P0645
DTC P0645
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0645
- Air Conditioning (A/C) Clutch Relay Control Circuit
Diagnostic Fault Information
Circuit 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 volt. 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, this DTC will set.
The ECM will monitor the control circuit for the following:
* A short to ground
* A short to voltage
* An open circuit
* An open relay coil
* An internally shorted or excessively low resistance relay coil
When the ECM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.
Conditions for Running the DTC
* The ignition voltage is between 11-18 volts.
* The engine speed is less than 600 RPM.
* The ECM driver transitions from ON to OFF or from OFF to ON.
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
* A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
* The DTC can be cleared by using a scan tool.
Circuit/System Testing
The A/C Compressor Clutch Relay is located in the Underhood BEC.
1. Ignition OFF, disconnect the A/C Compressor Clutch Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the A/C Compressor Clutch Relay control circuit terminal 87, and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the ignition circuit, relay coil feed circuit, terminal 85 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 the ignition circuit fuse is open, test or replace the a/c compressor clutch relay.
4. Verify that a test lamp illuminates between the relay B+ circuit, terminal 30, and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, test or replace the a/c compressor clutch relay.
5. Disconnect the harness connector at the A/C Compressor Clutch Coil.
6. Test for less than 1 ohm of resistance between the A/C Compressor Clutch Coil ground circuit terminal 86 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 3-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87 of the A/C Compressor Clutch Relay. Verify the A/C Compressor Clutch Relay is activated.
• If the A/C Compressor Clutch Relay does not activate, test the control 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 coil side of the A/C Compressor Clutch Relay ignition circuit terminal 85, and the control circuit terminal 86.
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.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)