P031B code meaning
Ignition C Control Signal Circuit Low
Powertrain system Generic code P03xx codes Check engine light
What P031B means
Ignition C is one of the control signal lines from the engine module to an ignition module, ignition output stage or group of coils; which cylinders it serves is defined by the manufacturer, not by the code standard. The code concerns the logic-level control signal, not the coil's primary current (that has its own codes, P0351 ff and P2300 ff). P031B means the control line reads low – typically shorted to ground. No manufacturer using these codes was found; GM reports coil control faults as P0351 ff (open above 30 kΩ, first trip), so the description follows CARB and that analogy. The affected coils fire wrongly or not at all, causing misfire; many modules then shut off injection to those cylinders to protect the catalyst.
P031B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P031B
- Check engine light on
- Misfire, jerking, rough idle
- Loss of power, possibly cylinders shut off
- Additional misfire codes P0300 ff
Common causes of P031B
- Most likelyControl line shorted to ground (chafing)
- PossibleInput of the ignition module or coil shorted
- PossibleMoisture or corrosion in the connector
- Less likelyDriver stage in the engine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ignition control cIgnition moduleIgnition wiring
What each part of P031B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3 | Area: ignition system or misfire. |
| 1B | The exact fault in that area. |
What to do next
- Note P031B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P031B
What does P031B mean?
P031B means "Ignition C Control Signal Circuit Low". Ignition C is one of the control signal lines from the engine module to an ignition module, ignition output stage or group of coils; which cylinders it serves is defined by the manufacturer, not by the code standard. It is a generic code, so it means the same on every make.
Is it safe to drive with P031B?
Drive gently and only to a workshop. With P031B the car can go into limp mode (reduced power) to protect itself.
Will P031B fail an emissions test?
Yes, it can. P031B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P031B to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P031B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.