Diagnostic Instructions

DTC Descriptors

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

DTC P0646: Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage

DTC P0647: Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
A/C Compressor Clutch Relay Control	P0645 P0646	P0645 P0646 P0647	P0645	--
A/C Relay coil side supply voltage circuit	1	1	--	--
A/C Relay coil side ground circuit	--	1	--	--
Ignition 1 circuit	1	1	--	--
B+ circuit	1	1	--	--
1. Circuit Inoperative

Circuit/System Description

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, a DTC will set.

Conditions for Running the DTC

Conditions for Setting the DTCs

The ECM detects an open on the control circuit of the A/C compressor clutch relay when commanded off with the engine in crank or run status.

Action Taken When the DTC Sets

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.

Conditions for Clearing the DTC

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for Scan Tool Reference

Circuit/System Verification

1. Install a scan tool.
2. Ignition ON with the engine OFF, command the A/C Relay ON and OFF in the ECM Special Functions scan tool data list.
3. Feel/listen for the A/C relay to click. Observe the scan tool A/C Relay Circuit Status function or A/C relay solenoid turns on and off clicks.

Circuit/System Testing

1. Ignition OFF, disconnect the A/C Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the controlled output circuit, and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay ignition circuit and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test or replace the A/C Compressor Clutch Relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit, and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay ignition output circuit for a short to ground.

⇒	If the test lamp does not illuminate, test the relay switch ignition circuit for an open/high resistance.

5. Disconnect the harness connector at the A/C Compressor Clutch Coil.
6. Test for less than 1 ohm between the A/C Compressor Clutch Coil terminal B ground circuit terminal and ground.

⇒	If greater than 1 ohm, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the A/C Compressor Clutch Coil.
8. Connect a 3A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the A/C Clutch Relay is activated.

⇒	If the A/C Compressor Clutch Relay does not activate, test the relay controlled circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C Compressor Clutch Relay.

9. Connect a test lamp between the relay coil ignition circuit, and the relay coil control circuit.
10. Command the A/C Relay output function ON and OFF with a scan tool. 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.

⇒	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.

11. If all circuits test normal, test or replace the A/C Compressor Clutch Relay.

Component Testing

Relay Testing

1. Ignition OFF, disconnect the A/C Compressor Clutch Relay.
2. Test for 137 ohms across the relay coil B+ and relay coil output controlled circuits.

⇒	If the resistance is not close to the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

⇒	Relay switch B+ and the relay switch controlled output

⇒	If less than infinite resistance, replace the relay.

4. Install a 20A fused jumper wire between relay coil B+ and 12 volts. Install a jumper wire between relay coil control and ground. Measure for less than 2 ohms between the relay switch B+circuit and relay switch controlled output circuit.

⇒	If greater than 2 ohms, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.