Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Evaporator Sensor Signal | B3933 14 | 1 | B3933 13 | -- |
Evaporator Low Reference Signal | 1 | 1 | 1 | -- |
Ambient Air Temperature Sensor Signal | B0158 14 | B0158 13 | B0158 13 | 1 |
1. Air Temperature Malfunction | ||||
Circuit/System Description
Air Temperature Sensors
The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:
| • | Ambient air temperature sensor |
| • | A/C evaporator temperature sensor |
A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +101°C (-40 to +215°F). The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the ambient temperature sensor will be displayed on the scan tool. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.
Diagnostic Aids
Condition | Display |
|---|---|
Using Scan Tool Special Function | Updates temperature display instantly |
When the HVAC module MODE, FRONT DEFROST, and REAR DEFROST buttons are pressed simultaneously. | Updates temperature display instantly |
At start up with the engine off less than 2 hours | Displays last stored temperature unless temperature has decreased. The outside air temperature reading is always instantly updated if ambient air temperature has decreased. |
At start up with the engine off more than 2 hours | Displays actual outside temperature |
Vehicle speed above 32 km/h (20 mph) for a minimum of 80 seconds | Updates temperature display at a slow filtered rate |
Vehicle speed above 72 km/h (45 mph) | Displays actual outside temperature |
Sensor ambient temperature reading is less than the last displayed value | Displays actual outside temperature |
When the ambient air decreases. | Updates temperature display rapidly |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Measure actual outside air temperature using a thermometer. Compare this value to the scan tool Outside Air Temp. Raw parameter. The measured temperature should be within 5 degrees of parameter.
- Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. parameter. The measured temperature should be within 5 degrees of parameter.
- Measure actual temperature using a thermometer at the A/C evap. temperature sensor. Compare this value to the scan tool A/C Evap. Temperature Sensor parameter. The measured temperature should be within 5 degrees of the parameter.
| ⇒ | If not within the specified range, refer to Ambient / Inside Air Temperature Sensor Circuit Malfunction. |
| ⇒ | If not within the specified range, refer to Ambient Temperature Sensor Circuit Malfunction. |
| ⇒ | If not within the specified range, refer to Evaporator Temperature Sensor Circuit Malfunction. |
Ambient Temperature Sensor Circuit Malfunction
- Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
- Test for less than 1 ohm between the low reference circuit terminal B and ground.
- Ignition ON, verify the appropriate scan tool Temp Sensor Voltage parameter is greater than 4.9 volts or 250 counts.
- Install a 3-amp fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Temp Sensor Voltage parameter is less than 0.1 volt or 5 counts.
- If all circuits test normal, test or replace the appropriate temperature sensor.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If less than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
Evaporator Temperature Sensor Circuit Malfunction
- Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
- Test for less than 1.0 ohm between the low reference circuit terminal 2 and ground.
- Ignition ON, verify the appropriate Temperature Sensor parameter is greater than 4.9 volts or 250 counts.
- Install a 3-amp fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the Scan Tool Temperature Sensor parameter is less than 0.1 volt or 5 counts.
- If all circuits test normal, test or replace the appropriate temperature sensor.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If less than the specified range, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
Component Testing
- Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
- Test for the appropriate resistance between the signal terminal A or 1 and the low reference terminal B or 2. Refer to Sensor Resistance Table for resistance values.
| ⇒ | If not within the specified range, replace the appropriate sensor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
