HVAC Systems - Automatic: Diagnosis Chevrolet Silverado 3500

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

PCM Scan Tool Output Controls

Scan Tool Data List

BCM Scan Tool Data List

HVAC Control Module 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 has an AUTO mode algorithm that is designed to detect a failure with the blower system or a failure with the A/C system. The HVAC control module, when in AUTO mode, requests the engine ON when continuous operation of the A/C compressor (not interrupted by the engine shutting off during stops) is required to cool the cabin in warm or hot weather. The failure detection algorithm monitors duct temperatures while the engine is requested ON under such conditions. If the algorithm does not see duct temperatures become cooler than 120 counts within 30 minutes of requesting the engine on for A/C operation the B013A will set and the HVAC control module will not request engine ON for A/C in warm or hot weather until the B013A is cleared.

The failure detection algorithm will activate if the following conditions are present

1. The HVAC module is in AUTO mode.
2. The Outside air temperature sensor is in normal operating range.
3. The Inside air temperature sensor is in normal operating range.
4. The Sunload sensor is in normal operating range.
5. The Duct temperature sensors are in normal operating range and are reading warmer than 120 counts (warmer temperatures correspond to lower A/D count values).
6. A temperature setting that requires A/C operation under the current ambient conditions must be selected on the HVAC module.

Algorithm is a word that describes one of the many functions of the software inside the module. The algorithm looks at specific information that the HVAC module receives and based off that information the algorithm outputs specific functions. There is no single circuit or component that performs these functions; it is a combination of inputs, outputs and module function.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B013A A/C System Performance

Conditions for Running the DTC

1. The ignition is turned ON.
2. The HVAC control module is in AUTO mode.
3. The HVAC control module must be requesting engine ON for A/C.

Conditions for Setting the DTC

The HVAC control module is requesting engine ON for A/C and detects duct temperatures warmer than 120 counts for more than 30 minutes.

Action Taken When the DTC Sets

1. The HVAC control module will no longer request the engine on for A/C.
2. No other fail soft actions are taken, and no telltales or other indications are given to indicate a system fault.
3. The DTC will be set until cleared with a scan tool.

Conditions for Clearing the DTC

The DTC can be cleared with a scan tool.

Diagnostic Aids

If the vehicle is under extreme load-such as extended idles at hot ambient or an intermittent failure with the blower system or A/C system This may cause the DTC to set if the failure has been present for more than 30 minutes on one ignition cycle.

The following DTCs are for the ambient air temperature sensor and for the inside air temperature sensor assembly

1. B0159 is for the ambient air temperature sensor.
2. B0164 is for the inside air temperature sensor assembly.

The ambient air temperature sensor allows the HVAC control module to monitor the temperature of the air surrounding the front of the vehicle. The inside air temperature sensor assembly allows the HVAC control module to monitor the temperature of the air inside the passenger compartment. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuits. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. The HVAC control module also uses the ambient air temperature input to calculate the value of the ambient air temperature display. When the air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the air temperatures are hot, the resistances of the sensors are low and the voltage signals are low.

1. Battery voltage to the HVAC control module is greater than 8.7 V and less than 16.5 V.
2. The ignition is turned ON.

The HVAC control module determines that the voltage applied to the input for the air temperature sensor is less than 0.09 V or greater than 4.9 V.

1. The HVAC control module uses a default value of 10°C (50°F) for the ambient air temperature display. The scan tool also displays 10°C (50°F) as the value for the Outside Air Temp. Raw parameter.
2. The HVAC control module use a default value of 25°C (77°F) for the Inside Air Temp. parameter.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

The following DTCs are for the air temperature sensors located in the discharge air ducts

1. B0174 is for the upper left air temperature sensor.
2. B0179 is for the lower left air temperature sensor.
3. B0510 is for the upper right air temperature sensor.
4. B0515 is for the lower right air temperature sensor.

Air temperature sensors allow the HVAC control module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 V is approximately equal to 51 counts.

1. Battery voltage is within 8.7-16.5 V.
2. The ignition is ON.

The HVAC control module determines that the value of the air temperature parameter is less than 5 counts or greater than 250 counts.

The HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.

