Powertrain, generic · Computer and auxiliary outputs

P0643 Sensor Reference Voltage A Circuit High

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. P0643 means the voltage of reference circuit A is too high – the 5 V wire is shorted to battery voltage or to a higher potential, for example a sensor signal wire shorted to voltage. Ford sets it above 5.25 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. Sensors then read too high, and battery voltage on the reference can damage them. Low is P0642.

Likely causes

5 V wire shorted to battery voltage
Signal wire of a supplied sensor shorted to voltage
Sensor faulty internally
Module faulty

Symptoms

  • Check engine light
  • Limp mode with reduced power
  • Several 'high' sensor codes
  • Implausible readings (pressure, pedal)

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

P0641P0642P06A6P0653P0699

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