HVAC - Manual
DTC B0248, B0263, B0408, B0414, B0418, B0424, B3761, or B3770
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC B0248
- Air Flow Control 3 Circuit
DTC B0263
- Air Flow Control 6 Circuit
DTC B0408
- Temperature Control 1 Circuit
DTC B0414
- Range/Performance Temperature Control 2 Feedback Circuit
DTC B0418
- Temperature Control 2 Circuit
DTC B0424
- Range/Performance
DTC B3761
- Air Flow Control 3 Feedback Circuit
DTC B3770
- Air Flow Control 6 Feedback Circuit
Diagnostic Fault Information
Circuit/System Description
The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 5-volt reference source voltage to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions.
* B0414 is for the left air temperature actuator.
* B0424 is for the right air temperature actuator.
* B3761 is for the defrost actuator.
* B3770 is for the mode actuator.
* B0248 is for the defrost actuator.
* B0263 is for the mode actuator.
* B0408 is for the left air temperature actuator.
* B0418 is for the right air temperature actuator.
Conditions for Running the DTC
* The ignition is ON.
* The HVAC module is ON.
Conditions for Setting the DTC
The actual door position differs from the commanded door position by more than 4 counts or the HVAC control module detects the door position signal circuit is less than 3 counts or greater than 253 counts.
Action Taken When the DTC Sets
The control circuit is deactivated for the appropriate actuator.
Conditions for Clearing the DTC
* The DTC becomes history when the HVAC control module no longer detects the condition that set the DTC.
* The history DTC will clear after 50 fault-free ignition cycles.
Circuit/System Verification
Ignition ON, command the appropriate actuator in both directions with a scan tool. The scan tool door position parameter reading should be between 3 and 253 counts.
Circuit/System Testing
1. Ignition OFF, disconnect the appropriate actuator and test for less than 1 ohm between the low reference circuit and ground.
^ If greater than 1 ohm, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
2. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit and ground.
^ If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
^ If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
3. Verify the appropriate scan tool parameter is less than 4 counts.
^ If greater than 4 counts, test the signal circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.
4. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit terminal. Verify the appropriate scan tool parameter is greater than 250 counts.
^ If less than 250 counts, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
5. Ignition ON, verify that a test lamp illuminates between the ignition 3 circuit and ground.
^ If the test lamp does not illuminate, test the ignition 3 circuit for a short to ground an open/high resistance.
6. Install a DMM between the actuator control circuit and ground. While monitoring the DMM use the scan tool to command the appropriate actuator from one direction to the other. If the voltage on the control circuit moves from 0 volts in one direction to 5 volts in the other direction and 2.5 volts in the at rest state.
^ If the voltage does not change, test the control circuit for an open, short to voltage or short to ground. If circuit tests normal replace the HVAC control module.
7. If all circuits test normal, replace the actuator.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Mode Actuator Replacement
* Air Temperature Actuator Replacement - Left Side
* Air Temperature Actuator Replacement - Right Side
* Defroster Actuator Replacement