1. The DTC will become history if the HVAC control module no longer detects a fault.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

The following DTCs are for the left and right sunload sensors.

1. B0183 is for the left sunload sensor.
2. B0188 is for the right sunload sensor.

The left and right sunload sensors provide the HVAC control module with inputs as to the amount heat load the sun is placing on the interior of the vehicle. The sunload sensors are photodiodes that are sensitive to light intensity. The Body Control Module (BCM) applies 5 volts to internal input resistors that are connected to the left and right signal circuits of the sunload sensor assembly. The BCM provides ground to the sensors through the low reference circuit. The BCM monitors the voltage drops across the sunload sensors and converts the voltage values to count values where 1 V is approximately equal to 51 counts. As the light intensity increases, the sunload sensors allow more current to travel through the circuits and the signal voltages decrease. As the light intensity decreases, the sunload sensors allow less current to travel through the circuits and the signal voltages increase. The BCM transmits the data to the HVAC control module over the class 2 serial data circuit.

The ignition is ON.

The BCM determines that the value of the sunload sensor signal is less than 5 counts or greater than 250 counts.

The action taken will be for the BCM to revert to a calibrated default value.

1. The DTC will become history if the BCM no longer detects a failure.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

The following DTCs are for the HVAC door actuators

1. B0229 is for the recirculation actuator.
2. B0414 is for the left air temperature actuator.
3. B0424 is for the right air temperature actuator.
4. B3770 is for the mode actuator.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The module supplies a 5-volt source voltage to the potentiometer on the 5-volt reference circuit. The module supplies ground to the potentiometer through the low reference circuit. 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 module converts the voltage value to a count value where 1-volt is approximately equal to 51 counts.

The HVAC control module calibrates the travel range of the HVAC door actuators when it is initially powered by the battery positive voltage circuit. During calibration, the module commands the actuators in each direction until door travel is stopped. The module stores the minimum door positions and the maximum door positions of each actuator into memory. The total travel range is calculated by subtracting the minimum door position from the maximum door position. The door actuators can be calibrated again with a scan tool.

1. Battery voltage is 8.7-16.5 volts.
2. The ignition is ON.

The DTC sets when one of the following conditions are present

1. The actual door position value for the actuator is less than 5 counts.
2. The actual door position value for the actuator is greater than 250 counts.
3. The actuator fails calibration because the calculated travel range value is too great or too small.

1. If the DTC sets because the actual door position value is out of range, the HVAC control module will command the actuator to a default position.
2. If the DTC sets because the actuator failed a calibration, the HVAC control module will attempt to calibrate the motor in the next transition from OFF to RUN mode.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

1. If the condition is not present refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. If the DTC sets following a calibration of the door actuator, inspect the door and the actuator for the following conditions: A misaligned actuator Broken linkages or binding linkages A broken door or a binding door An obstruction that prevents the door from operating within the full range of motion Missing seals to the door Poor connections at the harness connector of the door actuator
3. If a signal circuit of an actuator is short to ground and the resistance across the internal potentiometer is low, then this condition could cause a multiple DTC concern.

The following DTCs are for the HVAC door actuators

1. B0263 is for the mode actuator.
2. B0268 is for the recirculation actuator.
3. B0408 is for the left air temperature actuator.
4. B0418 is for the right air temperature actuator.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The logic circuit inside the actuators receives control signals from the HVAC control module and controls the internal stepper motor. When a door positional change is required, the HVAC control module calculates a commanded door position. The module compares the commanded door position to the actual door position and determines the needed direction of motor rotation. The module applies a signal voltage to the door control circuit that is an input to the internal logic circuit of the door actuator. A 5-volt signal increases the door position. A 0-volt signal decreases the door position. When the commanded door position is equal to the actual door position, the HVAC control module sends a 2.5-volt signal to the door actuator and motor rotation stops. The ignition 3-voltage circuit provides source voltage to the logic circuit. The module provides ground to the actuator logic circuit through the low reference circuit.

1. Source voltage is 8.7-16.5 volts.
2. The ignition is ON.
3. The HVAC control module commands the actuator to move.

The actual door position is not near the commanded door position.

