What it means
Ignition A 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 engine control module sends commands over the Ignition A control signal circuit to an ignition coil or coil group, as identified by the vehicle wiring. P030C sets when that circuit's signal is higher than the module expects, which can result from a short to battery voltage or a pinched wire contacting a power source.
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 or flashing
- Rough idle or engine misfire
- Hesitation or reduced power
- Engine may be difficult to start
How to diagnose it
- Check freeze-frame data and misfire counts to determine whether the cylinders served by Ignition A are affected when the code appears.
- Use the vehicle wiring diagram to locate the Ignition A signal circuit, then inspect its harness for pinching or contact with a powered wire.
- Inspect Ignition A connectors for corrosion, damaged terminals, or a displaced pin that could bridge circuits.
- Test the Ignition A signal for an unintended connection to battery voltage, following the manufacturer's isolation procedure.
- If the harness and connectors pass, test the coil group and module output against the manufacturer's procedure.
Common fixes
- Repair a pinched Ignition A signal wire contacting a power source.
- Repair damaged insulation where the Ignition A wire is shorted to battery voltage.
- Clean or replace damaged Ignition A connector terminals.
- Replace a faulty coil in the Ignition A group if testing confirms it.
- Repair or replace the control module only if its output fails the manufacturer's tests.
Can I keep driving?
If the engine misfires severely or the check-engine light flashes, stop when safe to limit catalytic-converter damage. If the light is steady and the engine runs smoothly, avoid hard acceleration and unnecessary trips until the high signal fault is repaired.
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.