P0642 code meaning
Sensor Reference Voltage A Circuit Low
Powertrain system Generic code P06xx codes Check engine light
What P0642 means
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 gasoline 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.
P0642 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0642
- Check engine light
- Limp mode with reduced power
- Many codes from several sensors at once
- Possibly starting or boost problems
Common causes of P0642
- Most likely5 V wire or sensor shorted to ground
- PossibleInternal short in a supplied sensor (e.g. pressure sensor)
- PossibleChafed harness or water ingress
- Less likelyModule reference regulator faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Sensor reference voltage circuitSensor wiringEngine control module
What each part of P0642 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 42 | The exact fault in that area. |
What to do next
- Note P0642 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0642
What does P0642 mean?
P0642 means "Sensor Reference Voltage A Circuit Low". The engine module feeds several sensors (pedal, throttle, pressure and position sensors) from shared, regulated 5 V reference circuits; 'A' is circuit 1. It is a generic code, so it means the same on every make.
Is it safe to drive with P0642?
Drive gently and only to a workshop. With P0642 the car can go into limp mode (reduced power) to protect itself.
Will P0642 fail an emissions test?
Yes, it can. P0642 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0642 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P0642 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.