Faulty ignition coil or integrated coil driver for circuit C; Damaged, corroded or loose connector at the coil C; Control signal wire shorted to voltage, or open circuit giving a high reading; Poor or missing coil power or earth supply affecting the driver circuit; Separate ignition module or driver stage fault, on engines that use one; Internal fault in the engine control unit driver.

P031C

Ignition C Control Signal Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
1C: FaultThe specific fault in that area

What it means

P031C means the engine control unit has detected a high voltage fault on the control signal circuit for ignition 'C'. The control unit monitors the signal it sends to the coil or ignition driver, and it saw a level higher than expected. Which cylinder 'C' refers to depends on the engine and its firing layout, so confirm this from the wiring diagram for your model.

Symptoms

Engine management warning light on
Misfire or rough running, especially under load
Hesitation or poor acceleration
Hard starting or intermittent no-start
Reduced fuel economy
Engine running in a reduced-power mode

Possible causes

Faulty ignition coil or integrated coil driver for circuit Clikely
Damaged, corroded or loose connector at the coil Clikely
Control signal wire shorted to voltage, or open circuit giving a high readingpossible
Poor or missing coil power or earth supply affecting the driver circuitpossible
Separate ignition module or driver stage fault, on engines that use onepossible
Internal fault in the engine control unit driverrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine load, speed and temperature when the fault set. Look for other ignition or misfire codes.
Identify which coil or ignition channel is 'C' from the wiring diagram for the specific model and engine.
Visually inspect the coil connector, wiring and nearby loom for heat damage, chafing, oil contamination, water ingress and corrosion.
Check the coil's power supply and earth connections with a multimeter, including voltage drop under load.
Swap the suspect coil with a known good one on another cylinder and see whether the fault or misfire follows it.
Back-probe the control signal wire with the ignition on and check its voltage against the manufacturer's specification. With the control unit connector disconnected, check the wire for a short to voltage and for continuity.
Check the spark plug condition and gap for the affected cylinder, as worn plugs can stress the coil.
If the wiring and coil test good, check the engine control unit for software updates and test its driver output with an oscilloscope before condemning the unit.

How to fix

Replace the faulty ignition coil or ignition driver module.
Repair or replace damaged wiring, terminals or connectors in the control signal circuit.
Restore a good power supply or earth connection to the coil.
Fit new spark plugs of the correct specification if they are worn or damaged.
Update the engine control unit software if the manufacturer lists it as a fix, or repair or replace the control unit if its driver has failed.

Can I keep driving?

Medium severity

Short, gentle journeys are usually possible, but avoid heavy loads and high revs. A misfire can damage the catalytic converter, so have it fixed soon, and stop driving if the engine is misfiring badly or the warning light is flashing.

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