Code A-2: No ALDL Data Or No Code 12 "Check Engine" Light On Steady
There should always be a steady "CHECK ENGINE" light when the ignition is on and engine stopped. With the diagnostic terminal grounded, the light should flash a Code 12, followed by any trouble codes stored in memory. A steady light could be a short to ground in the light control circuit No. 03, or an open in diagnostic circuit No. 451.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- If there is problem with the ECM that causes a "Scan" tester to not read serial data, ECM should not flash a Code 12. If Code 12 does flash, be sure that the "Scan" tester is working properly on another vehicle. If the "Scan" tester is functioning properly and circuit No. 461 (serial data) is okay, the PROM/MEM-CAL or ECM may be at fault for the "NO ALDL".
- If the light goes off when the ECM connector is disconnected, then circuit No. 03 is not shorted to ground.
- This test will check for an open diagnostic circuit No. 451 (diagnostic enable).
- At this point, the "CHECK ENGINE" light wiring is okay. The problem is a faulty ECM or PROM/MEM-CAL. If Code 12 does not flash, ECM should be replaced using the original PROM/MEM-CAL. Replace the PROM/MEM-CAL only after trying an ECM, as a defectivePROM/MEM-CAL is an unlikely cause of the problem.