Diagnostic Instructions

DTC Descriptor

DTC B3933 02: Air Conditioning Evaporator Temperature Sensor Circuit Short to Ground

DTC B3933 05: Air Conditioning Evaporator Temperature Sensor Circuit Short to Battery or Open

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Evaporator Temperature Sensor Signal	B3933 02	B3933 05	B3933 05	1
Evaporator Temperature Sensor Low Reference	--	B3933 05	B3933 05	--
1. Air Temperature Malfunction

Circuit/System Description

The evaporator temperature sensors is a 2-wire negative temperature co-efficient thermistor. 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 +85°C (-40 to +185°F). The sensor signal varies between 0-5 V. 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 detects a malfunctioning sensor, then the control module software will use a default air temperature value. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

Conditions for Running the DTC

Conditions for Setting the DTC

The HVAC control module detects the sensor signal out of range. The signal voltage is less than 0.1 V or greater than 4.9 V for more than 50 ms.

Action Taken When the DTC Sets

The system operates using a default value.

Conditions for Clearing the DTC

The sensor signal is within specified range between 0.1 V and 4.9 V.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Verify that no DTC is present.

⇒	If a DTC is present, refer to Circuit/System Testing.

2. Measure actual evaporator temperature using a thermometer. Compare this value to the scan tool A/C Evaporator Temperature Sensor parameter. The measured temperature should be within 5°C (9°F) difference of parameter value.

⇒	If not within the specified range, replace the B39 Evaporator Temperature Sensor.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B39 Evaporator Temperature Sensor.
2. Test for less than 5 Ω between the B39 Evaporator Temperature Sensor ground circuit terminal 1 and ground.

⇒	If greater than the specified value, test the ground circuit for an open/high resistance.

3. Ignition ON, test for 4.8-5.2 V between the B39 Evaporator Temperature Sensor signal circuit terminal 2 and ground.

⇒	If less than the specified range, test the signal circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the K33 HVAC Control Module.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K33 HVAC Control Module.

4. If all circuits test normal, replace the B39 Evaporator Temperature Sensor and verify the DTC does not reset.

⇒	If the DTC resets, replace the K33 HVAC Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.