Powertrain, generic · Computer and auxiliary outputs

P0642 Sensor Reference Voltage A Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

5 V wire or sensor shorted to ground
Internal short in a supplied sensor (e.g. pressure sensor)
Chafed harness or water ingress
Module reference regulator faulty

Symptoms

  • Check engine light
  • Limp mode with reduced power
  • Many codes from several sensors at once
  • Possibly starting or boost problems

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–4 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

P0641P0643P06A6P0652P0698

References: law.cornell.edu, fordservicecontent.com, newtonnet.co.uk, saabwisonline.com.