Heater Control Power and Ground Circuit Troubleshooting
  1. Check the No. 16 (7.5 A) fuse in the driver's under-dash fuse/relay box.
Is the fuse OK?
YES -
Go to Step 2 .
NO -
Replace the fuse, and recheck.■
  1. Disconnect heater control unit connector A (28P).
  1. Turn the ignition switch to ON (II).
  1. Measure the voltage between heater control unit connector A (28P) No. 9 terminal and body ground.
Is there battery voltage?
YES -
Go to Step 5 .
NO -
Repair open in the wire between the No. 16 (7.5 A) fuse in the driver's under-dash fuse/relay box and the heater control unit.■
  1. Turn the ignition switch to LOCK (0).
  1. Disconnect heater control unit connector B (12P).
  1. Check for continuity between heater control unit connector B (12P) No. 3 terminal and body ground.
Is there continuity?
YES -
Check for loose wires or poor connections at heater control unit connector B (12P). If the connections are good, substitute a known-good heater control unit, and recheck. If the symptom/indication is still present, substitute a known-good heater control unit, and recheck.■
NO -
Check for an open in the wire between the heater control panel and body ground. If the wire is OK, check for poor ground at G401.■