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P0645




DTC P0645, P0646, or P0647

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

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/System Description

Ignition 3 voltage is supplied to the mode switch from the blower motor switch. The blower motor switch must be in any position except for OFF for A/C operation. The mode switch must be in one of the following positions for an A/C request:

* MAX A/C

* A/C

* Bi-Level

* Defog

* Defrost

Once the mode switch is in one of these positions, the mode switch applies ignition 3 voltage to the A/C high pressure switch. If the A/C high pressure switch is closed, the voltage will then be applied to the powertrain control module (PCM), for the 8.1L (RPO L18), or engine control module (ECM), for the 6.6L (RPO LLY). The voltage applied to the ECM/PCM is an A/C request signal. The PCM/ECM then monitors the voltage on the A/C low pressure switch signal. If the voltage is low near ground, then the ECM/PCM will enable the A/C compressor clutch relay. The ECM/PCM provides a ground for the relay so it can close it internal contacts.

Conditions for Running the DTC

* The ignition voltage is between 9 and 18 volts.

* The engine speed is more than 800 RPM.

* The ECM/PCM A/C compressor clutch relay control transitions between ON to OFF or from OFF to ON.

Conditions for Setting the DTC

* 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 Electrical DiagramsHVAC Schematics Electrical Diagrams

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Description and Operation

* Air Delivery Description and Operation Air Delivery

* Air Temperature Description and Operation Air Temperature

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

Ignition ON, command the A/C relay ON and OFF with a scan tool. Observe the A/C compressor operation, the A/C compressor clutch should engage and disengage when changing between the commanded states.

Circuit/System Testing

1. Ignition OFF, disconnect the A/C compressor clutch relay.

2. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse/breaker is open, test or replace the A/C compressor clutch relay.

3. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.

4. Command the A/C relay 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/PCM.

• 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/PCM.

5. If all circuits test normal, test or replace the A/C compressor clutch relay.

Component Testing

1. Ignition OFF, disconnect the A/C compressor clutch relay.

2. Test for 60-180 ohms 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 not the specified value, replace the relay.

4. Install a 30-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 the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Control Module References Control Module References for ECM/PCM replacement, setup, and programming

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