HVAC - Automatic
DTC P0645
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/System Description
When the A/C switch is pressed, the HVAC control module sends an A/C request message to the engine control module (ECM) via CAN-Bus. The ECM then grounds the A/C compressor clutch relay control circuit, closing the A/C compressor clutch relay contacts. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch and A/C compressor clutch is activated.
Reference Information
Schematic Reference
HVAC Schematics HVAC - Automatic
Connector End View Reference
Component Connector End Views Outside Rearview Mirror - Driver
Description and Operation
Automatic HVAC Description and Operation HVAC - Automatic
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Testing
1. Ignition OFF, disconnect the X3 harness connector at X50A fuse block-underhood.
2. Remove the control circuit terminal 34 using terminal release tool J-44020-4, connect the X3 harness connector to the X50 fuse block underhood.
3. Connect a test lamp between the control circuit terminal 34 and B+, engine running.
4. Verify the test lamp turns ON and OFF when commanding the Q2 A/C compressor clutch ON and OFF with a scan tool.
• If the test lamp is always OFF
1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Ignition OFF
4. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K20 ECM.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the K20 Engine Control Module.
• If the test lamp turns ON and OFF
5. Ignition OFF and all vehicle systems OFF, connect the harness connector at the X50A fuse block-underhood, disconnect the harness connector at the Q2 A/C compressor clutch. It may take up to 2 minutes for all vehicle systems to power down.
6. Test for less than 10 ohms between the Q2 A/C compressor clutch ground terminal 1 and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
7. Connect a test lamp between the control circuit terminal 2 and ground.
8. Verify the test lamp turns ON and OFF when commanding the Q2 A/C compressor clutch ON and OFF with a scan tool.
• If the test lamp is always OFF and the circuit fuse is good
1. Ignition OFF, disconnect the X1 harness connector at the X50A fuse block-underhood.
2. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the X50A fuse block-underhood.
• If the test lamp is always OFF and the circuit fuse is open
1. Ignition OFF
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the Q2 A/C compressor clutch.
• If the test lamp is always ON
1. Ignition OFF, disconnect the X1 harness connector at the X50A fuse block-underhood, Ignition ON.
2. Test for less then 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the X50A fuse block-underhood.
• If the test lamp turns ON and OFF
9. Replace the Q2 A/C compressor clutch.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* HVAC Component Replacement Reference Removal and Replacement
* Control Module References Control Module References for HVAC control module programming and setup