P06D8: Sensor Reference Voltage F Circuit High

What it means

The voltage in sensor reference circuit F is above the expected range. The affected sensors and resulting symptoms depend on the vehicle.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

Reference circuit F provides regulated voltage to the sensors assigned to it, and the control module monitors whether the rail stays within its expected range. P06D8 sets when the F rail is detected above range, which can disturb readings from multiple connected sensors.

Common causes

Most likely first.

1. Reference rail shorted to supply
2. Connector pins corroded - high contact resistance
3. Supply wire pinched against B+ source

Symptoms

• Check engine light on
• Possible limp mode or no-start
• Multiple follow-up faults across modules
• Reset/relearn may be needed after repair

How to diagnose it

1. Save freeze-frame data and scan for related sensor faults across modules, since several faults appearing together can implicate the shared F supply.
2. Use vehicle-specific wiring information to identify circuit F's sensors and branches, then inspect the harness for a pinched reference wire touching a power feed.
3. Inspect F circuit connectors for corrosion, loose terminals, and signs of heat or water entry that could disrupt the connection.
4. Measure the F reference voltage at the module and sensor connectors under the manufacturer's specified test conditions and compare it with the manufacturer's specification.
5. If it remains high, isolate the branches using the prescribed procedure to locate a short to supply, and test the module driver only after wiring and sensors are ruled out.

Common fixes

• Repair a pinched F reference wire that is touching a supply source.
• Clean or replace corroded or loose connector terminals and secure the connection.
• Repair damaged circuit F wiring or a confirmed short to supply.
• Clear codes after repair and perform any vehicle-required reset or relearn.

Can I keep driving?

Avoid driving if the engine runs poorly, enters limp mode, or has starting trouble because the high F reference can affect several sensors. If operation is normal, limit driving and arrange diagnosis soon to reduce the risk of worsening faults or a no-start.