P0642Sensor Reference Voltage A Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- The engine module feeds several sensors (pedal, throttle, pressure and position sensors) from shared, regulated 5 V reference circuits; 'A' is circuit 1. A short on one sensor or its wire pulls down every sensor on that circuit and triggers many follow-up codes – so look for the one faulty sensor or chafed wire, for example by unplugging the sensors one at a time. P0642 means the voltage of reference circuit A is too low – typically the 5 V wire or a connected sensor is shorted to ground. Ford checks continuously from ignition on and sets it below 4.75 V after 5 s; GM Europe's 2.0 L petrol after 1 s or 10 s cumulative, lamp in the first trip. GM North America reports it as P0641. All sensors on the circuit then read near 0 V, with matching 'low' codes. High is P0643, range/performance P06A6.
- What you may notice
- Check engine light
- Limp mode with reduced power
- Many codes from several sensors at once
- Possibly starting or boost problems
- Likely causes
- Likely5 V wire or sensor shorted to ground
- PossibleInternal short in a supplied sensor (e.g. pressure sensor)
- PossibleChafed harness or water ingress
- RareModule reference regulator faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.