HVAC Systems - Automatic: Diagnosis Chevrolet Tahoe II

Scan Tool Output Controls

ECC Scan Tool Output Controls

PCM Scan Tool Output Controls

Scan Tool Data List

HVAC Scan Tool Data List

PCM Scan Tool Data List

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The HVAC control module monitors the outside ambient air temperature via an ambient air temperature sensor. When the air is cold, the sensor resistance voltage and the signal voltage are high. When the air is warm, the sensor resistance voltage and the signal voltage are low.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control module detects that the signal circuit is out of the range 0.09-5.0 volts.

Action Taken When the DTC Sets

A default value will be used for the sensor data by the HVAC control module. The sensor reading, which displays on the scan tool in the HVAC data list, will be the default value.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects a condition.
2. The history DTC clears after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The HVAC control module monitors the passenger compartment inside air temperature through an inside air temperature sensor assembly. When the air is cold, the sensor resistance and the signal voltage are high. When the air is warm, the sensor resistance and the signal voltage are low.

The ignition is turned ON.

The HVAC control module detects the signal circuit is out of the range 0.09-5.0 volts.

A default value will be used for the sensor data by the HVAC control module. The sensor reading, which displays on the scan tool in the HVAC data list, will be this default value.

1. The DTC will become history if the HVAC control module no longer detects a condition.
2. The history DTC clears after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The HVAC control module monitors the air temperature in the upper center A/C discharge duct via an upper air temperature sensor. When the air is cold, the sensor resistance and the signal voltage are high. When the air is warm, the sensor resistance and the signal voltage are low.

The ignition is turned ON.

The HVAC control module detects the signal circuit is less than 5 Counts (0.09 V) or greater than 250 Counts (4.90 V).

A default value will be used for the sensor data by the HVAC control module. The actual value of the sensor will be displayed on the scantool.

1. The DTC will become history if the HVAC control module no longer detects a condition.
2. The history DTC clears after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The HVAC control module monitors the air temperature in the floor discharge duct via a lower air temperature sensor. When the air is cold, the sensor resistance and the signal voltage are high. When the air is warm, the sensor resistance and the signal voltage are low.

The ignition is turned ON.

The HVAC control module detects the signal circuit is less than 5 Counts (0.09 V) or greater than 250 Counts (4.90 V).

A default value will be used for the sensor data by the HVAC control module. The actual value of the sensor will be displayed on the scan tool.

1. The DTC will become history if the HVAC control module no longer detects a condition.
2. The history DTC clears after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The HVAC control module monitors the ambient light via a sunload sensor. The HVAC control module uses this information in order to modify the effect of the sun on the vehicle inside air temperature. When the sensor is in direct sunlight, the signal voltage is low. When the sensor is covered, the signal voltage is high.

The ignition is turned ON.

The HVAC control module detects the signal circuit is out of the range 0.09-5.0 volts.

A default value will be used for the sensor data by the HVAC control module. The sensor reading, which displays on the scan tool in the HVAC data list, will be this default value.

1. The DTC will become history if the HVAC control module no longer detects a condition.
2. The history DTC clears after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The recirculation actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The HVAC control module controls the recirculation door position by sending a control signal to the actuator. The signal's value is dependent upon the desired mode selected by the vehicle occupants. As the recirculation actuator moves, the potentiometer produces the actual door position signal that is sent to the HVAC control module. The HVAC control module continues to command the actuator to move until the desired and actual values are equal.

After a calibration or recalibration procedure is performed, the HVAC control module calculates the recirculation actuator travel range. The HVAC control module commands the actuator through it's full range. The HVAC control module stores the learned minimum and maximum position values. The travel range value is calculated by subtracting the minimum and maximum position values. The HVAC control module compares the travel range, minimum and maximum values to calibrated value ranges. If the travel range value is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful. The HVAC control module continuously compares the actual actuator position to the calibrated minimum and maximum position values.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. The HVAC control module keep alive memory battery power must be interrupted to run the range check (recalibration procedure).

