P0645

DTC P0645

DTC DESCRIPTOR

DTC P0645
Air Conditioning A/C Clutch Relay Control Circuit

DIAGNOSTIC FAULT INFORMATION






IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

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. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. When this DTC is set the affected driver is disabled.

CONDITIONS FOR RUNNING THE DTC
- The ignition voltage is between 9 and 18 volts.
- The engine speed is more than 80 RPM.
- The ECM driver transitions from ON to OFF or from OFF to ON.

CONDITIONS FOR SETTING THE DTC
The ECM detects one of the following:
- A short to ground
- A short to voltage
- An open circuit or relay
- An internally shorted or excessively low resistance relay coil

ACTION TAKEN WHEN THE DTC SETS
- The A/C is inoperative.
- The (MIL) indicator lamp will not illuminate.
- 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.
- Using a scan tool can clear the DTC

DIAGNOSTIC AIDS

IMPORTANT:
- Be sure to verify that the ECM engine grounds are secure and clean.
- If DTC P0645 cannot be duplicated, reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.
- If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics

CIRCUIT/SYSTEM VERIFICATION
1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With the scan tool, command the A/C Relay ON and OFF in the ECM Special Functions scan tool data list.

CIRCUIT/SYSTEM TESTING
1. The A/C relay turns ON and OFF inspect the system for intermittent conditions and poor connections.
2. The A/C relay does not turn ON and OFF. Turn OFF the ignition, disconnect the A/C compressor clutch relay, turn the ignition back ON, test for power on the control side battery positive circuit.
- If the test lamp still does not illuminate repair the control side battery positive circuit.
3. If the test lamp illuminates connect the test light between the control side battery positive circuit and the ECM control circuit. Start the engine, with the scan tool turn the A/C relay ON and OFF.
4. If the test lamp illuminates inspect for a poor connection on the A/C compressor clutch circuit at the point no problem is found replace the A/C clutch relay.
5. The test lamp does not illuminate test the control circuit for poor connections or intermittent conditions.
- If a problem is not found replace the ECM.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for ECM replacement, setup, and programming.