Heater Control Power and Ground Circuit Troubleshooting (Without A/C)

Heater Control Power and Ground Circuit Troubleshooting

1. Check the No. 54 (30 A) fuse in the main under-hood fuse/relay box, and the No. 20 (7.5 A) and No. 25 (7.5 A) fuses in the under-dash fuse/relay box.

Are the fuses OK?
YES - Go to step 2.

NO - Replace the fuse(s), and recheck. If the fuse(s) blow again, check for a short in the No. 54 (30 A), the No. 20 (7.5 A), and the No. 25 (7.5 A) fuse circuits.


2. Disconnect the heater control panel 30P connector.

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

4. Measure the voltage between heater control panel 30P connector terminal No. 30 and body ground.

Is there battery voltage?
YES - Go to step 5.

NO - Repair open in the wire between the No. 20 (7.5 A) fuse in the under-dash fuse/relay box and the heater control panel.






5. Turn the ignition switch to LOCK (0).

6. Measure the voltage between heater control panel 30P connector terminal No. 29 and body ground.

Is there battery voltage?
YES - Go to step 7.

NO - Repair open in the wire between the No. 25 (7.5 A) fuse in the under-dash fuse/relay box and the heater control panel.






7. Check for continuity between heater control panel 30P connector terminal No. 26 and body ground.

Is there continuity?
YES - Check for loose wires or poor connections at the heater control panel 30P connector. If the connections are good, substitute a known-good heater control panel, and recheck. If the symptom/indication goes away, replace the original heater control panel.

NO - Check for an open in the wire between the heater control panel and body ground. If the wire is OK, check for poor body ground at G402.