P0651: Sensor reference voltage B: circuit open or faulty
The ECU detects a fault in its second 5 volt supply for sensors. Usually a shorted sensor or damaged wiring.
| Code | P0651 |
|---|---|
| System | Engine and transmission |
| Group | P06xx, Control unit and auxiliary outputs |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0651 means
Many ECUs have several 5 volt supply lines for sensors, and this is the one called reference B. This code means that line is not right. Which sensors depend on reference B is up to each manufacturer; it often includes one of the accelerator pedal or throttle sensors.
Most common causes
- One sensor on that line with an internal short
- A sensor plug loose, wet or corroded
- Reference B wire broken or chafed
- Poor sensor earth
- Internal ECU fault
Symptoms
- Engine warning light on
- Several sensor codes at once
- Limp mode or poor accelerator response
- Hard starting
Can you drive with P0651?
With care The car may go into limp mode with little power. Drive carefully and only as far as a garage.
Open the bonnetthe in-depth explanation
How to check it
Note which other codes appear with this one: they show which sensors share reference B. A garage can measure whether the voltage returns to 5 volts as each sensor is unplugged.
How to read and clear P0651 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0651 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P064D The internal control unit lambda sensor processor (bank 1) gives readings
- P064E The internal control unit lambda sensor processor (bank 2) gives readings
- P064F An unauthorized software calibration that is not original equipment has been
- P0650 Malfunction indicator lamp (MIL) control: circuit fault
- P0652 Sensor reference voltage B: circuit low
- P0653 Sensor reference voltage B: circuit high
- P0654 The engine speed output has an electrical fault
- P0655 The engine hot light output control has an electrical fault
- P0600 Serial communication link fault
- P0601 Internal control module memory checksum error
- P0602 Control module programming error
- P0603 Internal control module keep alive memory (KAM) error
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Accelerator.
What does code P0651 mean?
Many ECUs have several 5 volt supply lines for sensors, and this is the one called reference B. This code means that line is not right. Which sensors depend on reference B is up to each manufacturer; it often includes one of the accelerator pedal or throttle sensors.
Can you drive with P0651?
The car may go into limp mode with little power. Drive carefully and only as far as a garage.
How do you clear P0651?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0651 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
