Buick Regal: 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 (A/C) Compressor Clutch Relay Control Circuit
DTC P0646
Air Conditioning (A/C) Compressor Clutch Relay Control Circuit Low Voltage
DTC P0647
Air Conditioning (A/C) Compressor Clutch Relay Control Circuit High Voltage
Diagnostic Fault Information
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 serial data. The ECM then grounds the A/C 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 HVAC control module is ON.
- The A/C switch is active.
Conditions for Setting the DTC
P0645 or P0646
The ECM detects a short to ground or an open at the A/C compressor clutch
relay control circuit.
P0647
The ECM detects a short to voltage at the A/C compressor clutch relay control
circuit.
Action Taken When the DTC Sets
P0645 or P0646
The A/C compressor is inoperative or always active. The A/C compressor
solenoid is commanded to 0%
displacement. This causes warm air from the ducts, even with unwanted clutch
engagement.
P0647
The A/C compressor is inoperative.
Conditions for Clearing the DTC
The condition for setting the DTC is no longer present.
Reference Information
Schematic Reference
HVAC Wiring Schematics
Connector End View Reference
Component Connector End View Index
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
1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay, ignition
ON.
2. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
- If the test lamp does not illuminate and the circuit fuse is good
- Ignition OFF, remove the test lamp.
- Test for less than 2 Ω in the B+ circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, verify the fuse is not open and there is voltage
at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
- Ignition OFF, remove the test lamp.
- Test for infinite resistance between the B+ circuit and ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- Go to next step: If infinite resistance
- Disconnect the harness connector at the Q2 A/C Compressor Clutch.
- Test for infinite resistance between the control circuit terminal 87 and
ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance, test or replace the Q2 A/C Compressor
Clutch.
- Go to next step: If the test lamp illuminates
3. Ignition ON.
4. 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.
- Go to next step: If the test lamp illuminates
5. Connect a test lamp between the ignition circuit terminal 86 and the
control circuit terminal 85.
6. Verify the test lamp turns ON and OFF when commanding the ECM A/C Compressor
Clutch
Relay On and Off with a scan tool.
- If the test lamp is always OFF
- Ignition OFF, remove the test lamp and disconnect the harness connector at
the K20 EngineControl Module, ignition ON.
- 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.
- Go to next step: If less than 1 V
- Ignition OFF.
- Test for less than 2 Ω in the control circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K20 Engine Control Module.
- If the test lamp is always ON
- Ignition OFF, remove the test lamp and disconnect the harness connector at
the K20 EngineControl Module.
- 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.
- Go to next step: If the test lamp turns ON and OFF
7. Verify a test lamp does not illuminate between the control circuit
terminal 87 and ground.
- If the test lamp illuminates
Repair the short to voltage on the circuit.
- Go to next step: If the test lamp does not illuminate
8. Ignition OFF and all vehicle systems OFF, disconnect the harness connector
at the Q2 A/C
Compressor Clutch. It may take up to 2 min for all vehicle systems to power
down.
9. Test for less than 10 Ω between the ground circuit terminal 1 and ground.
- Ignition OFF.
- Test for less than 2 Ω in the ground circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, repair the open/high resistance in the ground
connection.
- Go to next step: If less than 10 Ω
10. Connect the harness connector at the Q2 A/C Compressor Clutch.
11. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit
terminal 30 and the control
circuit terminal 87.
12. Verify the Q2 A/C Compressor Clutch is engaged.
- If the Q2 A/C Compressor Clutch does not engaged.
- Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor
Clutch.
- Test for less than 2 Ω in the control circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, test or replace the Q2 A/C Compressor Clutch.
- Go to next step: If the Q2 A/C Compressor Clutch is engaged
13. Test or replace the KR29 A/C Compressor Clutch Relay.
Component Testing
1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 60 - 180 Ω between terminals 85 and 86.
- If not between 60 - 180 Ω
Replace the KR29 A/C Compressor Clutch Relay.
- Go to next step: If between 60 - 180 Ω
3. 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 A/C Compressor Clutch Relay.
- Go to next step: If infinite resistance
4. Install a 15 A fused jumper wire between terminal 86 and 12 V. Install a
jumper wire between
terminal 85 and ground.
5. Test for less than 2 Ω between terminals 30 and 87.
Replace the KR29 A/C Compressor Clutch Relay.
- Go to next step: If less than 2 Ω
6. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
- HVAC Component Replacement Reference
- Control Module References for engine control module replacement,
programming and setup
READ NEXT:
NOTE: The following steps must be completed before using the symptom
tables:
1. Perform the Diagnostic System Check - Vehicle before using the HVAC System
Malfunction
procedure in order to verify th
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.
Diag
Afterblow is a feature that dries the evaporator core by operating the blower
motor after the engine is
turned off. This aids in reducing microbial growth that can create undesirable
odors.
The veh
SEE MORE:
SPECIFICATIONS
APPROXIMATE FLUID CAPACITIES
FLUID AND LUBRICANT RECOMMENDATIONS
MAINTENANCE ITEMS
MAINTENANCE REPLACEMENT PARTS
Replacement parts identified below by name, part number, or specification can
be obtained from your
dealer.
MAINTENANCE
MAINTENANCE SCHEDULE
The Maintenance Schedule
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
D