( TF09E8HK711000Y1231FAAT00 )
DTC Troubleshooting: B1231 (G and AUTO)
DTC B1231 or DTC indicator G and AUTO:
 An Open in the Evaporator Temperature Sensor Circuit
  1. Clear the DTC with the HDS.
  1. Turn the ignition switch to LOCK (0), and then to ON (II).
  1. Check for DTCs.
Is DTC B1231 or G and AUTO indicated?
YES -
Go to Step 5 .
NO -
Intermittent failure, check for loose wires or poor connections on the evaporator temperature sensor circuit.■
  1. Turn the ignition switch to LOCK (0).
Is the evaporator temperature sensor OK?
YES -
Go to Step 7 .
NO -
Replace the evaporator temperature sensor .■
  1. Jump the SCS line with the HDS.
    NOTE: This step must be done to protect the engine control module (ECM)/powertrain control module (PCM) from damage.
  1. Disconnect ECM/PCM connector A (49P).
  1. Check for continuity between the following terminals of ECM/PCM connector A (49P) and the evaporator temperature sensor 2P connector.
    49P:
    2P:
    No. 10
    No. 2
    No. 38
    No. 1

Is there continuity?
YES -
Go to Step 10 .
NO -
Repair open in the wire(s) between the ECM/PCM and the evaporator temperature sensor.■
  1. Check for continuity between the climate control unit 36P connector No. 23 terminal and the evaporator temperature sensor 2P connector No. 1 terminal.
Is there continuity?
YES -
Go to Step 11 .
NO -
Repair open in the wire between the climate control unit and the evaporator temperature sensor.■
  1. Reconnect ECM/PCM connector A (49P).
  1. Reconnect the climate control unit 36P connector.
  1. Turn the ignition switch to ON (II).
  1. Measure the voltage between the climate control unit 36P connector No. 23 terminal and body ground.
Is there about 4.30−5.25 V?
YES -
Check for loose wires or poor connections at ECM/PCM connector A (49P). If the connections are good, substitute a known-good ECM/PCM and recheck the original climate control unit.■
NO -
Substitute a known-good climate control unit, and recheck. If the symptom/indication goes away, replace the original climate control unit .■