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HVAC > HVAC - Manual > Other Information > DTC B3933

DTC B3933

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.

DTC Descriptors

DTC B3933 02: Air Conditioning Evaporator Temperature Sensor Circuit Short to Ground
DTC B3933 05: Air Conditioning Evaporator Temperature Sensor Circuit High Voltage/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 A/C evaporator temperature sensor 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

•  Ignition ON.
•  The HVAC control module is ON.

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 0.1-4.9 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 set.
    ⇒  If a DTC is set

Refer to Circuit/System Testing.     ⇓  If no DTC is set

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 A/C Evaporator Temperature Sensor.     ⇓  If within the specified range

3. All OK.

Circuit/System Testing

1. Ignition OFF, remove the ignition key, open the driver door, disconnect the scan tool and disconnect the harness connector at the B39 A/C Evaporator Temperature Sensor.

Note:  Some control module ground circuits may require up to 20 min to achieve a resistance reading of less than 10 Ω. In most cases the readings will drop below 20 Ω within 1 min indicating the control modules are going to sleep.
2. Test for less than 10 Ω between the B39 A/C Evaporator Temperature Sensor low reference circuit terminal 2 and ground.
    ⇒  If greater than 10 Ω

Repair the open/high resistance in the circuit.     ⇓  If less than 10 Ω

3. Ignition ON, test for 4.8-5.2 V between the B39 A/C Evaporator Temperature Sensor signal circuit terminal 1 and ground.
    ⇒  If less than 4.8 V

  3.1 Ignition OFF, disconnect the X3 harness connector at the K33 HVAC Control Module.
  3.2 Test for infinite resistance between the signal circuit and ground.
⇒  If less than infinite resistance, repair the short to ground on the circuit.
⇓  If infinite resistance
  3.3 Test for less than 2 Ω in the signal circuit end to end.
⇒  If 2 Ω or greater, repair the open/high resistance in the circuit.
⇒  If less than 2 Ω, replace the K33 HVAC Control Module.
    ⇒  If greater than 5.2 V

  3.1 Ignition OFF, disconnect the X3 harness connector at the K33 HVAC Control Module.
  3.2 Ignition ON, test for less than 0.3 V between the signal circuit and ground.
⇒  If greater than 0.3 V, repair the short to voltage on the circuit.
⇒  If less than 0.3 V, replace the K33 HVAC Control Module.
    ⇓  If within 4.8-5.2 V

4. Replace the B39 A/C Evaporator Temperature Sensor and verify the DTC does not reset.
    ⇒  If DTC resets

Replace the K33 HVAC Control Module.     ⇓  If DTC does not reset

5. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•  Control Module References for HVAC control module replacement, programming and setup

HVAC > HVAC - Manual > Other Information > DTC B3933

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