Open or damaged wire in the ignition control circuit for cylinder C; Corroded or loose electrical connector at the ignition coil or module; Failed ignition coil or ignition control module for that cylinder; Faulty powertrain control module driver circuit (rare); Poor ground connection affecting the ignition system; Aftermarket alarm or remote start wiring interfering with the ignition circuit

DTC codes / P03xx · Ignition system and misfire / P031A

P031AIgnition C Control Signal Circuit/Open

Q: What does code P031A mean?

Ignition C Control Signal Circuit/Open. P031A indicates that the powertrain control module has detected an open circuit or abnormal condition on the ignition control signal circuit for cylinder C, meaning the coil or ignition module is not receiving the command pulse it expects. The computer monitors the control wire for voltage changes consistent with a commanded spark event and flags the code when the signal is missing, intermittent, or outside the expected range.

P031A indicates that the powertrain control module has detected an open circuit or abnormal condition on the ignition control signal circuit for cylinder C, meaning the coil or ignition module is not receiving the command pulse it expects. The computer monitors the control wire for voltage changes consistent with a commanded spark event and flags the code when the signal is missing, intermittent, or outside the expected range.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or misfire sensation, especially under load or acceleration
Hesitation or stumble during acceleration
Reduced engine power or limp mode in some vehicles
Shaking or vibration from the engine bay
Difficulty starting or extended cranking in severe cases

Common causes, most likely first

Open or damaged wire in the ignition control circuit for cylinder C
Corroded or loose electrical connector at the ignition coil or module
Failed ignition coil or ignition control module for that cylinder
Faulty powertrain control module driver circuit (rare)
Poor ground connection affecting the ignition system
Aftermarket alarm or remote start wiring interfering with the ignition circuit

How to diagnose and fix it

Inspect the ignition coil connector and wiring for corrosion, looseness, or damage
Check for continuity and resistance on the control circuit between the PCM and coil
Swap the ignition coil from cylinder C with a known-good coil to see if the misfire moves
Test the control signal with an oscilloscope or noid light to confirm the PCM is commanding spark
Repair any open or shorted wiring and replace damaged connectors
Replace the faulty ignition coil or ignition control module if the circuit tests good
Clear the code and verify the repair with a test drive and live data monitoring

What the code does not always mean

A P031A does not automatically condemn the ignition coil; a chafed wire or corroded pin in the connector is just as common and far cheaper to fix.
Some vehicles set this code from a momentary glitch caused by a low battery or poor ground, so clearing the code and seeing if it returns is a valid first step.
Aftermarket remote starters or alarm systems spliced into ignition wiring frequently cause open-circuit codes that look like component failures.
The PCM driver circuit can fail, but it is rare; always rule out the coil and wiring before suspecting the computer.
A misfire from a bad spark plug or fuel injector can sometimes trigger a control circuit code as the PCM sees abnormal feedback, so do not overlook secondary ignition components.

Can I keep driving with P031A?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because a persistent misfire can overheat the catalytic converter. If the engine is running very rough or flashing the check engine light, stop driving and have it towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.