Short to earth in the wiring of one of the sensors on the shared reference C feed; Faulty sensor internally pulling the shared reference voltage down (for example a pressure, position or pedal sensor); Chafed, pinched or water-damaged wiring harness shorting the reference line to earth or another circuit; Corroded or damaged connector terminals or water ingress at a sensor plug; Low or unstable battery or supply voltage, or poor ECU earth connections; Internal fault in the engine control unit reference voltage regulator.

P0698

Sensor Reference Voltage C Circuit Low.

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
98: FaultThe specific fault in that area

What it means

P0698 means the engine control unit has detected that the 'C' sensor reference (supply) voltage circuit is below its expected range, normally a 5 volt or similar feed shared by several sensors. Which sensors share reference C depends on the vehicle, so the wiring diagram is essential. The code sets when the monitored supply voltage falls too low for longer than the calibrated time.

Symptoms

Engine warning light on
Poor running, hesitation or reduced power
Limp mode or restricted throttle response
Erratic or missing readings from several sensors at once
Rough idle or stalling
Possible hard starting or no start

Possible causes

Short to earth in the wiring of one of the sensors on the shared reference C feedlikely
Faulty sensor internally pulling the shared reference voltage down (for example a pressure, position or pedal sensor)likely
Chafed, pinched or water-damaged wiring harness shorting the reference line to earth or another circuitpossible
Corroded or damaged connector terminals or water ingress at a sensor plugpossible
Low or unstable battery or supply voltage, or poor ECU earth connectionspossible
Internal fault in the engine control unit reference voltage regulatorrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting other sensor circuit codes that point to a shared feed
Check battery condition and charging voltage, and inspect the main earths and ECU earth connections
Use the vehicle wiring diagram to identify which sensors share reference C on this model and engine
Inspect the harness and connectors of those sensors for chafing, corrosion, moisture or pushed-back pins
With the ignition on, measure the reference voltage at the ECU or a sensor connector and compare it with the specified value
Unplug the sensors on the shared circuit one at a time and watch whether the reference voltage recovers, which identifies the faulty sensor or branch
Test the reference wire for continuity to earth with the ECU and sensors disconnected
If wiring and sensors test good, check the ECU power supplies and earths before suspecting the control unit

How to fix

Replace the sensor that is pulling the reference voltage down
Repair or replace the shorted or damaged section of wiring
Clean, repair or replace corroded or damaged connectors and terminals
Correct battery, charging or earth faults
Repair or replace the engine control unit only after all external causes are ruled out, with any coding it requires

Can I keep driving?

Medium severity

The car may run in a reduced-power mode and could stall or become unpredictable, so avoid long journeys and get it checked soon. If it stalls, loses power badly or drives erratically, stop driving until it is repaired.

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