1. Recirculation actuator position signal is less than 5 counts.
2. Recirculation actuator position signal is more than 250 counts.
3. The recirculation actuators total travel range (min-max) is less than or greater than the calibrated limits.

1. The DTC is stored in DTC information.
2. The HVAC control module will continue to make use of whatever travel range is still available.

1. If the HVAC control no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. A short to voltage on the 5-volt reference circuit of the recirculation actuator will cause DTC B0229 and DTC B0414 to set.
2. A damaged or broken recirculation door and or actuator can cause this DTC to set.
3. The range fault can only be detected following a check of the actuator travel range. The actuator travel range check (recalibration procedure) can only be initiated by disrupting power to the HVAC control module.

The mode actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The HVAC control module controls the mode door position by sending a control signal to the actuator. The signal's value is dependent upon the desired mode selected by the vehicle occupants. As the actuator moves, the potentiometer produces the actual door position signal that is sent to the HVAC control module. The HVAC control module continues to command the actuator to move until the desired and actual values are equal. The door directs airflow through the outlets as selected by the vehicles occupants.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. An mode actuator positional change is attempted.

The actual mode door position differs from the commanded mode door position by 4 counts or more.

The mode actuator is considered stalled and the HVAC control module will command the mode actuator to stop rotation (2.5 V).

1. If the HVAC control no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. A dead zone exists in a range 10 counts above or below the mode door max or mode door min positions. When the mode door actual data parameter is within the dead zone, the DTC will not set. If the mode door commanded data parameter differs from the mode door actual data parameter by 4 counts or more outside the dead zone, the DTC will set.
2. A damaged or broken mode door and or actuator can cause this DTC to set.

DTC B0248

The recirculation actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The HVAC control module controls the recirculation door position by sending a control signal to the actuator. The signal's value is dependent upon the desired mode selected by the vehicle occupants. As the actuator moves, the potentiometer produces the actual door position signal that is sent to the HVAC control module. The HVAC control module continues to command the actuator to move until the desired and actual values are equal. The door directs airflow through the outlets as selected by the vehicles occupants.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. A recirculation actuator positional change is attempted.

The actual recirculation door position differs from the commanded recirculation door position by 4 counts or more.

The recirculation actuator is considered stalled and the HVAC control module will command the mode actuator to stop rotation (2.5 V).

1. If the HVAC control module no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. A dead zone exists in a range 10 counts above or below the recirculation door max or recirculation door min positions. When the recirculation door actual data parameter is within the dead zone, the DTC will not set. If the recirculation door commanded data parameter differs from the recirculation door actual data parameter by 4 counts or more outside the dead zone, the DTC will set.
2. A damaged or broken recirculation door and or actuator can cause this DTC to set.

DTC B0268

The air temperature actuator is an electronic device that incorporates a stepper motor and a feedback potentiometer. The HVAC control module determines the position of the air temperature actuator from the voltage on the potentiometer. When the air temperature changes by greater than 4 counts, the control module performs the following functions

1. Drives the air temperature actuator in the appropriate direction in order to achieve the desired setting
2. Compares the actual position to the commanded position

If the actual value differs from the commanded value by 4 or more counts, the actuator is stalled, and the DTC will set.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. An actuator change in position is attempted.

The actual position of the air mix door differs from the commanded position by at least 4 counts.

The actuator is stalled, and the HVAC control module will command the actuator to stop rotation.

1. If the HVAC control no longer detects a condition, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a condition.
3. The DTC can be cleared with a scan tool.

