Chart A-2 Code 12 Will Not Flash

Fig. 050 - Wiring Diagram for Chart A-2 Code 12 Will Not Flash. VIN O, VIN 2, VIN R, VIN U,:

CHART A-2

WON'T FLASH CODE 12

("SERVICE ENGINE SOON" LIGHT ON STEADY)

1.8L "J" AND 2.5L " A & N SERIES

FUEL INJECTION (TBI)

There should always be a steady "SERVICE ENGINE SOON" Light when the ignition is "on" and engine stopped. Battery ignition voltage is supplied directly to the light bulb. The Electronic Control Module (ECM) will turn the light on by grounding circuit 419 to the ECM.
With the diagnostic terminal grounded, the light should flash a Code 12, followed by any trouble code(s) stored in memory.
A steady light suggests a short to ground in the light control circuit 419, or an open in diagnostic circuit 451. A steady, but dim light would indicate failed Quad-driver. The Chart will confirm and suggest the cause.

Fig. 047 Chart A-2 - Code 12 Will Not Flash:

1. If the light goes off when the ECM connector is disconnected , then circuit 419 is not shorted to ground. Take this opportunity to physically check the connector terminals for proper contact.
2. This step will check for an open diagnostic circuit 451.
3. At this point the "SERVICE ENGINE SOON" light wiring is okay. The problem is a faulty ECM or PROM. The ECM is OK if a Code 51 is stored when the PROM is remove. Replace the PROM.
4. Solenoids and relays are turned "ON" or "OFF" by the ECM using internal electronic switches called "drivers". Each drivers is part of a group of four, called "Quad Drivers". Failure of one 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".

Before replacing ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM. See ECM wiring diagram for the solenoids and relays and the coil terminal identification.

When checking TCC solenoid, be sure to raise drive wheels and run above 30 MPH to close third gear apply switch.