Sensor Reference Voltage "B" Circuit Open
P0651 indicates an open circuit in the Sensor Reference Voltage B circuit, which provides stable voltage to engine control sensors. This code means the PCM detected a break or disconnection in the wiring, connectors, or components supplying this reference voltage to sensors that monitor engine parameters.
What You Might Notice
- Check Engine Light illuminated
- Transmission may fail to shift properly between modes
- Engine may run rough or hesitate
- Reduced fuel economy
- Possible limp mode engagement
Most Common Causes
- 1
Open wiring or damaged connector
Broken wires, corroded terminals, or loose connectors in the sensor reference voltage B circuit prevent proper voltage delivery to sensors.
- 2
Blown fuse or fusible link
A faulty fuse protecting the sensor reference voltage circuit has blown, interrupting power to the entire circuit.
- 3
Faulty system power relay
The relay responsible for supplying power to the sensor reference voltage circuit has failed or contacts are corroded.
- 4
Defective sensor or PCM connector
A sensor in the circuit has failed internally, or the PCM connector pins are damaged or corroded, breaking the reference voltage circuit.
How to Diagnose It
- 1
Check Open wiring or damaged connector — Broken wires, corroded terminals, or loose connectors in the sensor reference voltage B circuit prevent proper voltage delivery to sensors.
- 2
Check Blown fuse or fusible link — A faulty fuse protecting the sensor reference voltage circuit has blown, interrupting power to the entire circuit.
- 3
Check Faulty system power relay — The relay responsible for supplying power to the sensor reference voltage circuit has failed or contacts are corroded.
- 4
Check Defective sensor or PCM connector — A sensor in the circuit has failed internally, or the PCM connector pins are damaged or corroded, breaking the reference voltage circuit.
How to Fix It
- 1
Inspect and repair wiring and connectors
Visually inspect the sensor reference voltage B circuit wiring for breaks, pinches, or corrosion. Check all connectors for corrosion, bent pins, or loose contacts. Repair or replace damaged wiring and reconnect loose terminals.
- 2
Replace blown fuse or fusible link
Locate the fuse or fusible link protecting the sensor reference voltage circuit using the fuse diagram. Replace with the correct amperage rating and test for the fault.
- 3
Test and replace power relay if needed
Use a multimeter to test the sensor reference voltage relay for continuity and proper operation. If faulty, replace the relay and verify voltage is restored to the circuit.
- 4
Diagnose and replace faulty sensor
If wiring and relays are intact, use a multimeter to test voltage at each sensor connector in the circuit. Replace any sensor showing no reference voltage or PCM connector if damaged.
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