1. A dead zone exists in a range 10 counts above the mix door maximum position to 10 counts below the mix door minimum position. When the air mix door actual data parameter is within the dead zone, the DTC will not set. If the commanded data parameter differs from the actual data parameter by 4 or more counts outside the dead zone, the DTC will set.
2. A damaged air temperature door, a damaged actuator, a broken air temperature door, or a broken actuator can cause this DTC to set.
3. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

The air temperature actuator is an electronic device that incorporates a stepper motor and a feedback potentiometer. The HVAC control module determines the position of the air temperature actuator that is based on the voltage from the potentiometer. When the keep alive RAM memory, the battery positive voltage circuit, of the HVAC control module is interrupted, the module will calibrate the actuators. The HVAC control module performs a travel range comparison of the determined values of the actuator to the calibrated values within the HVAC control module. If the determined range does not equal the calibrated expected range, the actuator will be considered not calibrated, and the DTC will set. The HVAC control module will also perform a continuous test on the current feedback value. If the feedback value does not fall within the calibrated range, the DTC will set.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. The battery positive voltage circuit, which provides keep alive RAM memory power, of the HVAC control module must be interrupted in order to run the recalibration. This includes disconnecting the battery, removal of the Radio fuse and disconnecting the HVAC control module.

1. The position signal of the air temperature door is out of the range 0.09-4.0 volts (5-250 counts).
2. The total travel range of the air temperature actuator falls without the calibrated limits.

1. The HVAC control module will continue to make use of whatever travel range is still available.
2. Each time the ignition switch is turned ON, the HVAC control module retests the actuator travel range.

1. If the HVAC control module no longer detects a condition, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a condition.
3. The DTC can be cleared with a scan tool.

1. The range fault can only be detected following a recalibration. The recalibration can only be initiated by removing the battery positive voltage circuit to the HVAC control module.
2. The calibration limit is 64-216 counts. An actual range below this limit suggests an obstruction, something stuck in the door which limits travel. An actual range above this limit suggests an excessive travel condition, damaged, or missing foam seals.
3. A damaged air temperature door or a damaged actuator can cause this DTC to set.
4. An intermittent short to ground on the HVAC class 2 serial data circuit can set this DTC. Recalibrate actuators and test system.
5. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

The auxiliary air temperature actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The position of the auxiliary air temperature actuator is based on the auxiliary air temperature door position signal voltage from the potentiometer. The rear auxiliary HVAC module converts this voltage to a digital signal that can be transmitted over the keyboard display driver (KDD) data bus to the HVAC control module. The HVAC control module contains the logic that controls the operation of the auxiliary air temperature actuator. When a change in air temperature is required (greater than 4 counts) the HVAC control module will drive the air temperature actuator in the appropriate direction to achieve the desired setting while comparing the actual position to the commanded position. If the actual value differs from the commanded value by 4 or more counts, the actuator is considered stalled and the DTC will set.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. An actuator positional change is attempted.

The actual air mix door position differs from the commanded air mix door position by 4 counts or more.

The actuator is considered stalled and the HVAC control module will command the actuator to stop rotation (2.5 V).

1. If the HVAC control no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. A dead zone exists in a range 10 counts above or below the mix door max or mix door min positions. When the air mix door actual data parameter is within the dead zone, the DTC will not set. If the air mix door commanded data parameter differs from the air mix door actual data parameter by 4 counts or more outside the dead zone, the DTC will set.
2. A damaged or broken auxiliary air temperature door and or actuator can cause this DTC to set.
3. If condition not present refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

The auxiliary air temperature actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The position of the auxiliary air temperature actuator is based on the auxiliary air temperature door position signal voltage from the potentiometer. The auxiliary HVAC module converts this voltage to a digital signal that can be transmitted over the keyboard display driver (KDD) data bus to the HVAC control module. The HVAC control module contains the logic that controls the operation of the auxiliary air temperature actuator. When the keep alive RAM memory, the battery positive voltage circuit, of the HVAC control module is interrupted, the module will calibrate the actuators. The HVAC control module will perform a travel range comparison of the calculated minimum and maximum extremes of the actuator to the calibrated minimum and maximum range extremes within the HVAC control module. If the calculated range does not equal the calibrated expected range the actuator will be considered not calibrated and the DTC will set. The HVAC control module will also perform a continuous test on the current feedback value. If the feedback value does not equal or fall within the calibrated range the DTC will set.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. The battery positive voltage circuit, which provides keep alive RAM memory power, of the HVAC control module must be interrupted in order to run the recalibration. This includes disconnecting the battery, removal of the Radio fuse and disconnecting the HVAC control module.

