B1031

B1031-EVAPORATOR TEMPERATURE SENSOR CIRCUIT LOW







Theory of Operation

The Evaporator Temperature Sensor resistance changes in conjunction to temperature. 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.

- When Monitored:
With the ignition on.

- Set Condition:
The Evaporator Temperature Sensor voltage input to the A/C Heater Control is equal to or below 0.01 volts for a continuous period of five 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. HVAC Pre-Diagnostic Troubleshooting Procedure.

1. CHECK IF THE DTC IS ACTIVE
1. Ignition on, engine not running.
2. Using 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 THE (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.
3. Cycle the ignition off for 30 seconds then back on and wait a minimum of 5 seconds.
4. 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. 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. Using the scan tool, check the Environmental Data to help identify the conditions in which the DTC was set.
3. 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.
4. 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.