P0645
DTC P0645
DTC Descriptor
DTC P0645
- Air Conditioning A/C Clutch Relay Control Circuit
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
Circuit/System Description
Ignition voltage is supplied directly to the air conditioning (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.
Conditions for Running the DTC
* The ignition voltage is between 9 and 18 volts.
* The engine speed is more than 80 RPM.
* The ECM A/C Compressor Clutch Relay Control driver circuit transitions between ON to OFF or from OFF to ON.
Conditions for Setting the DTC
The ECM detects one of the following:
* A short to ground on the A/C Compressor Clutch Relay Control Circuit
* A short to voltage on the A/C Compressor Clutch Relay Control Circuit
* An open circuit on the A/C Compressor Clutch Relay Control Circuit or relay
* An internally shorted or excessively low resistance A/C Clutch Relay Coil
Action Taken When the DTC Sets
* The A/C clutch relay is commanded OFF.
* The conditions for which the DTC was set will be stored in the Failure Records data only. No information will be stored as Freeze Frame data.
Conditions for Clearing the DTC
The history DTC will clear after 40 fault-free ignition cycles.
Circuit/System Testing
1. Ignition OFF, disconnect the A/C Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay control circuit terminal 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, terminal 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 all components connected to the ignition circuit and replace as necessary.
4. Connect a test lamp between the ignition circuit terminal, and the relay control circuit terminal.
5. 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.
6. If all circuits test normal, test or replace the A/C Clutch Relay.
Component Testing
1. Ignition OFF, disconnect the A/C Clutch Relay.
2. Test for less than 200 ohms of resistance between terminals 85 and 86.
• If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If less than infinite resistance, replace the relay.
4. Test for less than 2 ohms of resistance between terminals 30 and 87A.
• If greater than 2 ohms, replace the relay.
5. Install a 20-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.
• If greater than 2 ohms, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
* Control Module References for ECM replacement, setup, and programming.
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center) Verification Tests