Manual Transmission

Chart A-2 - ECM:

Diagnostic Circuit:

CIRCUIT DESCRIPTION
The ECM check is made to determine why the MIL remains "ON" or does not flash DTC 12. Normally, the ECM will not recognize a fault for at least 10 seconds after start-up. If the MIL remains "ON", the ECM has lost power, ground, or the signal that turns MIL "OFF" has been lost.
When the engine is started, the ECM grounds terminal "A10" to turn "OFF" the "Service Engine Soon" light. When ALDL terminal "B" is grounded it alternately grounds and opens "A10" to flash a code.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step checks for short to battery voltage in wire terminal "C" or faulty lamp driver.
^ Normal voltage reading is 9 - 11 volts.

2. This step checks to see if problem is related to the ECM or lamp driver. Normally, grounding terminal "C" should turn lamp "OFF".
^ If it does, the problem is related to the ECM and its wiring.
^ If not, it is related to the lamp driver and its wiring.

3. Grounding terminal "A10" at ECM and finding light "ON", indicates an open in CKT 487 to terminal "C" of lamp driver. Normally, grounding terminal "A10" should turn lamp "OFF".

4. This step checks for open CKT 451 from ECM to diagnostic terminal in DLC connector. The lamp should flash DTC 12, when terminal "A6" is grounded.

5. Checks for proper voltage supply to ECM. Both should read over 9 volts. Terminal "C14" is ignition, and terminal "C16" is constant battery for long term memory.

6. Checks for a bad ground to ECM; terminal "C2" is connected in the ECM.

7. This step distinguishes between a faulty ECM and PROM. Normal response is for DTC 51 to flash, even though the PROM is installed in the ECM. If it doesn't, it means that the ECM is faulty.