78-1

VTM-4 DTC Troubleshooting: 78-1

DTC 78-1:

VTM-4 Control Unit Self-Diagnostic Malfunction

NOTE: Before you troubleshoot, review the general troubleshooting information Reading and Clearing Diagnostic Trouble Codes.

1. Turn the ignition switch to ON (II).

2. Make sure the HDS communicates with the vehicle and the VTM-4 control unit. If it doesn't, troubleshoot the DLC circuit Testing and Inspection.

3. Clear the DTC with the HDS.

4. Start the engine.

5. Check for DTCs with the HDS.

Is DTC 78-1 indicated?

YES -

Go to step 6.

NO -

Intermittent failure, the system is OK at this time.

6. Test the battery Battery Test. Charge or replace the battery if necessary.

7. Turn the ignition switch to ON (II).

8. Check the charging system indicator.

Does the charging system indicator come on, and after the engine starts, does the indicator go off?

YES -

Go to step 9.

NO -

Do the charging system troubleshooting Charging System Indicator Circuit Troubleshooting.

9. Check for installation of any aftermarket CB or Ham radios which may cause an RF signal interference.

Is there an aftermarket radio installed?

YES -

Disconnect the aftermarket radio, and retest.

NO -

Check for poor connections or loose terminals at the VTM-4 control unit connectors. If the connections are OK, substitute a known-good VTM-4 control unit Service and Repair, and recheck. If the symptom/indication goes away with the known-good VTM-4 control unit, replace the original VTM-4 control unit Service and Repair.