P0643: The sensor reference voltage A circuit reads too high

Sensor reference voltage A circuit high

Severity: Inspect soon

The reference voltage powers several sensors, including the accelerator pedal sensor on some vehicles. A 2006 Quest owner had the engine shut down at 65 mph with this code, so it should be checked soon.

It gets more serious if:

Stop: The engine shuts off or loses throttle response while driving. A 2006 Nissan Quest owner reports a complete shutdown at highway speed with P0643 on the dealer's invoice. Do not keep driving; have it checked.

Source: how we rate severity

P0643 in short

P0643 means the computer sees the sensor reference voltage A circuit too high. The cause listed is a wiring short to positive. On a 2006 Nissan Quest the dealer tied it to the accelerator pedal sensor after a highway shutdown. Get it checked soon.

The engine computer supplies a steady reference voltage, usually 5 volts, to several sensors and compares their signals to it. TroubleCodes.net defines P0643 as sensor reference voltage A circuit high and lists a wiring short to positive as the probable cause.

Because several sensors can share one reference feed, a fault on the feed or in one of the sensors on it can raise the voltage and affect more than one reading.

On a 2006 Nissan Quest, the dealer's invoice reads 'P0643 sensor power supply, found APP sensor fault, needs gas pedal assembly' after the vehicle shut off at 65 mph and restarted. That is one vehicle's repair note; the Xterra complaints read for this code give no cause.

Most likely causes

Cause 1: Wiring short to positive on the reference circuit
Common general cause
Why it ranks here
TroubleCodes.net lists a wiring short to positive as the probable cause for a circuit-high reference code.
What would change this
Rises if a reference wire is found chafed, or a shared sensor is unplugged and the voltage drops back to normal. Falls if the reference measures normal with all sensors connected.
Cause 2: Accelerator pedal position sensor fault (Nissan Quest)
Supported by vehicle data
Why it ranks here
A 2006 Quest's dealer invoice attributes P0643 to the APP sensor and says the vehicle needs a gas pedal assembly. This is one vehicle, so it may not apply to other models.
What would change this
Rises if disconnecting the pedal sensor restores a normal reference voltage. Falls if the voltage stays high with it disconnected.
How to test the accelerator pedal position sensor

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Read all stored codes and freeze-frame data and note any sensor circuit codes stored with P0643, including pedal and throttle position codes.
Low riskTool: OBD-II scan tool
- IfPedal or throttle sensor codes are stored too
  It meansA shared reference feed or a sensor on it is the likely area.
  Go to step 2
- IfP0643 is stored alone
  It meansCheck the reference circuit wiring.
  Go to step 2
Step 2: Measure the reference voltage at the sensors and unplug sensors one at a time to see whether the voltage returns to normal.
Best left to a shopTool: multimeter, wiring diagram
Warning:Probing the engine computer's wiring can short a circuit and damage the module or set more codes. Have a shop do it with the wiring diagram.
- IfThe voltage drops back when the accelerator pedal sensor is unplugged
  It meansThe pedal sensor is the cause.
  Points to: Accelerator pedal position sensor fault (Nissan Quest)
- IfThe voltage stays high with all sensors unplugged
  It meansLook for a short to power in the wiring.
  Points to: Wiring short to positive on the reference circuit

Symptoms

Check engine light with a stored P0643
Reduced throttle response or reduced power
Engine shuts off while driving, sometimes restarting after a few minutes Gets more serious: stop and have it checked.

How to fix

Step 1: Have a shop read all codes and measure the reference voltage before replacing sensors.

Parts and cost context

Accelerator pedal position sensor:The Quest dealer's repair note names the pedal assembly; confirm with a voltage test first. Labour varies, get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Nissan

2006 · Quest
Supported by vehicle data
A 2006 Quest's dealer invoice reads 'P0643 sensor power supply, found APP sensor fault, needs gas pedal assembly' after a highway shutdown. One complaint, not verified by NHTSA.

All Engine computer (ECM/PCM) codes

P0643 questions

Is it safe to drive with P0643?

Not with confidence. A 2006 Quest owner reports a full shutdown at highway speed with this code. Get it checked soon.

Sources and review

NHTSA complaint ODI 10413403: 2006 Nissan Quest, P0643 sensor power supply, APP sensor fault — NHTSA Office of Defects Investigation (complaint flat file)
P060C, P0615, P062A, P0643 code pages — TroubleCodes.net

Last reviewed: October 16, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Most likely causes

Cause 1: Wiring short to positive on the reference circuit

Cause 2: Accelerator pedal position sensor fault (Nissan Quest)

What to test first

Step 1: Read all stored codes and freeze-frame data and note any sensor circuit codes stored with P0643, including pedal and throttle position codes.

Step 2: Measure the reference voltage at the sensors and unplug sensors one at a time to see whether the voltage returns to normal.