2010 Cadillac CTS Sedan AWD V6-3.0L Page 1556
DTC P0645, P0646, or P0647
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure
Instructions) provides an overview of each diagnostic category.
DTC Descriptors
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
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 CLTCH 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 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/Diagrams/Electrical Diagrams)
