What Does It Mean?
This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles (1996-newer). This may include, but is not limited to, vehicles from GM, Chrysler, Chevrolet, Dodge, Jeep, Cadillac, Ford, Ram, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
The OBD-II fault code P0645 is associated with the A/C clutch relay control circuit. When the Powertrain Control Module (PCM) or one of the other supported control modules detects incorrect signals in the A/C clutch relay control electrical circuit, code P0645 is set. Depending on the vehicle and the specific malfunction, this code may be set up to eight times before the Check Engine light illuminates.
The A/C clutch relay control circuit functions to control the operation of the air conditioning. This is accomplished by providing power to the A/C clutch to engage the A/C compressor. Based on the specific vehicle, this circuit can be very complex and involve multiple control modules.
Code P0645 is set by the PCM when it detects a general malfunction in the A/C relay control circuit.
How Severe Is This DTC?
The severity of this code can range from a simple Check Engine light being on with the A/C functioning correctly to poor performance or no operation at all.
What Are Some of the Symptoms of the Code?
Symptoms of a P0645 fault code may include:
A/C operating poorly
Air conditioning not working at all
Check Engine light illuminated
What Are Some of the Common Causes of the Code?
Causes
of this P0645 code may include:
Faulty A/C clutch relay
Faulty A/C clutch
Broken control module ground strap
Faulty control module
Blown fuse or fusible link (if applicable)
Corroded or damaged connector
A/C system with low or excessive refrigerant charge
Faulty or damaged wiring
Faulty A/C compressor
Faulty PCM
What Are the Troubleshooting Steps for P0645?
The first step in the troubleshooting process for any malfunction is to search for Technical Service Bulletins (TSBs) for the specific vehicle by year, model, and powertrain. In some circumstances, this can save a lot of time in the long run by pointing you in the right direction.
The second step involves a thorough visual inspection to check that the associated wiring does not have obvious defects such as chafing, rubbing, bare wires, or burn marks. Next, check the connectors and connections for security, corrosion, and damaged pins. This process should include all wiring connectors and connections to components, including control modules and ground straps. This circuit can be very complex and involve multiple relays, fusible links, and fuses in some circumstances.
Advanced Steps
Advanced steps become very vehicle-specific and require appropriate advanced equipment to perform accurately. These procedures require a digital multimeter and the vehicle-specific technical references. Voltage requirements will be highly dependent on the specific year and model of the vehicle.
Voltage Checks
The voltage checking process for this circuit requires specific troubleshooting guidelines and in the correct order. The optional equipment on the automobile involved will determine the troubleshooting requirements. More options and equipment affect the number of control modules involved in the troubleshooting process. Please refer to the list of supported control modules listed above.
If this process identifies the absence of a power source or ground, continuity tests may be required to check the integrity of the wiring, control modules, and other components. All control module ground straps may need to be included in this process. Continuity tests should always be performed with the power disconnected from the circuit, and normal readings for wiring and connections should be 0 ohms of resistance, unless otherwise indicated by the technical data. Resistance or lack of continuity is an indication of faulty wiring that is open or shorted and must be repaired or replaced.
What Are the Common Repairs for This Code?
Replacement of the A/C clutch relay
Replacement of a blown fuse or fusible link (if applicable)
Cleaning corrosion from connectors
Evacuating and recharging the A/C system
Repairing or replacing wiring
Repairing or replacing ground straps
Replacing a control module
Replacing the A/C clutch
Replacing the A/C compressor
Flashing or replacing the PCM
Common Mistakes Can Include:
The most common mistake when diagnosing P0645 code is misdiagnosing the symptoms and codes. This is due to the complexity involved. Replacing A/C components when there is damaged wiring, ground straps, or another component is a very common issue with this code.
Hopefully, the information in this article has been helpful in pointing you in the right direction to correct the issue with your A/C clutch circuit fault code. This article is strictly informational, and the technical data and service bulletins specific to your vehicle should always take priority.