What it means
The ignition C control signal circuit is open — typically the PCM drive line for the first ignition coil group has lost continuity.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The powertrain controller sends an ignition control signal on circuit C to operate the associated ignition hardware. P031A indicates that the controller detects an open or loss of continuity in that signal circuit, which can prevent the affected ignition components from firing correctly.
Common causes
Most likely first.
- Open wire between PCM and coil
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
Symptoms
- Rough running or misfire
- Hard starting or no start
- Reduced engine power
How to diagnose it
- Read freeze-frame data and related ignition or misfire codes to identify when the circuit C fault occurred and which engine conditions were affected.
- Use the vehicle’s wiring information to identify ignition control circuit C and inspect its connectors and harness for disconnection, backed-out pins, or visible damage.
- With the ignition off as specified by the service information, check circuit C wiring continuity and look for an open between the controller and the ignition component.
- Check connector pin fit and inspect the relevant ignition component connection before testing the circuit under the manufacturer’s specified conditions.
- If the wiring and connections pass, follow the vehicle’s procedure to test the ignition driver and controller rather than replacing the module based on the code alone.
Common fixes
- Seat a loose connector or backed-out pin in ignition control circuit C.
- Repair an open or damaged wire in circuit C.
- Replace a faulty ignition component if its control connection or internal circuit fails testing.
- Repair or replace a control module only if vehicle-specific testing confirms its circuit C driver is faulty.
Can I keep driving?
If the engine is misfiring or the check engine light flashes, stop driving when safe because unburned fuel can damage the catalytic converter. If it starts and runs smoothly with a steady light, limit driving and arrange prompt diagnosis; a worsening open circuit can cause more severe misfire or a no-start.
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.