What it means
Ignition L Control Signal Circuit High: the signal voltage is above the expected range. This line drives an ignition coil group; a fault causes misfire on those cylinders.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The ignition L control circuit carries the module’s command for a group of ignition coils. P03FF sets when the module detects voltage above the expected range on that circuit, which can interfere with spark control and cause misfires in the cylinders served by the L group.
Common causes
Most likely first.
- Short to B+
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Engine misfire or rough running
- Hesitation or reduced power
- Possible hard starting or no-start
How to diagnose it
- Save freeze-frame data and check misfire counts to identify when the high signal appears and which cylinders are affected.
- With the ignition off, inspect the L control wire and connectors for damage, corrosion, loose pins, or contact with a battery-positive feed.
- Check whether voltage on the L circuit exceeds the expected range under the conditions recorded in the freeze frame.
- With power isolated as specified by the manufacturer, test the L wire for a short to battery positive and examine pinched sections.
- If the harness passes, test the coil group and module driver according to the manufacturer's procedure.
Common fixes
- Repair an L wire pinched against a power feed.
- Clean or repair corroded, loose, or damaged connector terminals.
- Repair a confirmed short to battery positive in the L circuit.
- Replace a failed coil-group component or module driver only after testing confirms the fault.
Can I keep driving?
If the engine is misfiring or losing power, avoid hard acceleration and long trips because unburned fuel can damage the catalytic converter. Stop if it runs severely rough or is hard to keep running.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.