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P0643 OBD-II Trouble Code: Sensor Reference Voltage “A” Circuit High

Check Engine Light

P0643 code definition

The P0643 code is stored in the PCM when a fault is detected in the sensor reference voltage A circuit.

What the P0643 code means

The sensor reference voltage A circuit is a part of the controller area network, or CAN bus network. This network of sensors and other components work to inform the PCM of the conditions in all the parts of the vehicle. If this particular circuit registers an abnormal voltage reading with the PCM, the P0643 code will be stored.

What causes the P0643 code?

The causes of the P0643 code may include:

  • A faulty or shorted sensor
  • Faulty, loose, or damaged electrical components, such as wiring, harnesses, or connectors
  • Malfunctions within the PCM

What are the symptoms of the P0643 code?

The symptoms of this code can vary from nothing other than the illuminated Check Engine lamp, to not be able to operate the vehicle at all. Symptoms may include:

  • Harsh starting
  • Rough running condition
  • Decreased fuel economy
  • Misfiring engine
  • Lack of power
  • Inability to start the vehicle

How does a mechanic diagnose the P0643 code?

After an OBD-II scanner detects the P0643 code, a technician should always begin with a visual inspection of the electrical components. Any wiring, connectors, or harnesses that are loose, corroded, damaged, or otherwise inoperable should be repaired immediately. After this repair, the code should be cleared from the PCM, and the system should be retested. If the code does not return, it is likely that the electrical components were to blame.

If the code does reappear, the mechanic should use a special scanner, such as an Autohex, to pinpoint the exact malfunction area. This can save time and money, rather than detaching and checking every part of the CAN bus.

Common mistakes when diagnosing the P0643 code

Because this issue relates to the way the PCM receives signals from multiple components, there will likely be other codes stored. Those codes do not represent actual faulty areas, but rather a breakdown in communication due to the fault behind the P0643 code. The most common misdiagnosis is repairing components that were not at fault when other codes are present.

How serious is the P0643 code?

This code represents a very serious issue that should be repaired immediately. Without a properly functioning sensor, the PCM will not be able to monitor and control engine components, and that could lead to more expensive repairs in the future.

What repairs can fix the P0643 code?

In order to repair the P0643 code, a technician may attempt any of the following:

  • Repairing a faulty or shorted sensor
  • Replacing or repairing faulty, loose, or damaged electrical components, such as wiring, harnesses, or connectors
  • Replacing a malfunctioning PCM

Need help with a P0643 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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