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Technical Description of OBD-II Trouble Code
Control Circuit for A/C Clutch Relay
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from GM, Chrysler, Chevrolet, Dodge, Jeep, Cadillac, Ford, Ram, etc. Although it is a generic code, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
The P0645 OBD-II trouble code is associated with the control circuit for the air conditioning (A/C) clutch relay. When the Powertrain Control Module (PCM) or one of the other supporting control modules detects improper signals within the A/C clutch relay control electrical circuit, code P0645 will be set. Depending on the vehicle and the specific malfunction, this code may be set as many as eight times before the check engine light illuminates.
The purpose of the A/C clutch relay control circuit is to regulate the operation of the air conditioning. It does this by supplying power to the A/C clutch to engage the A/C compressor. Depending on the specific vehicle, this circuit can be quite complex and may involve several control modules.
Code P0645 is set by the PCM when it detects a general malfunction in the air conditioning relay control circuit.
What is the severity of this DTC?
The severity of this code can range from just an illuminated check engine light with the air conditioning functioning properly to the air conditioning running poorly or not working at all.
What are some of the symptoms of the code?
Symptoms of a P0645 trouble code may include:
What are some of the common causes of the code?
Causes for this P0645 code may include:
What are some P0645 troubleshooting steps?
The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins (TSB’s) for the specific vehicle by year, model, and power plant. In some circumstances, this can save a lot of time in the long run by pointing you in the right direction.
The second step is a thorough visual inspection to check the associated wiring for obvious defects such as scraping, rubbing, bare wires, or burn spots. Next, check the connectors and connections for security, corrosion, and damaged pins. This process must include all wiring connectors and connections to components, including control modules and ground straps. This circuit can be very complex and may involve several relays, fuse-able links, and fuses in some circumstances.
Advanced Steps
The advanced steps become very vehicle specific and require the appropriate advanced equipment to perform accurately. These procedures require a digital multimeter and the specific technical references for the vehicle. Voltage requirements will vary based on the specific year and model of the vehicle.
Voltage Checks
The voltage check process for this circuit requires troubleshooting guidelines that are specific and in the proper sequence. The optional equipment on the involved automobile 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 possible supporting control modules listed above.
If this process identifies the absence of a power source or ground, continuity testing may be required to check the integrity of the wiring, control modules, and other components. All of the control module ground straps may need to be included in this process. Continuity tests should always be performed with the power removed from the circuit, and the normal readings for wiring and connections should be 0 ohms of resistance unless otherwise specified by the technical data. Resistance or no continuity is an indication of faulty wiring that is open or shorted and must be repaired or replaced.
What are some common repairs for this code?
Common mistakes may include:
The most common mistake when diagnosing the P0645 code is to misdiagnose the symptoms and codes. This is because of the complexity involved. Replacing air conditioning components when damaged wiring, ground straps, or another component is the problem is very common with this code.
Hopefully, the information in this article has been helpful in pointing you in the right direction to correct the problem with your A/C clutch relay control circuit fault code. This article is strictly informational, and the specific technical data and service bulletins for your vehicle should always take priority.
Professional Service
Of course, we always recommend seeking professional mechanical assistance to solve this issue. However, if for some reason this seems impossible, then we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you would like this service, please upload your ECU file to our portal.
