Diagnostic Instructions
DTC Descriptor
DTC P0645: Air Conditioning A/C Clutch Relay Control Circuit
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.
Reference Information
Schematic Reference
HVAC Schematics
Connector End View Reference
HVAC Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the A/C Relay.
- 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. |
- 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. |
- Connect a test lamp between the ignition circuit terminal, and the relay control circuit terminal.
- 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. |
- If all circuits test normal, test or replace the A/C Clutch Relay.
Component Testing
- Ignition OFF, disconnect the A/C Clutch Relay.
- Test for less than 200 ohms between terminals 85 and 86.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
- Test for infinite resistance between the following terminals:
| ⇒ | If less than infinite resistance, replace the relay. |
- Test for less than 2 ohms between terminals 30 and 87A.
| ⇒ | If greater than 2 ohms, replace the relay. |
- 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 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.
