ECM Checks

IMPORTANT NOTE!
The ECM is a highly efficient component and replacement is rarely needed. ECM failure is usually caused by another component. If an ECM is found to be faulty, be sure to inspect all input and output circuits prior to installation of the the new ECM. Installing a new ECM without correcting another possible problem will cause repeated ECM failure.

ECM TESTING
The ECM is a transistorized computer component. There are no specific testing procedures. Diagnostic codes 51 and 52 indicate a faulty ECM. Always think of the ECM as the last possible source of a problem. Rarely do they fail.

ECM POWER SUPPLY CIRCUIT CHECK

ECM Power And Ground Supply Circuit:

INSPECTION
- Disconnect the negative battery cable.
- Disconnect the ECM connectors.
- Connect the negative battery cable.
- Turn key ON.
- Check for battery voltage between ECM harness terminals:
12 and ground
21 and ground
33 and ground
- Check for continuity between ECM harness terminals:
11 and ground
20 and ground

RESULTS AND CORRECTION
- If voltage was not present at terminals 12, 21 or 33, check the following:
Main relay
Ignition switch
Fuses
Fuse links
Wiring continuity
- If continuity did not exist between terminals 11 and ground or 20 and ground check the following.
All ECM ground points
Wiring continuity
- If voltage and continuity results were satisfactory, the power and ground circuit to the ECM is OK.