P0651 - SENSOR REFERENCE VOLTAGE B CIRCUIT OPEN

OBDII DTC P0651 indicates that the vehicle’s computer has detected an open circuit on a particular sensor which is designated “B”. When the circuit is open, it may also indicate that it is absent. This sensor is associated with the automatic transmission or a differential. It is usually accompanied by another specific sensor code. This code indicates is that the circuit is open.

The reference voltage, which is usually 5 volts, is applied to the sensor via a switched circuit, plus a ground signal. Its resistance may be variable depending on the conditions to complete a circuit and provide the Powertrain Control Module (PCM) with an input voltage signal. If the PCM does not receive such a voltage signal, it is considered an open circuit.

• Illuminated check engine light.
• Transmission malfunctions when shifting.
• Transmission malfunction.
• Malfunctioning speedometer.

Reasons for setting the P0651 OBD2 diagnostic code:

• The circuit may be open or a bad condition of the wires or connectors.
• There may be blown fuses.
• The system power relay may be faulty.
• The sensor may be faulty.

To troubleshoot the P0651 OBDII fault code, consider the following:

• Use the vehicle information source to determine both the location and function of the sensor. Then, inspect the fuses and their links to the fully loaded circuit. Replace blown fuses.
• Check the system wiring and connectors for damage. Replace if necessary.
• By using a multimeter, test the reference voltage and ground signal for the sensor. Also check the resistance, circuit, and continuity between the sensor and the PCM. Make the respective adjustments.