Damaged, corroded or loose connector at the ignition coil for output C; Open circuit or high resistance in the control signal wire between the coil and the control unit; Faulty ignition coil or integrated coil driver for output C; Missing or poor power or earth supply to the coil; Wiring chafed or damaged by heat, vibration or previous repairs; Fault in the control unit's ignition output driver.

P031A

Ignition C Control Signal Circuit/Open.

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
1A: FaultThe specific fault in that area

What it means

P031A means the engine control unit has detected an open circuit on the control signal line for ignition output C. The control unit monitors the ignition driver circuit to the coil, or to the coil's built-in driver, and sets the code when the signal is missing or does not respond as commanded. Which cylinder 'C' refers to depends on the engine and firing order, so check the vehicle-specific data.

Symptoms

Engine misfire, especially under load
Rough idle or hesitation
Illuminated or flashing engine warning light
Reduced power or the engine running in a limited mode
Hard starting or a long crank
Poor fuel economy

Possible causes

Damaged, corroded or loose connector at the ignition coil for output Clikely
Open circuit or high resistance in the control signal wire between the coil and the control unitlikely
Faulty ignition coil or integrated coil driver for output Clikely
Missing or poor power or earth supply to the coilpossible
Wiring chafed or damaged by heat, vibration or previous repairspossible
Fault in the control unit's ignition output driverrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note any misfire codes that appear with P031A.
Check the vehicle-specific information to identify which coil and cylinder is ignition output C on this engine.
Inspect the coil connector and wiring for damage, corrosion, bent or pushed-back pins, and signs of heat or chafing.
Check the coil's power and earth supplies with the ignition on, following the manufacturer's wiring diagram.
Test the control signal wire for continuity back to the control unit, and check for a short to earth or to voltage.
Swap the suspect coil with a known good one from another cylinder, clear the codes and see whether the fault follows the coil.
Use a scan tool to check live misfire counters, and a scope to check the control signal if one is available.
If the wiring and coil are proven good, check the control unit connector and consult the manufacturer's data on the control unit.

How to fix

Repair or replace damaged wiring, and clean or replace corroded connector terminals.
Replace the faulty ignition coil for output C, and check the spark plugs in that cylinder at the same time.
Restore the correct power or earth supply to the coil by repairing the supply wiring or connections.
Re-pin or replace the connector if the terminals are loose or the pins damaged.
Repair or replace the control unit only after the wiring and coil have been fully ruled out.
Clear the codes after the repair and road test to confirm the fault does not return.

Can I keep driving?

Medium severity

Short, gentle journeys are possible, but a misfiring cylinder can overheat the catalytic converter and make the engine run roughly. Get it fixed soon, and stop driving if the warning light flashes or the engine misfires badly.

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