Faulty ignition coil or coil-on-plug assembly for cylinder D; Damaged or corroded wiring harness or connector at the ignition coil; Open circuit in the ignition control signal wire between the PCM and coil; Failed ignition control module (if equipped separately); Loose or damaged PCM connector or internal PCM driver fault; Aftermarket alarm or remote start wiring interfering with ignition circuits

DTC codes / P03xx · Ignition system and misfire / P031D

P031DIgnition D Control Signal Circuit/Open

Q: What does code P031D mean?

Ignition D Control Signal Circuit/Open. P031D indicates that the powertrain control module (PCM) has detected an open circuit or abnormal condition on the ignition control signal circuit for cylinder D, which is typically the fourth cylinder in the engine's firing order. The PCM commands a spark event but does not see the expected electrical response from the ignition coil or ignition control module, so it sets this code and may illuminate the check engine light.

P031D indicates that the powertrain control module (PCM) has detected an open circuit or abnormal condition on the ignition control signal circuit for cylinder D, which is typically the fourth cylinder in the engine's firing order. The PCM commands a spark event but does not see the expected electrical response from the ignition coil or ignition control module, so it sets this code and may illuminate the check engine light.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Check engine light illuminated, often with no other noticeable symptoms
Engine misfire or rough running, especially under acceleration or load
Reduced engine power or limp mode in some vehicles
Shaking or vibration felt through the steering wheel or seat
Difficulty starting or intermittent stalling
Poor fuel economy or increased emissions

Common causes, most likely first

Faulty ignition coil or coil-on-plug assembly for cylinder D
Damaged or corroded wiring harness or connector at the ignition coil
Open circuit in the ignition control signal wire between the PCM and coil
Failed ignition control module (if equipped separately)
Loose or damaged PCM connector or internal PCM driver fault
Aftermarket alarm or remote start wiring interfering with ignition circuits

How to diagnose and fix it

Perform a visual inspection of the ignition coil, connector, and wiring for cylinder D, looking for corrosion, chafing, or loose pins
Use a scan tool to check for pending or stored misfire codes and freeze-frame data to confirm the fault is consistent
Swap the ignition coil from cylinder D with a known-good coil from another cylinder and see if the code moves, confirming a faulty coil
Measure resistance of the ignition control signal wire from the PCM to the coil connector to check for an open circuit
Check for power and ground at the ignition coil connector with the key on and during cranking
Inspect and test the PCM connector and, if necessary, perform a wiggle test on the harness while monitoring live data
Replace the faulty ignition coil, repair wiring, or reprogram/replace the PCM as diagnosed

What a P031D often hides

A loose or corroded connector at the ignition coil is a frequent cause that can mimic a failed coil, so always inspect the pins before replacing parts.
The code may set intermittently due to vibration or heat, and a coil that tests good when cold can still fail when hot, so perform tests both cold and at operating temperature.
Aftermarket remote start or alarm systems spliced into ignition wiring often create open circuits or interference that triggers this code.
On some engines, a failed spark plug or excessive gap can stress the ignition coil and cause the PCM to detect an open control circuit, so inspect plugs as well.
The PCM driver for the ignition coil can fail internally, but this is rare; confirm wiring and coil integrity before condemning the PCM.

Can I keep driving with P031D?

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

Tools that help

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