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P0643 is a diagnostic trouble code (DTC) for "Sensor Reference Voltage “A” Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0643 code is stored in the PCM when a fault is detected in the sensor reference voltage A circuit.
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.
The causes of the P0643 code may include:
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:
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.
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.
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.
In order to repair the P0643 code, a technician may attempt any of the following:
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