The HVAC control module does not command the actuator to move for the remainder of the ignition cycle.

1. The DTC becomes history during the next ignition cycle in which the HVAC control module no longer detects a stall condition.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

1. If the condition is not present refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. Inspect the appropriate door and door actuator for the following conditions: A misaligned door actuator Binding linkages A binding door An obstruction that prevents the door actuator from operating within the full range of motion

The HVAC control module monitors the upper left and upper right duct temperature sensors when the mode switch is in the VENT or BI-LEVEL positions. The HVAC control module monitors the lower left and lower right duct temperature sensors when the mode switch is in the DEFOG, FLOOR or FRONT DEFROST positions. The duct sensors are used to measure the temperature of the air exiting the ducts to help maintain a consistent cabin air temperature. These duct sensor inputs provide the HVAC control module a way to determine if the engine needs to be started to maintain a specific air temperature. If an upper duct sensor circuit failure is detected the HVAC module will not request an engine start to help cool the cabin. A lower duct sensor circuit failure will not prevent the engine from starting.

The ignition has been in the OFF position for 4 hours.

1. After a 4 hour ignition OFF the difference of lower air temperature sensors count value is more than 40 counts.
2. After engine has started, within the first 20 minutes, and the conditions are present for the HVAC control module to place the air temperature doors to the maximum heat position and the air temperature sensor count value does not change at least 50 counts.
3. If the previous condition has passed a second 20 minute timer is started and conditions are present for maximum heat and the air temperature sensors are more than 40 counts apart any time during this second 20 minute timer.

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The driver information center, if equipped, may display a message.
4. The HVAC control module will not request an engine restart while in continuous mode.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.

1. If the condition is intermittent, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. An air temperature sensor not installed properly in the HVAC duct may cause this DTC.
3. DTC B0174, B0179, B0510 and B0515 must be repaired before this diagnostic is completed or misdiagnosis will occur.

The HVAC control module monitors the upper left and upper right duct temperature sensors when the mode switch is in the VENT or BI-LEVEL positions. The HVAC control module monitors the lower left and lower right duct temperature sensors when the mode switch is in the DEFOG, FLOOR or FRONT DEFROST positions. The duct sensors are used to measure the temperature of the air exiting the ducts to help maintain a consistent cabin air temperature. These duct sensor inputs provide the HVAC control module a way to determine if the engine needs to be started to maintain a specific air temperature. If an upper duct sensor circuit failure is detected the HVAC module will not request an engine start to help cool the cabin. A lower duct sensor circuit failure will not prevent the engine from starting.

The ignition has been in the OFF position for 4 hours.

1. After a 4 hour ignition OFF the difference of lower air temperature sensors count value is more than 40 counts.
2. After engine has started, within the first 20 minutes, and the conditions are present for the HVAC control module to place the air temperature doors to the maximum heat position and the air temperature sensor count value does not change at least 50 counts.
3. If the previous condition has passed a second 20 minute timer is started and conditions are present for maximum heat and the air temperature sensors are more than 40 counts apart any time during this second 20 minute timer.

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The driver information center, if equipped, may display a message.
4. The HVAC control module will not request an engine restart while in continuous mode.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.

1. If the condition is intermittent, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. An air temperature sensor not installed properly in the HVAC duct may cause this DTC.
3. DTC B0174, B0179, B0510 and B0515 must be repaired before this diagnostic is completed or misdiagnosis will occur.

The ignition 3 voltage circuit is a discrete input to the HVAC control module. The HVAC control modules uses the input to determine that the ignition switch is in the RUN position. When the ignition switch is in the RUN position, ignition voltage is applied to the input.

1. Source voltage is 8.7-16.5 volts.
2. The HVAC control module receives a RUN power mode message from the BCM over the class 2 serial data circuit.

The HVAC control module does not detect ignition voltage on the ignition 3 voltage input.

The HVAC control module will continue to operate using the class 2 power mode messaging.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

DTC B1375

The powertrain control module (PCM) or engine control module (ECM) monitors the high side refrigerant pressure via a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is too high the PCM will not allow the A/C compressor clutch to engage.

The PCM/ECM detects an A/C request.

