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

DTC detecting condition: 

Short circuit in the in-vehicle sensor is detected for 3 seconds or more.

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 Refer to WIRING SYSTEM>AIR CONDITIONING SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK CONNECTOR. 
   1. Check the condition of connector connection.
   2. Read the DTC using Subaru Select Monitor. Refer to HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1431 displayed?

   Yes:  Go to  2.

   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 again.

   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
2. CHECK IN-VEHICLE SENSOR. 
   1. Disconnect the in-vehicle sensor. Refer to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>IN-VEHICLE SENSOR (AUTO A/C MODEL)>REMOVAL .
   2. Read the DTC using Subaru Select Monitor. Refer to HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1430 displayed?

   Yes  Replace the in-vehicle sensor. Refer to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>IN-VEHICLE SENSOR (AUTO A/C MODEL)>REMOVAL .

   No:  Go to  3.

3. CHECK HARNESS. 
   1. Turn the ignition switch to ON.
   2. Using the tester, measure the voltage between terminals.

   Connector & terminal 

   (i55) No. 2 (+) - No. 1 (-):

   Is the voltage 4.5 - 5.0 V?

   Yes  Even if DTC is displayed, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.

   No:  Go to  4.

4. CHECK HARNESS (SHORTED BETWEEN LINES). 
   1. Disconnect the connector from the A/C control panel.
   2. Using a tester, check continuity between terminals.

   Connector & terminal 

   (i55) No. 1 - No. 2:

   Is there continuity?

   Yes  Repair or replace the short circuit of the harness.

   No  Replace the A/C control panel. Refer to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>CONTROL PANEL>REMOVAL .