What it means
The primary control circuit of ignition coil A reads a voltage above the expected level — typically an open primary circuit or a short to battery voltage on the primary control wire. The ECU sees no normal current flow, coil A does not fire, and the cylinder misfires. Causes: an open or disconnected primary wire, an internal open in the coil, or a faulty ECU 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 uses its primary circuit to build the charge that produces spark at its assigned plug. The engine control module monitors the coil A control circuit and sets this code when its signal is higher than expected, often because the circuit is open or shorted to battery voltage.
Common causes
Most likely first.
- Primary wire shorted to battery
- Open primary winding
- 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
- Save freeze-frame data and review live misfire counts to identify when the cylinder served by coil A is affected.
- Inspect coil A's connector and primary wire for a disconnected plug, broken conductor, corrosion, or damage that could leave the circuit open.
- Check the coil A connector terminals for corrosion or looseness and make sure the connector is fully seated.
- Using the wiring diagram, test the primary control wire for an open or a short to battery voltage, then test the coil winding to the manufacturer's specification.
- If the coil and wiring pass, check the ECU driver circuit using the manufacturer's diagnostic procedure.
Common fixes
- Reconnect coil A's loose connector or clean and secure its terminals.
- Repair an open primary wire or a short to battery voltage.
- Replace coil A if its primary winding is open.
- Repair the ECU driver circuit if testing confirms it is faulty.
Can I keep driving?
If the check-engine light flashes or the engine misfires heavily, stop driving when safe because continued misfiring can damage the catalytic converter. With a steady light and smooth running, keep any necessary trip short and avoid hard acceleration.
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.