Reference supply wire shorted to a higher voltage (for example a battery feed) due to chafed or damaged wiring; Damaged, corroded or water-affected connector or terminals on the shared sensor supply circuit; Faulty sensor on circuit C with an internal short pulling the supply high; Incorrect repair or aftermarket wiring work that has crossed the reference supply with another circuit; Fault inside the control module's reference voltage regulator; Outdated or faulty control module software where the manufacturer has identified it as a cause.

P0699

Sensor Reference Voltage C Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
99: FaultThe specific fault in that area

What it means

P0699 means the engine or powertrain control module has detected a voltage that is too high on the sensor reference voltage 'C' circuit, which is one of the regulated supplies (usually 5 volts) feeding a group of sensors. The module sets the code when the supply reads above its expected range, typically from a short to a higher voltage source or a fault inside the module. Which sensors share circuit C depends on the vehicle, so the wiring diagram for the specific model is needed.

Symptoms

Engine warning light on
Erratic or implausible readings from several sensors at once
Poor running, hesitation or reduced power
Engine in limp-home mode
Rough idle or stalling
Other sensor circuit codes stored alongside P0699

Possible causes

Reference supply wire shorted to a higher voltage (for example a battery feed) due to chafed or damaged wiringlikely
Damaged, corroded or water-affected connector or terminals on the shared sensor supply circuitlikely
Faulty sensor on circuit C with an internal short pulling the supply highpossible
Incorrect repair or aftermarket wiring work that has crossed the reference supply with another circuitpossible
Fault inside the control module's reference voltage regulatorrare
Outdated or faulty control module software where the manufacturer has identified it as a causerare

How to diagnose

Read all stored codes and freeze frame data, noting any other sensor circuit codes that point to the shared supply
Check the manufacturer wiring diagram to identify which sensors and connectors share reference circuit C on this model and engine
Visually inspect the wiring harness and connectors for chafing, heat damage, corrosion, water ingress and previous repairs
With the ignition on, measure the reference supply voltage at the control module or a shared sensor connector and compare it with the specified value
Unplug the sensors on circuit C one at a time while monitoring the supply voltage to see if one sensor pulls it high
With the module and sensors disconnected, test the supply wire for a short to battery voltage or to other circuits
Check the module power and earth supplies, and check for any applicable manufacturer software updates or bulletins
If wiring and sensors are proven good and the supply is still out of range, have the module assessed

How to fix

Repair or replace damaged wiring and correct any shorts to higher voltage
Clean, repair or replace faulty connectors and terminals
Replace any sensor found to be internally shorted
Correct any incorrect aftermarket or previous repair wiring
Update the control module software only where an outdated calibration is a known cause for this vehicle
Repair or replace the control module if it is confirmed faulty

Can I keep driving?

Medium severity

The car may be driveable, but poor running or limp mode is likely and the fault could worsen or affect several systems. Have it diagnosed soon and avoid long journeys or heavy loads until it is fixed.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.