Chart A-2, No Code 12 ("CHECK ENGINE" Light On Steady)

Fig 2: Chart A-2 Schematic