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DTC B0173, B0178, or 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 B0173 02: Upper Left Duct Air Temperature Sensor Circuit Short to Ground

DTC B0173 05: Upper Left Duct Air Temperature Sensor Circuit High Voltage/Open

DTC B0178 02: Lower Left Duct Air Temperature Sensor Circuit Short to Ground

DTC B0178 05: Lower Left Duct Air Temperature Sensor Circuit High Voltage/Open

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

Upper Left Outlet Air Temperature Sensor Signal

B0173 02

B0173 05

B0173 05

1

Lower Left Outlet Air Temperature Sensor Signal

B0178 02

B0178 05

B0178 05

1

Evaporator Temperature Sensor Signal

B3933 02

B3933 05

B3933 05

1

Upper Left Outlet Air Temperature Low Reference

-

B0173 05

B0173 05, B0178 05, B3933 05

-

Lower Left Outlet Air Temperature Sensor Low Reference

-

B0178 05

B0173 05, B0178 05, B3933 05

-

Evaporator Temperature Sensor Low Reference

-

B3933 05

B0173 05, B0178 05, B3933 05

-

1. Air Temperature Malfunction

Circuit/System Description

The air temperature sensors are 2-wire negative temperature co-efficient thermistors. The vehicle uses the following air temperature sensors:

    • Air temperature sensor left upper
    • Air temperature sensor left lower
    • 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 +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

Automatic HVAC Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Verify that no DTC is set.
    2. [ARW-LISTFAIL]

  2. If a DTC is present

    Refer to Circuit/System Testing.

    3. [/ARW-LISTFAIL][ARW-LISTPASS]

  3. If no DTC is present

    4. [/ARW-LISTPASS]
  4. Measure actual temperature using a thermometer at each of the duct temperature sensors. Compare this value to the scan tool Duct Actual parameter. The measured temperature should be within 5°C (9°F) difference of Duct Actual parameter value.
    5. [ARW-LISTFAIL]

  5. If not within the specified range

    Replace the duct temperature sensor.

    6. [/ARW-LISTFAIL][ARW-LISTPASS]

  6. If within the specified range

    7. [/ARW-LISTPASS]
  7. 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.
    8. [ARW-LISTFAIL]

  8. If not within the specified range

    Replace the B39 A/C Evaporator Temperature Sensor.

    9. [/ARW-LISTFAIL][ARW-LISTPASS]

  9. If within the specified range

    10. [/ARW-LISTPASS]
  10. All OK.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
  2. Test for less than 5 Ω between the temperature sensor ground circuit terminal B and ground.
    3. [ARW-LISTFAIL]

  3. If greater than 5 Ω

    Repair the open/high resistance in the circuit.

    4. [/ARW-LISTFAIL][ARW-LISTPASS]

  4. If less than 5 Ω

    5. [/ARW-LISTPASS]
  5. Ignition ON, test for 4.8-5.2 V between the signal circuit terminal A and ground.
    6. [ARW-LISTFAIL]

  6. If less than 4.8 V

    7. [/ARW-LISTFAIL]
    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.
    [ARW-LISTFAIL]

  7. If less than infinite resistance, repair the short to ground on the circuit.

    8. [/ARW-LISTFAIL][ARW-LISTPASS]

  8. If infinite resistance

    9. [/ARW-LISTPASS]
    3.3. Test for less than 2 Ω in the signal circuit end to end.
    [ARW-LISTFAIL]

  9. If 2 Ω or greater, repair the open/high resistance in the circuit.

  10. If less than 2 Ω, replace the K33 HVAC Control Module.

    11. [/ARW-LISTFAIL] [ARW-LISTFAIL]

  11. If greater than 5.2 V

    12. [/ARW-LISTFAIL]
    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.
    [ARW-LISTFAIL]

  12. If greater than 0.3 V, repair the short to voltage on the circuit.

  13. If less than 0.3 V, replace the K33 HVAC Control Module.

    14. [/ARW-LISTFAIL] [ARW-LISTPASS]

  14. If within 4.8-5.2 V

    15. [/ARW-LISTPASS]
  15. Replace the temperature sensor and verify the DTC does not reset.
    16. [ARW-LISTFAIL]

  16. If DTC resets

    Replace the K33 HVAC Control Module.

    17. [/ARW-LISTFAIL][ARW-LISTPASS]

  17. If DTC does not reset

    18. [/ARW-LISTPASS]
  18. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Inside Air Temperature Sensor Replacement - Left Side Lower : Right Hand Drive → Left Hand Drive
    •  Air Conditioning Refrigerant Temperature Sensor Replacement - Right Side : Right Hand Drive → Left Hand Drive
    • Control Module References for HVAC control module replacement, setup, and programming
   


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