HVAC DTC Troubleshooting: 12
DTC indicator 12: An Open in the Evaporator Temperature Sensor Circuit
1.
Problem verification:

Problem verification
?1.
Turn the ignition switch to LOCK (0) and then back to ON (II).

?2.
Do the Self-Diagnostic Function with the HVAC control unit.

?3.
Check for DTCs.

Is DTC 12 indicated?

     
YES
     
     
     
Go to step 2.
     
NO
     
     
     
Intermittent failure. Check for loose wires or poor connections on the evaporator temperature sensor circuit.?
2.
Open wire check (TEVA line):

Open wire check (TEVA line)
?1.
Turn the ignition switch to LOCK (0).

?2.
Disconnect the following connectors.

?3.
Check for continuity between test points 1 and 2.
Test condition
IG LOCK (0)
HVAC control unit 32P connector: disconnected
Evaporator temperature sensor 2P connector: disconnected
Test circuit
TEVA
Test point 1
HVAC control unit 32P connector No. 32 (RED)
Test point 2
Evaporator temperature sensor 2P connector No. 1 (BRN)


Is there continuity?

     
YES
     
     
     
The TEVA wire is not open. Go to step 3.
     
NO
     
     
     
Repair an open in the wire between the HVAC control unit and the evaporator temperature sensor.?
3.
Open wire check (SENSOR COM/SENS-COM line):

Open wire check (SENSOR COM/SENS-COM line)
?1.
Check for continuity between test points 1 and 2.
Test condition
IG LOCK (0)
HVAC control unit 32P connector: disconnected
Evaporator temperature sensor 2P connector: disconnected
Test circuit
SENSOR COM/SENS-COM
Test point 1
HVAC control unit 32P connector No. 20 (BLU)
Test point 2
Evaporator temperature sensor 2P connector No. 2 (RED)


Is there continuity?

     
YES
     
     
     
The SENSOR COM/SENS-COM wire is OK. Go to step 4.
     
NO
     
     
     
Repair an open in the wire between the HVAC control unit and the evaporator temperature sensor.?
4.
Shorted wire check (TEVA line to S 5V/S5V line):

Shorted wire check (TEVA line to S 5V/S5V line)
?1.
Check for continuity between test points 1 and 2.
Test condition
IG LOCK (0)
HVAC control unit 32P connector: disconnected
Evaporator temperature sensor 2P connector: disconnected
Test circuit
TEVA, S 5V
Test point 1
HVAC control unit 32P connector No. 16 (BLK)
Test point 2
HVAC control unit 32P connector No. 32 (RED)


Is there continuity?

     
YES
     
     
     
Repair a short in the wires between the HVAC control unit and the evaporator temperature sensor.?
     
NO
     
     
     
The TEVA wire and S 5V/S5V wire are OK. Go to step 5.
5.
Evaporator temperature sensor check:

Evaporator temperature sensor check
?1.
Test the evaporator temperature sensor.

Is the evaporator temperature sensor OK?

     
YES
     
     
     
     
NO