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. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
A/C CLTCH Relay Coil B+ | B1428 | B1428 | -- | -- |
A/C CLTCH Relay Switch B+ | 2 | 2 | -- | -- |
A/C Compressor Clutch Relay Control | P0645 | P0645 | P0645 | -- |
A/C CLTCH Relay Controlled Output | 2 | 2 | 1 | -- |
A/C Compressor Clutch Ground | -- | 2 | 2 | -- |
1. A/C Clutch Always Engaged 2. A/C Clutch Inoperative | ||||
Circuit/System Description
Ignition voltage is supplied directly to the 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.
Diagnostic Aids
The following conditions must be met in order for the ECM to engage the A/C compressor clutch:
| • | Battery voltage is between 9-18 volts |
| • | Engine coolant temperature (ECT) is less than 123°C (253°F) |
| • | Engine speed is less than 4,760 RPM |
| • | Engine speed is more than 600 RPM |
| • | A/C high side pressure is between 2929-269 kPa (425-39 psi) |
| • | Throttle position is less than 100 percent |
| • | Evaporator temperature is greater than 0°C (32°F) |
| • | ECM/PCM does not detect excessive torque load |
| • | ECM/PCM does not detect insufficient idle quality |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
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
- Ignition OFF, disconnect the A/C CLTCH relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal and ground.
- Verify that a test lamp illuminates between the relay coil B+ circuit terminal and ground.
- Verify that a test lamp illuminates between the relay switch B+ circuit terminal and ground.
- Disconnect the harness connector at the A/C compressor clutch.
- Test for less than 1.0 ohm of resistance between the A/C compressor clutch ground circuit terminal B and ground.
- Connect the harness connector at the A/C compressor clutch.
- Connect a 10A fused jumper wire between the relay switch B+ circuit terminal and the control circuit terminal. Verify the A/C compressor clutch is activated.
- Connect a test lamp between the relay coil B+ circuit terminal and the A/C compressor clutch relay control circuit terminal.
- 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 all circuits test normal, test or replace the A/C CLTCH relay.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If the test lamp does not illuminate, refer to DTC B1428 . |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ ignition circuit fuse is open, test the control circuit terminal for a short to ground. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the A/C compressor clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the A/C compressor. |
| ⇒ | 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. |
Component Testing
Relay Test
- Ignition OFF, disconnect the A/C CLTCH relay.
- Test for 60-180 ohms of resistance between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- 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 of resistance between terminals 30 and 87.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 30 and 85 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
