DTC Troubleshooting: B1241 (N and A/C ON)
  1. Measure the voltage between body ground and heater control unit connector B (12P) No. 5 and No. 6 terminals individually.
Is there voltage?
YES -
Repair short to power in the wire(s).■
NO -
Go to Step 22 .
  1. Turn the ignition switch to LOCK (0).
  1. Reconnect heater control unit connector B (12P).
  1. Test the power transistor.
Is the power transistor OK?
YES -
Check for loose wires or poor connections at heater control unit connector B (12P) and at the power transistor 4P connector. If the connections are good, substitute a known-good heater control unit, and recheck. If the symptom/indication goes away, replace the original heater control unit .■
NO -
Replace the power transistor.■
  1. Disconnect the jumper wire.
  1. Disconnect the blower motor 2P connector.