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Automatic Temperature Control






B1031-Evaporator Temperature Sensor Circuit Low






For a complete wiring diagram, refer to.

Theory of Operation

The Evaporator Temperature Sensor is a variable resistor that changes in conjunction with temperature, or otherwise known as a thermistor. The Evaporator Temperature Sensor is located in the HVAC housing downstream of the A/C evaporator. The A/C Heater Control module monitors the evaporator temperature by monitoring the voltage change of the Evaporator Temperature Sensor Signal circuit. If the monitored voltage drops below or rises above a predetermined voltage, a DTC will set.

When Monitored: With the ignition on.

Set Condition: The Evaporator Temperature Sensor voltage input to the A/C Heater Control is below 0.01 of a volt for a continuous period of 60 seconds. If the A/C Heater Control detects a valid voltage, the Diagnostic Trouble Code (DTC) will change from active to stored and will stay stored for 100 ignition cycles.






Always perform the HVAC Pre-Diagnostic Troubleshooting procedure before proceeding. Refer to => Non-DTC Based
Diagnostics. HVAC Pre-Diagnostic Troubleshooting Procedure

Test Step 1 - CHECK IF THE DTC IS ACTIVE

Ignition on, engine not running.

Using the scan tool, read HVAC DTCs after 60 seconds.

Is this DTC active?

Yes

Go to Test Step 2 => [ Test Step 2 - CHECK (C21) EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT
FOR A SHORT TO GROUND ]

No

Go to Test Step 5 => [ Test Step 5 - CHECK THE WIRING AND CONNECTORS ]

Test Step 2 - CHECK (C21) EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND







Turn the ignition off to the lock position.

Disconnect the A/C Heater Control harness connector.

Disconnect the Evaporator Temperature Sensor harness connector.

Measure the resistance between ground and the (C21) Evaporator Temperature Sensor Signal circuit.

Is the resistance below 100k Ohms?

Yes

Repair the (C21) Evaporator Temperature Sensor Signal circuit for a short to ground.

Perform the HVAC Verification Test. Refer to => Non-DTC Based Diagnostics. HVAC Verification Test

No

Go to Test Step 3 => [ Test Step 3 - CHECK (C21) EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT
FOR A SHORT TO THE (C121) SENSOR GROUND CIRCUIT ]

Test Step 3 - CHECK (C21) EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO THE (C121) SENSOR GROUND CIRCUIT







Measure the resistance between the (C21) Evaporator Temperature Sensor Signal circuit and the (C121) Sensor Ground circuit.

Is the resistance below 100k Ohms?

Yes

Repair the (C21) Evaporator Temperature Sensor Signal circuit for a short to (C121) Sensor Ground circuit.

Perform the HVAC Verification Test. Refer to => Non-DTC Based Diagnostics. HVAC Verification Test

No

Go to Test Step 4 => [ Test Step 4 - CHECK THE EVAPORATOR TEMPERATURE SENSOR ]

Test Step 4 - CHECK THE EVAPORATOR TEMPERATURE SENSOR

Replace the Evaporator Temperature Sensor.

Perform the HVAC Verification Test. Refer to => Non-DTC Based Diagnostics. HVAC Verification Test

Cycle the ignition off for 30 seconds then back on and wait a minimum of 60 seconds.

With the scan tool read HVAC DTCs.

Does this DTC reset?

Yes

Replace and program the A/C Heater Control.

Perform the HVAC Verification Test. Refer to => Non-DTC Based Diagnostics. HVAC Verification Test

No

Test complete.

Test Step 5 - CHECK THE WIRING AND CONNECTORS

The conditions necessary to set the DTC are not present at this time.

Using the scan tool, check the Environmental Data to help identify the conditions in which the DTC was set.

Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.

Wiggle the wiring and connectors while checking for shorted and open circuits.

Were there any problems found?

Yes

Repair as necessary.

Perform the HVAC Verification Test. Refer to => Non-DTC Based Diagnostics. HVAC Verification Test

No

Test complete.