1. The auxiliary air temperature door position signal is less than 5 counts or greater than 250 counts.
2. The auxiliary air temperature actuators total travel range (max-min) is less than or greater than the calibrated limits.

1. The HVAC control module will continue to make use of whatever travel range is still available.
2. Each time the ignition switch is turned ON the HVAC control module will recheck the actuator travel range.

1. If the HVAC control no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. The range fault can only be detected following a recalibration. The recalibration can only be initiated by removing the battery positive voltage circuit to the HVAC control module.
2. The calibration limit is 64-216 counts. An actual range below this limit suggests an obstruction, something stuck in the door limiting travel. An actual range above this limit suggests an over travel condition, damaged or missing foam seals.
3. A damaged or broken auxiliary air temperature door and or actuator can cause this DTC to set.
4. If condition not present refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

DTC B0434

This DTC is an indication of a malfunction with the Infrared thermistor which is internal to the rear auxiliary control module.

The ignition is turned ON.

1. This test checks the value of the Infrared thermistor (part of the Rear Aux ECC module) and the stored thermistor values. If the stored values are above or below the system specifications, the DTC will be set.
2. The above conditions are present for 3 consecutive failures.

1. The automatic portion of the heater and A/C system will be disabled.
2. A calibrated (failsoft) value of 75 degrees will be used in all HVAC calculations requiring the temperature of the rear passenger compartment.

1. The DTC will become history if the HVAC Module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

DTC B1020

The auxiliary mode actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The auxiliary HVAC control module control assemblies; control the auxiliary mode door position by sending a control signal to the actuator. The signal's value is dependent upon the desired mode selected by the vehicle occupants. As the actuator moves, the potentiometer produces the actual door position signal that is sent to the rear auxiliary HVAC control module. The rear auxiliary HVAC control module continues to command the actuator to move until the desired and actual values are equal. The door directs airflow through the outlets as selected by the vehicles occupants.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. An auxiliary mode actuator positional change is attempted.

The actual auxiliary mode door position differs from the commanded auxiliary mode door position by 4 counts or more.

The auxiliary mode actuator is considered stalled and the HVAC control module will command the auxiliary mode actuator to stop rotation (2.5 V).

1. If the rear auxiliary HVAC control module no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. A dead zone exists in a range 10 counts above or below the auxiliary mode door max or auxiliary mode door min positions. When the auxiliary mode door actual data parameter is within the dead zone, the DTC will not set. If the auxiliary mode door commanded data parameter differs from the auxiliary mode door actual data parameter by 4 counts or more outside the dead zone, the DTC will set.
2. A damaged or broken auxiliary mode door and or actuator can cause this DTC to set.

DTC B3531

The auxiliary HVAC control module monitors the air temperature in the upper auxiliary discharge duct via an upper auxiliary air temperature sensor. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low. The auxiliary HVAC control module converts this voltage to a digital signal that can be transmitted over the keyboard display driver (KDD) data bus to the HVAC control module. The HVAC control module contains the logic that monitors the auxiliary air temperature and is responsible for setting the DTC.

The ignition is turned ON.

The auxiliary HVAC control module detects the signal circuit is less than 5 Counts (0.09 V) or greater than 250 Counts (4.90 V).

A default value will be used for the sensor data by the HVAC control module. The actual value of the sensor will be displayed on the scantool.

