Faulty ignition coil or integrated coil driver for cylinder D drawing the control signal low; Control signal wire chafed or shorted to earth between the coil connector and the control unit; Corroded, loose or damaged coil connector terminals; Water ingress or oil contamination in the coil connector or spark plug well; Missing or poor earth or supply to the coil affecting the signal reference; Fault in the engine control unit's ignition output driver.

P031E

Ignition D Control Signal Circuit Low.

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
1E: FaultThe specific fault in that area

What it means

P031E means the engine control unit has detected a low voltage on the control signal circuit for ignition coil D, which is usually the fourth coil in the firing layout, though the mapping depends on the engine. The control unit monitors the trigger signal it sends to the coil driver and saw a level lower than expected, suggesting a short to earth, a wiring fault or a failing driver or coil module.

Symptoms

Engine management light on
Misfire or rough running, especially on one cylinder
Hesitation or reduced power under load
Hard starting or extended cranking
Poor fuel economy
Engine running in a reduced-power mode

Possible causes

Faulty ignition coil or integrated coil driver for cylinder D drawing the control signal lowlikely
Control signal wire chafed or shorted to earth between the coil connector and the control unitlikely
Corroded, loose or damaged coil connector terminalslikely
Water ingress or oil contamination in the coil connector or spark plug wellpossible
Missing or poor earth or supply to the coil affecting the signal referencepossible
Fault in the engine control unit's ignition output driverrare

How to diagnose

Read all stored codes and freeze frame data, noting engine load, speed and temperature when the fault set, and check for related misfire codes.
Check which cylinder is coil D on this engine using the manufacturer's firing order and coil layout, as the labelling varies by model.
Inspect the coil connector, wiring and harness routing for chafing, heat damage, corrosion, moisture or oil contamination.
Clear the code and see if it returns immediately, or only when the engine is hot, wet or under load.
Swap coil D with a known good coil from another cylinder and see whether the fault or misfire follows the coil.
With the connector unplugged, check the coil supply voltage and earth, and test the control signal wire for continuity and for a short to earth against the wiring diagram.
Check the spark plug for the affected cylinder for wear, fouling or incorrect gap, as it can stress the coil.
If wiring and coil are good, check the control unit's output with a scope or breakout lead and follow the manufacturer's procedure.

How to fix

Replace the faulty ignition coil, fitting new spark plugs if they are worn or fouled.
Repair or replace the damaged control signal wiring section, using proper soldered and sealed joints.
Clean or replace corroded connector terminals or the whole connector, and seal against moisture.
Restore the coil supply or earth connection if found faulty.
Rectify any oil or water leak into the spark plug wells, such as a leaking valve cover gasket or plug tube seal.
Repair or replace the control unit only after all wiring and coil faults are ruled out, and follow the manufacturer's procedure.

Can I keep driving?

Medium severity

Short, gentle journeys are usually possible, but a misfiring cylinder can overheat and damage the catalytic converter and washes oil from the bore. Have it fixed soon and avoid heavy loads, and stop driving if the engine light flashes.

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