• 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.

When the A/C switch is pressed, an A/C request message is sent to the engine control module (ECM) via serial data. If specific criteria is met, 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.

• Engine is running.
• The HVAC control module is ON.
• The A/C switch is active.

The ECM detects a short to ground or an open at the A/C compressor clutch relay control circuit.

The ECM detects a short to voltage at the A/C compressor clutch relay control circuit.

The A/C compressor is inoperative or always active.

The A/C compressor is inoperative.

The condition for setting the DTC is no longer present.

HVAC Schematics

Master Electrical Component List

Manual HVAC Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Control Module References for scan tool information

1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay, ignition ON.
2. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF, remove the test lamp.
2. 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
1. Ignition OFF, remove the test lamp.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Disconnect the harness connector at the Q2 A/C Compressor Clutch.
4. Test for infinite resistance between the control circuit terminal 2 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.
• If the test lamp illuminates
3. Ignition ON.
4. Verify a test lamp illuminates between the ignition circuit terminal 1 and ground.
• If the test lamp does not illuminate

  Refer to Power Mode Mismatch.

• If the test lamp illuminates
5. Connect a test lamp between the ignition circuit terminal 1 and the control circuit terminal 2.
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
1. Ignition OFF, remove the test lamp and 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 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
1. Ignition OFF, remove the test lamp and 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
7. Verify a test lamp does not illuminate between the control circuit terminal 5 and ground.
• If the test lamp illuminates

  Repair the short to voltage on the circuit.

• 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.
• If 10 Ω or greater
1. Ignition OFF.
2. 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.
• 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 3 and the control circuit terminal 5.
12. Verify the Q2 A/C Compressor Clutch is engaged.
• If the Q2 A/C Compressor Clutch does not engage
1. Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch.
2. 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.
• If the Q2 A/C Compressor Clutch is engaged
13. Test or replace the KR29 A/C Compressor Clutch Relay.

1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 60–180 Ω between terminals 1 and 2.
• If not between 60–180 Ω

  Replace the KR29 A/C Compressor Clutch Relay.

• If between 60–180 Ω
3. Test for infinite resistance between the terminals listed below:
• 3 and 1
• 3 and 2
• 3 and 5
• 1 and 5
• If less than infinite resistance

  Replace the KR29 A/C Compressor Clutch Relay.

• If infinite resistance
4. Install a 15 A fused jumper wire between terminal 1 and 12 V. Install a jumper wire between terminal 2 and ground.
5. Test for less than 2 Ω between terminals 3 and 5.
• If 2 Ω or greater

  Replace the KR29 A/C Compressor Clutch Relay.

• If less than 2 Ω
6. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

• HVAC Component Replacement Reference
• Control Module References for control module replacement, programming and setup