Open or damaged wire in the ignition coil control circuit between the ECM and the coil; Shorted ignition coil primary winding or internal coil driver; Corroded, loose, or backed-out terminal at the coil or ECM connector; Short to voltage on the control circuit from chafed wiring or water intrusion; Failed ignition coil driver inside the ECM (less common but possible); Aftermarket alarm or remote start wiring tapped into the ignition circuit

DTC codes / P03xx · Ignition system and misfire / P03FF

P03FFIgnition L Control Signal Circuit High

Q: What does code P03FF mean?

Ignition L Control Signal Circuit High. P03FF means the engine control module (ECM) has detected a high-voltage condition on the ignition coil control circuit for a coil the manufacturer labels 'L'. The ECM commands the coil to fire by pulling that circuit low, and it monitors the circuit for an unexpected high voltage that indicates an open circuit, a short to voltage, or a failed coil driver.

P03FF means the engine control module (ECM) has detected a high-voltage condition on the ignition coil control circuit for a coil the manufacturer labels 'L'. The ECM commands the coil to fire by pulling that circuit low, and it monitors the circuit for an unexpected high voltage that indicates an open circuit, a short to voltage, or a failed coil driver.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Rough idle or a noticeable misfire under load
Reduced engine power or a limp-home mode on some vehicles
Slight hesitation or stumble during acceleration
Poor fuel economy if the affected cylinder is misfiring
In rare cases, a no-start condition if multiple ignition circuits are affected

Common causes, most likely first

Open or damaged wire in the ignition coil control circuit between the ECM and the coil
Shorted ignition coil primary winding or internal coil driver
Corroded, loose, or backed-out terminal at the coil or ECM connector
Short to voltage on the control circuit from chafed wiring or water intrusion
Failed ignition coil driver inside the ECM (less common but possible)
Aftermarket alarm or remote start wiring tapped into the ignition circuit

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm when the high-voltage condition was set
Inspect the ignition coil connector and the ECM connector for corrosion, loose pins, or pushed-out terminals
Measure resistance of the ignition coil primary and secondary windings and compare with the manufacturer's specification
Back-probe the control circuit at the coil and check for a short to voltage with the key on and the ECM disconnected
Perform a wiggle test on the harness while watching a multimeter or oscilloscope on the control circuit
If the circuit and coil test good, substitute a known-good coil and clear the code to see if it returns
If the code persists with a verified-good circuit and coil, diagnose the ECM driver circuit or replace the ECM as a last resort

What the high-voltage reading really means

A high-voltage code on an ignition control circuit often means the circuit is open, not that the coil is receiving too much voltage, so a simple coil swap can miss a broken wire.
The ECM monitors the control circuit with the key on and the engine off, so a code can set before the engine ever cranks and may not produce a drivability symptom.
Water intrusion into the coil-on-plug valley or a cracked coil boot can corrode the control terminal and set this code without any visible misfire.
Aftermarket remote start or alarm installers sometimes tap the ignition coil control wire, creating a high-resistance or shorted connection that sets P03FF intermittently.
A failed ECM driver for one coil is rare, but it is the correct diagnosis only after the harness and coil have been proven good under load and vibration.

Can I keep driving with P03FF?

You can usually drive the vehicle to a repair shop if the only symptom is the warning light, but avoid heavy acceleration and long trips because a misfiring cylinder can overheat the catalytic converter. If the engine is running rough or lacks power, keep driving to a minimum and have it diagnosed promptly.

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.