1. The A/C refrigerant pressure sensor signal is less than 0.1 volts for 5 seconds.
2. The A/C refrigerant pressure sensor signal is greater than 4.9 volts for 5 seconds.

The malfunction indicator lamp (MIL) will not illuminate.

1. The DTC will become history if the PCM/ECM no longer detects a failure.
2. The history DTC will clear after 40 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

The engine control module (ECM) monitors the high side refrigerant pressure via a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is too high the PCM will not allow the A/C compressor clutch to engage.

The ECM detects an A/C request.

1. The A/C refrigerant pressure sensor signal is less than 0.1 volts for 5 seconds.
2. The A/C refrigerant pressure sensor signal is greater than 4.9 volts for 5 seconds.

The malfunction indicator lamp (MIL) will not illuminate.

1. The DTC will become history if the ECM no longer detects a failure.
2. The history DTC will clear after 40 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(ref-184114-S31353837752005082200000) in Wiring Systems.
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-184159-S36861041392005082200000) .
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-184159-S14539779832005082200000)
2. «HVAC Compressor Clutch Does Not Disengage»(ref-184159-S33973563312005082200000)
3. «Blower Motor Always On»(ref-184159-S31965295412005082200000)
4. «Blower Motor Inoperative»(ref-184159-S29510254882005082200000)
5. «Blower Motor Malfunction»(ref-184159-S17418430722005082200000)
6. «Too Hot in Vehicle»(ref-184159-S28403092992005082200000)
7. «Too Cold in Vehicle»(ref-184159-S42403571342005082200000)
8. «Air Delivery Improper»(ref-184159-S39565876962005082200000)
9. «Air Recirculation Malfunction»(ref-184159-S07256571562005082200000)
10. «Leak Testing»(ref-184172-S21517647062005082200000) in Heating, Ventilation and Air Conditioning
11. «Noise Diagnosis - Blower Motor»(ref-184172-S26092968362005082200000) in Heating, Ventilation and Air Conditioning
12. «Noise Diagnosis - Air Conditioning (A/C) System»(ref-184172-S02170366542005082200000) in Heating, Ventilation and Air Conditioning
13. «Noise Diagnosis - HVAC Module»(ref-184172-S11186720132005082200000) in Heating, Ventilation and Air Conditioning
14. «Odor Diagnosis»(ref-184172-S31364715042005082200000) in Heating, Ventilation and Air Conditioning

The air conditioning (A/C) compressor clutch will not engage under the following conditions

1. The A/C high side line pressure is over 2957 kPa (429 psi).
2. The A/C low side line pressure is under 138-172 kPa (20-25 psi).
3. Throttle angle is at 100 percent.
4. Engine speed is more than 5500 RPM.
5. Engine coolant temperature (ECT) is more than 121°C (250°F).
6. Ambient air temperature is less than 5°C (40°F).
7. Engine is idling at a low unstable RPM

Compressor clutch engagement cannot be used to determine status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the powertrain control module (PCM) that control A/C compressor clutch engagement.

To accurately determine what pressure the A/C low pressure switch opens and closes at use Kent Moore GE-47742 which will allow the technician to measure the switch point pressure at the switch.

Using a scan tool, monitor the "low pressure switch" status while monitoring the "low side" pressure at the switch to determine the switch points of the low pressure switch.

The low pressure switch "connector seal" must be removed before plugging it into the switch for testing. The "plunger effect" of plugging the connector with seal into the switch induces a pressure on the back side of the switch, this pressure will skew the opening/closing characteristics of the switch 5-10 psi until the pressure bleeds off. The time required for the connection induced pressure to bleed off can take 20 minutes or longer.

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. The air temperature actuators can be calibrated. Refer to «Re-Calibrating Actuators»(ref-184158-S21524317232005082200000) .

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. The air temperature actuators can be calibrated. Refer to «Re-Calibrating Actuators»(ref-184158-S21524317232005082200000) .

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-184114-S28299220792005082200000) in Wiring Systems.
2. Inspect the air delivery system for the following conditions: A dirty HVAC air filter, if applicable An obstruction to the airflow Air leaks Misaligned air ducts Broken or binding linkages or doors

Air Delivery Improper