OK, 645 is for the clutch relay or a bad PCM.
Roy
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.
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 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 (See: Heating and Air Conditioning > Electrical > HVAC Schematics)
Connector End View Reference
Component Connector End Views (See: Vehicle > Connector Views)
Description and Operation
* Air Temperature Description and Operation (See: Heating and Air Conditioning > Components > Air Temperature Description and Operation)
* Air Delivery Description and Operation (See: Heating and Air Conditioning > Components Air Delivery Description and Operation)
Electrical Information Reference
* Circuit Testing (See: Vehicle > Component Tests and General Diagnostics)
* Connector Repairs (See: Vehicle > Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (See: Vehicle > Component Tests and General Diagnostics)
* Wiring Repairs (See: Vehicle > Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (See: Vehicle > Programming and Relearning) 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 CLTCH relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay coil control circuit terminal 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 relay coil B+ circuit terminal and ground.
If the test lamp does not illuminate, Refer to DTC B1428 (See: A L L Diagnostic Trouble Codes ( DTC ) > B Code Charts > B1428).
4. Connect a test lamp between the relay coil B+ circuit terminal and the relay coil control circuit terminal.
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, 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 CLTCH relay.
Component Testing
1. Ignition OFF, disconnect the A/C CLTCH relay.
2. Test for 60-180 ohms of resistance 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 of resistance between terminals 30 and 87.
If greater than the specified range, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification (See: A L L Diagnostic Trouble Codes ( DTC ) > Verification Tests) after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) (See: Power Distribution Relay > Removal and Replacement > Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (See: Power Distribution Relay > Removal and Replacement > Relay Replacement (Within an Electrical Center))
* Control Module References (See: Vehicle > Programming and Relearning) for ECM replacement, setup, and programming
Thursday, July 25th, 2019 AT 5:23 AM
