Heater Control Power and Ground Circuit Troubleshooting
  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.■