Code Definition

P0651 — Sensor Reference Voltage “B” Circuit/Open

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Holden

About P0651

P0651 is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Holden vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0651 is stored, the module has detected an open (broken or disconnected) electrical path in the monitored circuit; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0651 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The powertrain control module (PCM) supplies a regulated reference voltage, typically 5V, on its B reference circuit to feed several sensors such as the MAP, TPS, or pressure sensors that share that supply. The PCM monitors this circuit for correct voltage and continuity so it can trust the readings from every sensor on it. DTC P0651 is set when the PCM detects the B reference voltage is missing or has fallen below the low threshold for longer than the defined dwell time, indicating the circuit is open or disconnected. Because many sensors can share one reference, an open here often sets sever...

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