1. The DTC will become history if the auxiliary HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Check the following conditions

1. Visually inspect the sensor for contamination or damage.
2. Verify that air flow to sensor is not restricted.
3. Verify that the sensor is installed properly.
4. If condition not present refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

The auxiliary HVAC control module monitors the air temperature in the lower auxiliary discharge duct via a lower auxiliary air temperature sensor. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low. The auxiliary HVAC control module converts this voltage to a digital signal that can be transmitted over the keyboard display driver (KDD) data bus to the HVAC control module. The HVAC control module contains the logic that monitors the auxiliary air temperature and is responsible for setting the DTC.

The ignition is turned ON.

The auxiliary HVAC control module detects the signal circuit is less than 5 Counts (0.09 V) or greater than 250 Counts (4.90 V).

A default value will be used for the sensor data by the HVAC control module. The actual value of the sensor will be displayed on the scan tool.

1. The DTC will become history if the auxiliary HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Check the following conditions

1. Visually inspect the sensor for contamination or damage.
2. Verify that air flow to sensor is not restricted.
3. Verify that the sensor is installed properly.
4. If condition not present refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

The mode actuator is an electronic device that incorporates a stepper motor and a feedback potentiometer. The HVAC control module determines the position of the mode actuator that is based on the voltage from the potentiometer. When the keep alive RAM memory, the battery positive voltage circuit, of the HVAC control module is interrupted, the module will calibrate the actuators. The HVAC control module performs a travel range comparison of the determined values of the actuator to the calibrated values within the HVAC control module. If the determined range does not equal the calibrated expected range, the actuator will be considered not calibrated, and the DTC will set. The HVAC control module will also perform a continuous test on the current feedback value. If the feedback value does not fall within the calibrated range, the DTC will set.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. The battery positive voltage circuit, which provides keep alive RAM memory power, of the HVAC control module must be interrupted in order to run the recalibration. This includes disconnecting the battery, removal of the Radio fuse and disconnecting the HVAC control module.

1. The position signal of the mode door is out of the range 0.09-4.0 volts (5-250 counts).
2. The total travel range of the mode actuator falls without the calibrated limits.

1. The HVAC control module will continue to make use of whatever travel range is still available.
2. Each time the ignition switch is turned ON, the HVAC control module retests the actuator travel range.

1. If the HVAC control no longer detects a condition, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a condition.
3. The DTC can be cleared with a scan tool.

1. The range fault can only be detected following a recalibration. The recalibration can only be initiated by removing the battery positive voltage circuit to the HVAC control module.
2. The calibration limit is 64-216 counts. An actual range below this limit suggests an obstruction, something stuck in the door which limits travel. An actual range above this limit suggests an excessive travel condition, damaged, or missing foam seals.
3. A damaged mode door or a damaged actuator can cause this DTC to set.
4. An intermittent short to ground on the HVAC class 2 serial data circuit can set this DTC. Recalibrate actuators and test system.
5. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

DTC B3761

The auxiliary mode actuator is an electronic device that incorporates a stepper motor and a feedback potentiometer. The HVAC control module determines the position of the auxiliary mode actuator that is based on the voltage from the potentiometer. When the keep alive RAM memory, the battery positive voltage circuit, of the HVAC control module is interrupted, the module will calibrate the actuators. The HVAC control module performs a travel range comparison of the determined values of the actuator to the calibrated values within the HVAC control module. If the determined range does not equal the calibrated expected range, the actuator will be considered not calibrated, and the DTC will set. The HVAC control module will also perform a continuous test on the current feedback value. If the feedback value does not fall within the calibrated range, the DTC will set.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. The battery positive voltage circuit, which provides keep alive RAM memory power, of the HVAC control module must be interrupted in order to run the recalibration. This includes disconnecting the battery, removal of the Radio fuse and disconnecting the HVAC control module.

1. The position signal of the auxiliary mode door is out of the range 0.09-4.0 volts (5-250 counts).
2. The total travel range of the auxiliary mode actuator falls without the calibrated limits.

1. The HVAC control module will continue to make use of whatever travel range is still available.
2. Each time the ignition switch is turned ON, the HVAC control module retests the actuator travel range.

