Parts
$0-1,000
P0651 — Sensor Reference Voltage 'B' Circuit Open / Out of Range
CAUTIONIs it safe to drive? Usually driveable, but get it diagnosed soon; it can worsen, hurt fuel economy, or fail emissions if ignored.
What P0651 means
Same as P0641 but the second (B) 5-volt sensor reference circuit. A short or open on that reference affects the sensors it supplies and may cause limp mode.
Most likely causes (in order)
- Shorted sensor on the B reference circuit
- Chafed/shorted wiring
- Failed PCM reference output
- Poor ground
Symptoms you might notice
- check engine light
- multiple sensor codes
- reduced power
What to check first
Isolate by unplugging sensors fed by the B reference; check wiring for shorts to power/ground.
Repair cost & difficulty
Labor
1-3 hr
Difficulty
DIY-friendly