2010 Cadillac CTS Sedan AWD V6-3.0L Page 1558
瀚慖f 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.
瀚慖f greater than the specified range, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.
* Air Conditioning Compressor Replacement (LF1, LLT) (See: Heating and Air Conditioning/Compressor HVAC/Service and
Repair/Removal and Replacement)Air Conditioning Compressor Replacement (LSA) (See: Heating and Air Conditioning/Compressor
HVAC/Service and Repair/Removal and Replacement)
* Relay Replacement (Attached to Wire Harness) (See: Power and Ground Distribution/Power Distribution Relay/Service and Repair/Relay
Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (See: Power and Ground Distribution/Power
Distribution Relay/Service and Repair/Relay Replacement (Within an Electrical Center))
* Control Module References (See: Testing and Inspection/Programming and Relearning) for HVAC control module and ECM replacement,
setup, and programming
P0647
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.
