HVAC System - Automatic: Diagnosis Chevrolet Silverado 2500 HD

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

PCM Scan Tool Output Controls

Rear HVAC/RSA Module

Scan Tool Data List

BCM Scan Tool Data List

HVAC Control Module Scan Tool Data List

PCM Scan Tool Data List

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

Diagnostic Fault Information

DTC B0158, B0163, B0173, B0178, B0509, or B0514

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the appropriate ground circuit terminal and ground. Duct temperature sensor ground circuit terminal A Ambient temperature sensor ground circuit terminal B Inside air temperature sensor ground circuit terminal C If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the appropriate scan tool temperature sensor parameter is greater than 250 counts. If less than the specified range, test the appropriate signal circuit terminal for a short to ground. If the circuit tests normal, replace the HVAC control module. Duct temperature sensor signal circuit terminal B Ambient temperature sensor signal circuit terminal A Inside air temperature sensor signal circuit terminal B
4. Install a 3A fused jumper wire between the appropriate signal circuit terminal and ground. Verify the appropriate scan tool temperature sensor parameter is less than 5 counts. Duct temperature sensor signal circuit terminal B Ambient temperature sensor signal circuit terminal A Inside air temperature sensor signal circuit terminal B If greater than the specified range, 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. If all circuits test normal, test or replace the appropriate temperature sensor.

Circuit Description

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 volt 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 GM LAN data circuit.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC B0183 05 Solar Load Sensor 1 Circuit Short to Short to Battery or Open
2. DTC B0183 02 Solar Load Sensor 1 Circuit Short to Ground
3. DTC B0188 05 Solar Load Sensor 2 Circuit Short to Short to Battery or Open
4. DTC B0188 02 Solar Load Sensor 2 Circuit Short to Ground

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

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

Conditions for Clearing the DTC

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC B0228, B0413, B0423, or B3779

1. Ignition OFF, disconnect the harness connector at the applicable actuator.
2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal 7 and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 10 and ground. If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module. If less then specified range, 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.
4. Verify the applicable scan tool parameter is less than 7 counts. If greater than the specified range, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the HVAC control module.
5. Install a 3A fused jumper wire between the signal circuit terminal 9 and the low reference circuit terminal 7. Verify the applicable scan tool parameter is greater than 250 counts. If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Verify that a test lamp illuminates between the ignition circuit terminal 5 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
7. Test for 2.5 volts between the control circuit terminal 6 and ground. If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module. If less then specified range, 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.
8. Install a DMM between the control circuit terminal 6 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 5 volts in the other direction and return to 2.5 volts in the at rest state. If the voltage does not change as specified, replace the HVAC control module.
9. If all circuits test normal, test or replace the applicable actuator.

The engine control module (ECM) monitors the high side refrigerant pressure through an 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 high, the ECM commands the cooling fans on. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage. The ECM sends the A/C pressure data to the body control module (BCM) over the GM LAN serial data circuit. This keeps the high side pressure in a normal operating range. This will prevent the A/C compressor clutch from disengaging under normal operating conditions. The BCM will not request A/C compressor clutch engagement if the A/C pressure is too high.

This diagnostic procedure supports the following DTCs

1. DTC P0532 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage
2. DTC P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage

The engine is running.

1. A/C pressure of less than 0.3 volts or more than 4.92 volts.
2. The condition must be present for more than 5 seconds.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM will store the conditions present when the DTC set as Fail Records data only.

1. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

Test the following conditions

1. Visually inspect the sensor for contamination or damage.
2. Inspect for the following that may affect the sensors accuracy: A malfunction within the refrigerant system causing low pressure Visually inspect the A/C components and lines for damage.
3. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-278019-S21810776732008012100000) .

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the A/C clutch relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The ECM will monitor the control circuit for the following

1. A short to ground
2. A short to voltage
3. An open circuit
4. An open relay coil
5. An internally shorted or excessively low resistance relay coil

When the ECM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.

This diagnostic procedure supports the following DTC

DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit

1. The ignition voltage is between 9-18 volts.
2. The engine speed is more than 80 RPM.
3. The ECM driver transitions from ON to OFF or from OFF to ON.

The ECM detects an open on the control circuit of the A/C compressor clutch relay.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

1. A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The DTC can be cleared by using a scan tool.

If DTC P0645 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC P0646 or P0647

An A/C request is received from the HVAC module.

A short to voltage, short to ground, or open/high resistance is seen on the A/C compressor clutch relay control circuit.

DTC P0646 and DTC P0647 are Type C DTCs

DTC P0646 and DTC P0647 are Type C DTCs

1. Ignition OFF, disconnect the A/C relay.
2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
3. Connect a test lamp between the relay coil B+ circuit terminal and the A/C compressor clutch relay control circuit terminal.
4. Engine running, command the A/C relay ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM/PCM. If the test lamp is always OFF< test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM/PCM.
5. If all circuits test normal, test or replace the A/C relay.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(ref-278019-S10639375482008012100000) .
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. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(ref-277999-S14918532022008012100000) .
5. 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
6. 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-277999-S38180221362008012100000)
2. «HVAC Compressor Clutch Does Not Disengage»(ref-277999-S07499699702008012100000)
3. «Blower Motor Always On»(ref-277999-S18031965182008012100000)
4. «Blower Motor Inoperative»(ref-277999-S39421661662008012100000)
5. «Blower Motor Malfunction»(ref-277999-S05635398242008012100000)
6. «Too Hot in Vehicle»(ref-277999-S14818259162008012100000)
7. «Too Cold in Vehicle»(ref-277999-S15127569772008012100000)
8. «Air Delivery Improper»(ref-277999-S03727658402008012100000)
9. «Air Recirculation Malfunction»(ref-277999-S12078611552008012100000)
10. «Leak Testing»(ref-277995-S05500064362008012100000) .
11. «Noise Diagnosis - Blower Motor»(ref-277995-S27506954212008012100000) .
12. «Noise Diagnosis - Air Conditioning (A/C) System»(ref-277995-S36327774822008012100000) .
13. «Noise Diagnosis - HVAC Module»(ref-277995-S16367301652008012100000) .
14. «Odor Diagnosis»(ref-277995-S26739813832008012100000) .

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 5,500 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 engine control module (ECM) 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-278019-S21810776732008012100000) .
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