DTC B1431: In-Vehicle (Post Evaporator) Temperature Sensor Circuit Short-Circuit

DTC detecting condition: 

In-vehicle sensor circuit is shorted.

Trouble symptom: 

In-vehicle air temperature is falsely recognized as 25°C (77°F), and the compartment temperature is adjusted.

Wiring diagram: 

Air conditioning system Ref. to WIRING SYSTEM>AIR CONDITIONING SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK CONNECTOR  .
   1. Turn the ignition switch to OFF.
   2. Check connecting condition of the A/C control panel connector and in-vehicle sensor connector.

   Is the check result OK?

   Yes:  Go to  2.

   No:  Repair the connector.

2. CHECK DTC  .
   1. Turn the ignition switch to ON.
   2. Read the DTC of [Air Conditioner] using the Subaru Select Monitor. Ref. to AIR CONDITIONER (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1431 displayed? (Current code)

   Yes:  Go to  3.

   No:  Even if DTC is displayed, the circuit has returned to a normal condition at this time.

   Reproduce the failure, and then perform the diagnosis.

   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
3. CHECK IN-VEHICLE SENSOR  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the in-vehicle sensor. Ref. to AIR CONDITIONER>IN-VEHICLE SENSOR (AUTO A/C MODEL)>REMOVAL .
   3. Turn the ignition switch to ON.
   4. Read the DTC of [Air Conditioner] using the Subaru Select Monitor. Ref. to AIR CONDITIONER (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1430 displayed? (Current code)

   Yes:  Replace the in-vehicle sensor. Ref. to AIR CONDITIONER>IN-VEHICLE SENSOR (AUTO A/C MODEL)>REMOVAL .

   No:  Go to  4.

4. CHECK HARNESS (SHORTED BETWEEN LINES AND SHORTED TO GROUND)  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the A/C control panel. Ref. to AIR CONDITIONER>CONTROL PANEL>REMOVAL .
   3. Using a tester, check the continuity between the terminals in the in-vehicle sensor connector and between the in-vehicle sensor connector and chassis ground.

      Connector & terminal 

      (i157) No. 1 - (i157) No. 2:

      (i157) No. 1 - Chassis ground:

   Is there continuity?

   Yes:  Repair or replace the short circuit of the harness.

   No:  Replace the A/C control panel. Ref. to AIR CONDITIONER>CONTROL PANEL>REMOVAL .