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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 Duct Air Temperature Sensor Signal

B0173 02

B0173 05

B0173 05

1

Lower Left Duct Air Temperature Sensor Signal

B0178 02

B0178 05

B0178 05

1

Air Conditioning Evaporator Temperature Sensor Signal

B3933 02

B3933 05

B3933 05

1

Low Reference

--

B0173 05, B0178 05, 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

The vehicle is turned 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

A default value is used when the DTC is set.

Conditions for Clearing the DTC

    • The DTC will become history if the HVAC control module no longer detects a failure.
    • The history DTC will clear after 100 fault-free ignition cycles.

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 Testing

  1. Vehicle OFF and all vehicle systems OFF, disconnect the harness connector at the appropriate temperature sensor. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 10 Ω between the low reference circuit terminal B and ground.
  3. If 10 Ω or greater
    2.1. Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.
    2.2. Test for less than 2 Ω in the low reference 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 less than 10 Ω
  4. Vehicle in Service Mode.
  5. Verify the scan tool parameter is less than -39°F.
  6. •  Lower Left Duct Air Temperature Sensor
    •  Upper Left Duct Temperature Sensor
    •  A/C Evaporator Temperature Sensor
    If greater than -39°F
    4.1. Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.
    4.2. Test for infinite resistance between the signal circuit terminal A and ground.
    ⇒     If less than infinite resistance, repair the short to ground on the circuit.
    ⇒     If infinite resistance, replace the K33 HVAC control module.
    ⇓   If -39°F or less
  7. Install a 3 A fused jumper wire between the signal circuit and the low reference circuit terminal B.
  8. Verify the scan tool parameter is greater than 240°F.
  9. •  Lower Left Duct Air Temperature Sensor
    •  Upper Left Duct Temperature Sensor
    •  A/C Evaporator Temperature Sensor
    If 240°F or less
    6.1. Vehicle OFF, disconnect the harness connector at the K33 HVAC control module, vehicle in Service Mode.
    6.2. Test for less than 1 V between the signal circuit and ground.
    ⇒     If 1 V or greater, repair the short to voltage on the circuit.
    ⇓     If less than 1 V
    6.3. Vehicle OFF
    6.4. 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 240°F
  10. Test or replace the temperature sensor.

Component Testing

  1. Test the air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
  2. Compare the readings with the Sensor Resistance Table and verify that the resistance is within 5 percent of the specification.
  3. If not within the specified range, replace the sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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


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