1. If the HVAC control no longer detects a condition, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a condition.
3. The DTC can be cleared with a scan tool.

1. The range fault can only be detected following a recalibration. The recalibration can only be initiated by removing the battery positive voltage circuit to the HVAC control module.
2. The calibration limit is 64-216 counts. An actual range below this limit suggests an obstruction, something stuck in the door which limits travel. An actual range above this limit suggests an excessive travel condition, damaged, or missing foam seals.
3. A damaged auxiliary mode door or a damaged actuator can cause this DTC to set.
4. An intermittent short to ground on the HVAC class 2 serial data circuit can set this DTC. Recalibrate actuators and test system.
5. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-175720-S15006521422005042600000) .

DTC B3764

The HVAC control module communicates with the auxiliary HVAC control module through the HVAC control module data signal and HVAC control module clock signal circuits. This communication link is only used by the HVAC control module and the auxiliary HVAC control module to exchange HVAC data.

The ignition is turned ON.

There is a loss of communications between the HVAC control module and the auxiliary HVAC control module.

The auxiliary HVAC control module will lose all automatic control.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175720-S08180388062005042600000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. Verify that the customer is using the correct key to enable personalization and is not inadvertently activating auxiliary HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(ref-190277-S37762598012005091400000) .
6. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
7. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «HVAC Compressor Clutch Does Not Engage»(ref-190277-S23004865652005091400000)
2. «HVAC Compressor Clutch Does Not Disengage»(ref-190277-S25357607092005091400000)
3. «Blower Motor Always On»(ref-190277-S12925340632005091400000)
4. «Blower Motor Inoperative»(ref-190277-S10371447102005091400000)
5. «Blower Motor Malfunction»(ref-190277-S12310045332005091400000)
6. «Blower Motor Always On - Auxiliary (W/O Sunroof)»(ref-190277-S06219083752005091400000) or «Blower Motor Always On - Auxiliary (W/Sunroof or Heat Only)»(ref-190277-S03864097292005091400000)
7. «Blower Motor Always On - Auxiliary (W/O Sunroof)»(ref-190277-S06219083752005091400000) or «Blower Motor Always On - Auxiliary (W/Sunroof or Heat Only)»(ref-190277-S03864097292005091400000)
8. «Blower Motor Always On - Auxiliary (W/O Sunroof)»(ref-190277-S06219083752005091400000) or «Blower Motor Always On - Auxiliary (W/Sunroof or Heat Only)»(ref-190277-S03864097292005091400000)
9. «Too Hot in Vehicle»(ref-190277-S35750200352005091400000)
10. «Too Cold in Vehicle»(ref-190277-S41099110102005091400000)
11. «Too Hot in Vehicle - Auxiliary (w/o Sunroof)»(ref-190277-S25474871022005091400000) or «Too Hot in Vehicle - Auxiliary (w/ Sunroof)»(ref-190277-S11514291472005091400000)
12. «Too Cold in Vehicle - Auxiliary (w/o sunroof)»(ref-190277-S02839746052005091400000) or «Too Cold in Vehicle - Auxiliary (w/ sunroof)»(ref-190277-S02287539832005091400000)
13. «Outside Air Temperature Display Inaccurate or Inoperative»(ref-190277-S06258360752005091400000)
14. «Air Delivery Improper»(ref-190277-S02895416482005091400000)
15. «Air Delivery Improper - Auxiliary (W/O Sunroof)»(ref-190277-S19206753602005091400000) or «Air Delivery Improper - Auxiliary (W/Sunroof)»(ref-190277-S33699666292005091400000)
16. «Air Recirculation Malfunction»(ref-190277-S18694056302005091400000)
17. «LEAK TESTING»(ref-156625-S14709773682003072300000) in Heating, Ventilation and Air Conditioning
18. TEST L: DEFROSTING INSUFFICIENT in Heating, Ventilation and Air Conditioning