Engine Control Module: Testing and Inspection

Detailed Component Locations - Electronic Control Unit:

To test the Electronic Control Unit (ECU), located in front of the center console, proceed as follows:

NOTE: Diagnostic memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read.
NOTE: If a sensor connector is disconnected with the ignition switch turned on, the diagnosis code is memorized. In this case, disconnect the battery negative terminal for 15 seconds or more, and all diagnostic memory will be erased.

1. Using the testing procedures extract all malfunction codes.



Diagnosis memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read.

CAUTION: When battery Voltage is low, trouble codes cannot be read. Be sure to check the battery for Voltage and other conditions before starting the test.

2. Does the ECU output a steady 12 VDC at the check connector?
a. If not, and the ECU is suspected to be faulty Test to confirm that the ECU is being supplied with power and ground.
b. If so replacement of the ECU is required.

�Y����ECU Terminal Voltage Chart:

NOTE: Before replacing a ECU that is found to be faulty, insure that no other condition exists that will damage the new unit. This can be best done by testing the inputs and outputs to the ECU for over Voltage/inappropriate power readings or grounds. Use the image in the individual component testing procedures to identify the correct readings for each pin.
Check all pins (at the harness with the ECU removed) that supply a signal to the ECU, for their correct readings and check all other pins to insure that there are no uncalled for Voltage readings or grounds present.

3. Compare all the remaining codes to the following list and perform the required inspections called for in each of the categories that are affected by a code.
Check power supply for:
1. Faulty battery.
2. Faulty fusible link.
3. Faulty fuse.
4. Check for faulty body ground.
Check Fuel supply for:
1. Damaged fuel line.
2. Clogged or damaged fuel filter.
3. Faulty fuel pump.
Check ignition system for:
1. Faulty spark plugs.
2. Faulty ignition wiring.
3. Faulty distributor.
4. Faulty ignition coil.
Check emission control system for:
1. Faulty PCV system.
2. Faulty EGR system.
3. Vacuum leak.
4. Ignition timing and idle speed.
All categories:
ECU system faults are often caused by poor harness contact, therefore check that all of the connectors in all of the affected systems are secure and have continuity.

4. After completing all of the system inspections required in step 3, proceed to the ECU Codes and refer to "Check item (Remedy) column" of the images supplied with "extracting fault codes".

Perform all of the inspections and component tests that are listed for each code that has appeared.



5. If faults were found in step 4, make repairs/replacements as required and clear the fault code from the ECU. Performance test the vehicle against the customer complaint and retest the ECU for fault codes.
1. If the same codes appear retest the repaired/replaced component, If it performs as specified, proceed to step 6.
2. If different fault codes appear, proceed to step 3, and attempt to resolve the new codes.
If NO fault codes were found in step 4, proceed to step 6.

6. If after performing all the required inspections though step 4, NO components were found to be faulty or at step 5 after repairs NO components were found to be faulty, replacement of the ECU is required.

After check and correction of malfunction is completed, disconnect battery ground cable or ECU connector for 15 seconds or more to erase trouble codes. The memory is not erased if power supply is restored within 15 seconds.