Scan Tool Communication With PCM/ECM Is Not Possible

CIRCUIT OPERATION
- A diagnostic output is made from the 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 PCM (terminal 84) changes to the diagnostic test mode.

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

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




WIRING DIAGRAM




CONNECTORS

DIAGNOSIS







STEP 1. Check the harness wire between the data link connector C-23 and the PCM connector C-41.

NOTE: After inspecting the intermediate connectors C-17 and C-57; inspect the wire. If the intermediate connectors C-17 and C-57 are damaged, repair or replace them. Refer to Harness Connector Inspection >. Then confirm that the malfunction symptom is eliminated.

If the wire between the data link connector C-23 and the PCM connector C-41 is not damaged, go to Step 2.
If the wire between the data link connector C-23 and the PCM connector C-41 is damaged, repair it. Then confirm that the malfunction symptom is eliminated.




STEP 2. Check harness connector C-41 at the PCM for damage.
If harness connector C-41 is damaged, repair or replace it.
Refer to Harness Connector Inspection >.
If harness connector C-41 is normal, refer to INSPECTION PROCEDURE 29 - Power Supply and Ignition Switch-IG System.
Then confirm that the malfunction symptom is eliminated.