What it means
The primary control circuit of ignition coil A reads a voltage below the expected level — usually a short to ground on the primary driver wire or a low-resistance fault in the coil primary winding. Coil A cannot build a normal charge, so the cylinder it fires misfires, especially under load. Causes: short to ground in the primary wiring, an internal coil primary fault, or a faulty ECU/igniter driver.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Ignition coil A charges from the primary circuit, then releases high voltage to fire its assigned spark plug. The engine control module monitors coil A's primary control signal and sets this code when it detects a low circuit level, which can result from a short to ground or an internally shorted coil winding.
Common causes
Most likely first.
- Internal coil short
- Primary wire shorted to ground
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light on, possibly flashing
- Engine misfire or rough idle
- Hesitation under acceleration
- Reduced power
How to diagnose it
- Record freeze-frame data and check live misfire counts to see when the cylinder served by coil A begins misfiring.
- Inspect coil A's connector and primary wiring for corrosion, damaged insulation, loose pins, or contact with ground.
- Check whether the coil A connector and terminals are fully seated and clean, since corrosion or poor contact can disrupt the control circuit.
- With the wiring diagram, test coil A's primary control wire for a short to ground and check the winding as specified by the manufacturer.
- If the coil and wiring pass, have the control signal and ECU driver checked using the manufacturer's diagnostic procedure.
Common fixes
- Clean and secure corroded or loose coil A connector terminals.
- Repair primary wiring shorted to ground.
- Replace coil A if its primary winding fails testing.
- Repair the ECU driver circuit if testing confirms it is faulty.
Can I keep driving?
A flashing check-engine light or a strong misfire means stop driving as soon as it is safe; unburned fuel can damage the catalytic converter. If the light is steady and the engine runs smoothly, limit driving and avoid hard acceleration until diagnosed.
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.