What does code P0641 mean?
Code P0641 stands for Sensor Reference Voltage 'A' Circuit Open.
The vehicle's computer, the powertrain control module (PCM), supplies a reference voltage to many of the onboard sensors. Typically, this reference signal is 5-Volts. The sensors then verify this voltage signal in accordance with whatever they're measuring and send it back to the PCM.
Although the external sensor reference circuits are independent of one another, they are sometimes connected inside the PCM. For example, on some General Motors vehicles, the engine oil pressure sensor and manifold absolute pressure sensor are bussed together inside the PCM. This can cause one sensor's 5-Volt reference circuit to affect the other.
Code P0641 indicates the PCM has detected voltage is out of specification on the 5-Volt reference circuit. The 'A' part of the code indicates the problem is with the number one sensor, if more than one sensor is in question.
Note: Typically, the manufacture's repair information will indicate which sensor circuits are affected when code P0641 is stored. For example, on one vehicle, code P0641 may indicate a problem with the power take off (PTO) reference circuit. On another vehicle, it may refer to the fuel pressure sensor.
P0641 symptoms
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Common causes for P0641
Code P0641 is typically caused by one of the following:
- A faulty sensor
- Wiring issues
- A problem with PCM
How to diagnose and repair P0641
Perform a preliminary inspection
Sometimes P0641 can pop up intermittently. This is especially true if the code is a history code and not current. Clear the code and see if it returns. If it does, the next step is to perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.
Check the circuit
After the primary inspection the reference circuits should be checked. This can be done using a digital multimeter (DMM). A sensor typically has two or three wires going to it, one of which is the reference signal. The meter should show a good reference voltage being supplied to the sensor(s) by the PCM. If not, the wiring between the sensor and PCM should be checked and repaired as needed.
