DTC P0645, P0646, or P0647

Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptors DTC P0645 Air Conditioning Compressor Clutch Relay Control Circuit DTC P0646 Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage DTC P0647 Air Conditioning Compressor Clutch Relay Control Circuit High Voltage Diagnostic Fault Information

Circuit Number	Circuit Function	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performan
59	Control	1	1	2	-
459	Control	P0646	P0645	P0647	—
6550	Ground	-	1	-	-
1. Air Conditioning Compressor Clutch Inoperative 2. Air Conditioning Compressor Clutch Always On

Circuit/System Description When compressor operation is needed for the HVAC system, the body control module sends a request message to the engine control module (ECM) via serial data. The ECM then grounds the air conditioning compressor clutch relay coil control circuit, closing the relay contacts. The closed relay contacts provide voltage to the compressor clutch causing it to engage. Conditions for Running the DTC Engine is running. The compressor request is active. Conditions for Setting the DTC P0645 Circuit 459 has an open or high resistance P0646 Circuit 459 is shorted to ground P0647 Circuit 459 is shorted to voltage Action Taken When the DTC Sets P0645 or P0646 The air conditioning compressor is inoperative. DTC Type C P0647 The air conditioning compressor clutch is always ON. The air conditioning compressor solenoid is commanded to 0% displacement. This causes warm air from the ducts, even with unwanted clutch engagement. DTC Type C Conditions for Clearing the DTC DTC Type C Reference Information Schematic Reference HVAC Schematics Connector End View Reference Master Electrical Component List Description and Operation Automatic HVAC Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Circuit/System Testing

Ignition OFF, disconnect the KR29 Air Conditioning Compressor Relay, ignition ON.
Verify a test lamp illuminates between the B+ circuit terminal 30 and ground. ⇒ If the test lamp does not illuminate Replace the X50A Fuse Block – Underhood ⇓ If the test lamp illuminates
Ignition ON.
Verify a test lamp illuminates between the ignition circuit terminal 86 and ground. ⇒ If the test lamp does not illuminate Refer to Power Mode Mismatch. ⇓ If the test lamp illuminates
Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
Verify the test lamp turns ON and OFF when commanding the ECM Air Conditioning Compressor Clutch Relay On and Off with a scan tool. ⇒ If the test lamp is always OFF 6.1. Test circuit 459 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 6.2. Test circuit 459 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 6.3. Replace the K20 Engine Control Module ⇒ If the test lamp is always ON 6.1. Test circuit 459 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 6.2. Replace the K20 Engine Control Module ⇓ If the test lamp turns ON and OFF
Ignition OFF and all vehicle systems OFF, disconnect the connector at the Q2 Air Conditioning Clutch. It may take up to 2 min for all vehicle systems to power down.
Test for less than 10 Ω between the ground circuit terminal 1 and ground. ⇒ If 10 Ω or greater Repair the open/high resistance on circuit 6550 or the ground connection. ⇓ If less than 10 Ω
Connect the KR29 Air Conditioning Compressor Relay.
Connect a test lamp between the Q2 Air Conditioning Clutch control circuit terminal 2 and ground circuit terminal 1, ignition ON.
Verify the test lamp turns ON and OFF when commanding the ECM Air Conditioning Compressor Clutch Relay On and Off with a scan tool. ⇒ If the test lamp is always OFF and the circuit fuse is good 11.1. Test circuit 59 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 11.2. Replace the KR29 Air Conditioning Compressor Clutch relay ⇒ If the test lamp is always OFF and the circuit fuse is open 11.1. Test circuit 59 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 11.2. Replace the Q2 Air Conditioning Clutch ⇒ If the test lamp is always ON 11.1. Test circuit 59 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 11.2. Replace the KR29 Air Conditioning Compressor Clutch relay ⇓ If the test lamp turns ON and OFF
Replace the Q2 Air Conditioning Clutch Component Testing
Ignition OFF, disconnect the KR29 Air Conditioning Compressor Relay.
Test for 60–180 Ω between terminals 85 and 86. ⇒ If not between 60–180 Ω Replace the KR29 Air Conditioning Compressor Relay. ⇓ If between 60–180 Ω
Test for infinite resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 ⇒ If less than infinite resistance Replace the KR29 Air Conditioning Compressor Relay. ⇓ If infinite resistance
Install a 15 A fused jumper wire between terminal 86 and 12 V. Install a jumper wire between terminal 85 and ground.
Test for less than 2 Ω between terminals 30 and 87. ⇒ If 2 Ω or greater Replace the KR29 Air Conditioning Compressor Relay. ⇓ If less than 2 Ω
All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. HVAC Component Replacement Reference Control Module References for control module replacement, programming and setup