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.

Real-world scan data

Seen in

1,161

scans in the past year

Found in

0.2%

of scans

0.3%

of scans that found faults

Appears alongside · share of P0651 scans

P0641in 63.2% of scans

P0226in 32.5% of scans

P0657in 31.5% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P0651 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX