P0651Sensor Reference Voltage B Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- The engine module feeds several sensors (camshaft, pedal, pressure sensors) from separate regulated 5 V reference circuits; 'B' is circuit 2. A short at one sensor pulls the whole reference down, so every sensor on it reports at once – unplug them one by one until the reference returns to 4.8–5.2 V. P0651 is the general code for circuit B. GM puts all faults into it: reference outside 4.875–5.125 V or jumping, 19 of 39 counts or 0.19 s in a row, with the lamp in the first trip (2018; GM's 2006 V6 used 10 s and two trips). GM Europe's 2.0 L turbo feeds all four camshaft sensors and pedal sensor 1 from it and also uses P0652/P0653 (1 s or 10 s cumulative). Ford reports reference B only as range/performance P06A7. Expect limp mode if the pedal sensor is affected, and starting problems or stalling if camshaft sensors are.
- What you may notice
- Check engine light
- Several sensor codes at once (camshaft, pedal, pressure)
- Limp mode, reduced power
- Starting problems or stalling
- Likely causes
- LikelyShort in the wire or sensor of a connected sensor (camshaft, pedal, pressure)
- PossibleChafing or water in harness or connector
- PossibleA sensor signal wire shorted to voltage
- RareModule internal voltage regulator
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.