HVAC MTC

B1031-EVAPORATOR TEMPERATURE SENSOR CIRCUIT LOW





For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.

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. The sensor thermistor forms the lower half of a voltage divider and the upper half of the voltage divider is provided by a pull up resistor to 5.0 volts. If the monitored voltage drops below or rises above a predetermined voltage, a DTC will set.

- When Monitored:
Continuously with the ignition on.

- Set Condition:
The Evaporator Temperature Sensor voltage input to the A/C Heater Control is less than or equal to 0.01 volts for a continuous period of five seconds. If the A/C Heater Control detects a valid voltage for 10 seconds, the DTC will change from active to stored and will stay stored for 100 consecutive ignition cycles.





Always perform the HVAC Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.

1. CHECK IF THE DTC IS ACTIVE
1. Ignition on, engine not running.
2. With the scan tool, read HVAC DTCs.

Is this DTC active?

Yes

- Go To 2

No

- Go To 5

2. CHECK (C21) EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND




1. Turn the ignition off to the lock position.
2. Disconnect the A/C Heater Control C1 harness connector.
3. Disconnect the Evaporator Temperature Sensor harness connector.
4. 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. HVAC Verification Test.

No

- Go To 3

3. CHECK (C21) EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO (C121) SENSOR GROUND CIRCUIT




1. 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. HVAC Verification Test.

No

- Go To 4

4. CHECK THE EVAPORATOR TEMPERATURE SENSOR
1. Replace the Evaporator Temperature Sensor.
2. Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

Does this DTC reset while performing the Verification Test?

Yes

- Replace and program the A/C Heater Control.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Test complete.

5. CHECK THE WIRING AND CONNECTORS
1. The conditions necessary to set the DTC are not present at this time.
2. With the scan tool, check the Environmental Data to help identify the conditions in which the DTC was set.
3. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
4. Check for an intermittent condition by inspecting the related wiring harness for chafed, pierced, pinched, or partially broken wires.
5. Check the connectors for broken, bent, pushed out, spread, corroded, or contaminated terminals.
6. 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. HVAC Verification Test.

No

- Test complete.