Powertrain, generic · Computer and auxiliary outputs

P0651 Sensor Reference Voltage B Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The engine module feeds several sensors (camshaft, pedal, pressure sensors) from separate regulated 5 V reference circuits; 'B' is circuit 2. A short at one sensor pulls the whole reference down, so every sensor on it reports at once – unplug them one by one until the reference returns to 4.8–5.2 V. P0651 is the general code for circuit B. GM puts all faults into it: reference outside 4.875–5.125 V or jumping, 19 of 39 counts or 0.19 s in a row, with the lamp in the first trip (2018; GM's 2006 V6 used 10 s and two trips). GM Europe's 2.0 L turbo feeds all four camshaft sensors and pedal sensor 1 from it and also uses P0652/P0653 (1 s or 10 s cumulative). Ford reports reference B only as range/performance P06A7. Expect limp mode if the pedal sensor is affected, and starting problems or stalling if camshaft sensors are.

Likely causes

Short in the wire or sensor of a connected sensor (camshaft, pedal, pressure)
Chafing or water in harness or connector
A sensor signal wire shorted to voltage
Module internal voltage regulator

Symptoms

  • Check engine light
  • Several sensor codes at once (camshaft, pedal, pressure)
  • Limp mode, reduced power
  • Starting problems or stalling

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

sensor reference voltage circuitsensor wiringengine control module

Related codes

P0652P0653P0641P0697P06A7P2127

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com.