Description of the P0646 fault code.
OBD2 Error Codes

P0646 A/C Compressor Clutch Relay Control Circuit Low

26.05.2022 /

P0646 – OBD-II Trouble Code Technical Description

DTC P0646 indicates that the A/C compressor clutch relay control circuit voltage is too low (compared to the manufacturer's specification).

What does the fault code mean P0646?

Trouble code P0646 indicates that the A/C compressor clutch relay control circuit voltage is too low compared to the manufacturer's specification. This error indicates a problem with the A/C compressor clutch relay. It may be detected by the powertrain control module (PCM) or one of the vehicle's auxiliary control modules.

Fault code P0646.

Possible reasons

Trouble code P0640 indicates a problem in the intake air heater electrical circuit, possible causes of this fault are:

  • Defective intake air heater.
  • Poor connection or break in the wires and connectors associated with the intake air heater.
  • Incorrect operation of the engine control module (ECM/PCM), which controls the intake air heater.
  • Faulty air temperature sensor or other related sensor.
  • Problems with mass air flow in the intake system.
  • Incorrect data from other sensors that may affect the operation of the intake air heater.

This is just a general list of possible causes, and specific problems may vary depending on the specific model and brand of vehicle. To accurately determine the cause, additional diagnostics must be performed.

What are the symptoms of a fault code? P0646?

Symptoms for DTC P0646 may include the following:

  • Malfunctioning or improper operation of the air conditioner: It is possible that the vehicle's air conditioner may not work properly or not turn on at all due to insufficient voltage in the compressor clutch relay control circuit.
  • Intermittent problems with the operation of the air conditioner: Periodic shutdown or uneven operation of the air conditioner may occur due to unstable voltage in the control circuit.
  • Check Engine Light: If there is a problem with the A/C compressor clutch relay control circuit, the Check Engine light on the dashboard may come on.
  • Reduced vehicle performance: Inadequate cooling of the air inside the vehicle can lead to discomfort while driving.
  • High Engine Temperature: If the air conditioner does not operate properly due to insufficient voltage in the control circuit, it may cause the engine temperature to become high due to insufficient cooling.

It is important to note that specific symptoms may vary depending on the specific model and make of the vehicle, as well as the extent and nature of the problem.

How to diagnose a fault code P0646?

To diagnose DTC P0646, follow these steps:

  1. Checking electrical connections: Check the condition of all electrical connections associated with the A/C compressor clutch relay control circuit. Make sure all connectors are securely connected and there are no signs of corrosion or damage to the wires.
  2. Voltage test: Using a multimeter, measure the voltage at the A/C compressor clutch relay control circuit. Make sure the voltage meets the manufacturer's specifications. If the voltage is too low, it may indicate a wiring or relay problem.
  3. Checking the air conditioning compressor clutch relay: Check the condition and functionality of the air conditioning compressor clutch relay. Check that the relay is functioning correctly and there is no sign of wear or damage.
  4. Checking the air conditioning compressor: Check the operation of the air conditioning compressor itself. Make sure it turns on when power is applied and works without problems.
  5. Diagnostics using a car scanner: Using a vehicle scanner, diagnose all control modules associated with the A/C compressor clutch relay control circuit. Check for other trouble codes that may be associated with this problem.
  6. Checking wiring and sensors: Check the condition of the wiring and sensors related to the air conditioning system. Make sure the wires are not broken and the sensors are functioning correctly.

After diagnosing and identifying the cause of the malfunction, the necessary repairs or replacement of components should be made according to the identified problems.

Diagnostic errors

When diagnosing DTC P0646, the following errors may occur:

  • Insufficient checking of electrical connections: The error may be due to incorrect or insufficient checking of electrical connections. If the wires are not securely connected or are corroded, this can result in low voltage in the circuit.
  • Incorrect interpretation of measurement results: Incorrect interpretation of voltage measurements using a multimeter may lead to incorrect conclusions. It is necessary to ensure that the measurements are correct and accurate.
  • Skip checking other components: The error may occur if other components related to the operation of the air conditioning compressor clutch relay, such as the compressor itself, sensors, relays and others, have not been checked.
  • Ignoring diagnostic codes: If other diagnostic codes related to the air conditioning system or other systems are ignored, this may result in an incomplete diagnosis and the problem being missed.
  • Incorrect use of the car scanner: Incorrect use of the vehicle scanner or incorrect selection of diagnostic parameters can also lead to diagnostic errors.

To prevent errors when diagnosing the P0646 trouble code, you must check for all possible causes, pay attention to detail, and correctly interpret measurement and diagnostic data.

How serious is the fault code? P0646?

Trouble code P0646, which indicates the A/C compressor clutch relay control circuit voltage is too low, can be serious, especially if it is not detected and corrected. Low voltage may cause the air conditioner to not operate properly and therefore not cool the cabin during hot weather.

Although the lack of air conditioning may be an inconvenience, it is not a critical safety issue. However, if the low voltage is caused by other problems in the vehicle's electrical system, it can lead to more serious consequences, such as failure of other critical systems, such as the battery charging system or fuel injection system.

Therefore, although the problem that caused the P0646 code may be relatively less serious individually, it is important to take into account its possible consequences and ensure that the problem is corrected in a timely and correct manner.

What repair will help eliminate the code? P0646?

To resolve DTC P0646, follow these steps:

  1. Checking electrical connections: Check all electrical connections, including connectors and wires associated with the A/C compressor clutch relay. Make sure they are securely connected and show no signs of corrosion or damage.
  2. Checking the relay itself: Check the A/C compressor clutch relay for operation. It may need to be replaced if any faults are found.
  3. Voltage test: Measure the control circuit voltage to ensure it meets the manufacturer's specifications. If the voltage is too low, the cause of the problem must be found and corrected.
  4. Replacing wiring or sensor: If damaged wires or sensors are found, they should be replaced.
  5. Diagnostics and repair of other systems: If the low voltage problem is caused by other problems in the vehicle's electrical system, such as problems with the battery or alternator, further diagnosis and repairs will need to be made.

After completing these steps, it is recommended that you perform an air conditioning system test and additional diagnostics to ensure that the P0646 code no longer appears.

What is P0646 Engine Code [Quick Guide]

P0646 – Brand-specific information

Trouble code P0646 indicates that the A/C compressor clutch relay control circuit voltage is too low, and the code for some specific vehicle brands is:

For your specific vehicle, it is recommended that you consult your owner's manual or service manual for more detailed information about fault codes and their meanings.

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