P0651
Sensor Reference Voltage B Circuit/Open
Computer output circuit
Generic OBD-II
High
What it means
P0651 means the PCM's 5-volt "B" reference — the supply voltage it feeds to several sensors such as the throttle, MAP, or pedal position sensors — is open or out of range. Because multiple sensors can share one reference, losing it often sets several codes at once and makes the engine run poorly or enter limp mode. A common cause is one shorted sensor pulling the shared reference down, so isolate before replacing the PCM.
High
Can I keep driving? Drivable but may run poorly or enter limp mode, since several sensors can lose their reference at once — get it diagnosed soon.
Common symptoms
What you'll notice
- Check-engine light on, often with several sensor codes together
- Reduced power or hesitation
- Rough idle or stalling
- Erratic gauge or sensor readings
Common causes
Most likely first
- Open or short in the 5-volt reference 'B' circuitLikely
- A shorted sensor pulling the shared reference downCommon
- Corroded or loose connector on the reference circuitCommon
- PCM reference-supply fault (less common)Less often
How to diagnose & fix
Work through it in order
- Read all stored codes — the sensors sharing reference B point to the affected circuit.
- Measure the reference voltage at those sensors; a missing or low 5V confirms the fault.
- Disconnect sensors on that reference one at a time to find a shorted one dragging the circuit down.
- Repair the wiring/connector, or replace the shorted sensor. If the circuit is good, suspect the PCM. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0651?+
Cautiously. Several sensors may share this reference, so the engine can run poorly or drop into reduced-power mode. Have it diagnosed before longer trips.
Can I just clear P0651?+
It returns while the reference circuit is open or shorted. Find the shorted sensor or wiring fault first.
Related codes
Often seen with P0651
Read & clear P0651 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX