Scan Tool Communication With ECM/PCM Not Possible

Data Link Connector Circuit:

CIRCUIT OPERATION
- A diagnostic output is made from the ECM (terminal 62) or PCM (terminal 85) to the diagnostic output terminal (terminal 7) of the data link connector.
- When diagnostic test mode control terminal (terminal 1) of the data link connector is grounded, the ECM (terminal 56) or PCM (terminal 84) changes to the diagnostic test mode.

COMMENT
One of the following causes may be suspected:
- No power supply to ECM or PCM.
- Defective ground circuit of ECM or PCM.
- Defective ECM or PCM.
- Improper communication line between ECM or PCM and scan tool.

TROUBLESHOOTING HINTS
The most likely causes for this case:
- Malfunction of ECM power supply circuit .
- Malfunction of PCM power supply circuit .
- Malfunction of the ECM .
- Malfunction of PCM .
- Open circuit between ECM and data link connector .
- Open circuit between PCM and data link connector .
DIAGNOSIS

STEP 1. Check the harness wire between data link connector C-29 and ECM connector C-56 or PCM connector C-57 .

NOTE: After Inspecting intermediate connectors C-28 and C-77, inspect the wire. If intermediate connectors C-28 and C-77 are damaged, repair or replace them. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

If the wire between data link connector C-29 and ECM connector C-56 or PCM connector C-57 is not damaged, go to Step 2.

If the wire between data link connector C-29 and ECM connector C-56 or PCM connector C-57 is damaged, repair it. Then confirm that the malfunction symptom is eliminated.

STEP 2. Check harness connector C-56 at the ECM or harness connector C-57 for damage.
If harness connector C-56 or C-57 is normal, refer to INSPECTION PROCEDURE 30 - Power Supply System and Ignition Switch-IG System.

If harness connector C-56 or C-57 is damaged, repair or replace it. Refer to Harness Connector Inspection.

Then confirm that the malfunction symptom is eliminated.