P0651: Sensor Reference Voltage B Circuit/Open

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.

Symptoms

• Check engine light
• Several sensor codes at once (camshaft, pedal, pressure)
• Limp mode, reduced power
• Starting problems or stalling

Most likely causes

• Short in the wire or sensor of a connected sensor (camshaft, pedal, pressure)
• Chafing or water in harness or connector
• A sensor signal wire shorted to voltage
• Module internal voltage regulator

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery and grounds
2. Check the continuity of the wire between the component and the control module.
3. Clear the code and see if it returns
4. If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
5. Check whether a software update is available
6. Do not replace the control module without a full diagnosis

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P0651 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 6: Control modules and outputs
• 51: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0651?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P0651?

The most common causes are: short in the wire or sensor of a connected sensor (camshaft, pedal, pressure); chafing or water in harness or connector; a sensor signal wire shorted to voltage.

Related codes

• P0652Sensor Reference Voltage B Circuit Low
• P0653Sensor Reference Voltage B Circuit High
• P0641Sensor Reference Voltage A Circuit/Open
• P0697Sensor Reference Voltage C Circuit/Open
• P06A7Sensor Reference Voltage B Circuit Range/Performance
• P2127Throttle/Pedal Position Sensor/Switch E Circuit Low

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• saabwisonline.com: dtc p0641 p0643 p0651 p0653 or p0697 p0699 ecm

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.