For 1990-2009 cars

### Diagnostic Instructions

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

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

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P1545: Air Conditioning (A/C) Clutch Relay Control Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
A/C Relay Switch B+ | 2 | 2 | -- | --
A/C Relay Coil Ignition | 2 | 2 | -- | --
A/C Relay Control | P1545 | P1545 | P1545 | --
A/C Clutch Control | 2 | 2 | 1 | --
A/C Compressor Clutch Ground | -- | 2 | -- | --
1. A/C Clutch Always Engaged 2. A/C Clutch Inoperative

### Circuit/System Description

When the A/C switch is pressed, the HVAC control assembly sends a serial data message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.

### Conditions for Running the DTC

• | The ignition voltage is between 9 and 18 volts.

• | The engine speed is more than 600 RPM.

• | An A/C request is made.

### 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 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

Component Connector End Views

#### Description and Operation

• | Air Delivery Description and Operation

• | Air Temperature Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the A/C relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 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 85 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 ignition circuit fuse is open, test or replace the relay.

4. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
5. 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.

⇒ | 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 relay.

### Component Testing

1. Ignition OFF, disconnect the A/C 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 after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for ECM replacement, setup, and programming