P0641 - SENSOR REFERENCE VOLTAGE A CIRCUIT OPEN

This code (P0641 OBDII) is thrown when the PCM notices an open circuit in the reference voltage circuit “A”. The reference voltage circuit “A” is the circuit that supplies a voltage to the sensors that control the transmission train. All the sensors and modules in this circuit are interconnected through the CAN bus system (Control Area Network).

If there is an open circuit in the reference voltage circuit “A”, all these sensors, modules and subsystems that share this circuit may be faulty. Usually, this code is accompanied by other fault codes.

• MIL light is on.
• Changes during driving can be delayed or erratic.
• The transmission may not make the changes.
• Transfer box failure to shift from high to low.
• The speedometer may be inoperative.

The diagnostic code P0641 OBD2 is set due to the following causes:

• Open circuits or connectors.
• Fuse links or the fuses themselves in bad condition.
• The system's power relay may be defective.
• A sensor in bad condition.

For proper diagnosis and resolution of the fault code P0641 OBDII, you must do the following:

• Check the system fuses, as well as the fuse links with the circuit at full load. If you find any blown fuses, you should replace them.
• Inspect the cables and respective connectors related to the sensor system. If you notice that one of these components is worn or has corrosion, you should replace it.
• Use an automotive scanner to erase the code and see if it comes back.
• If the code returns, use a Digital Volt-Ohm Meter and check the reference voltage, as well as the ground circuit on the sensor. Generally, the volts should be 5 as well as a connection on the sensor connector.
• Test the continuity and resistance of the sensor. Consult vehicle information for test specifications. If they do not match the values obtained, repair and, if necessary, replace the sensor.