P2303
Ignition Coil B Primary Control Circuit Low
Ignition / misfire
Generic OBD-II
Medium
What it means
P2303 means the ECM has detected low voltage on the primary control circuit for ignition coil B — usually a short to ground or a failing coil. That cylinder can misfire, giving a rough idle and lost power, and a sustained misfire can damage the catalytic converter, so it should not be ignored.
Medium
Can I keep driving? Drivable but expect a misfire on that cylinder — if the check-engine light flashes, drive as little as possible to protect the catalytic converter.
Common symptoms
What you'll notice
- Check-engine light on (may flash during an active misfire)
- Rough idle, stumble, or hesitation
- Loss of power on acceleration
- Slightly increased fuel consumption
Common causes
Most likely first
- Faulty ignition coil B or a short to ground in its primary windingLikely
- Wiring shorted to ground on the coil control (driver) circuitCommon
- Corroded or loose coil connectorCommon
- Chafed harness near the coilLess often
- Failed coil driver inside the ECM/ignition moduleLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and note which cylinder coil B feeds.
- Inspect the coil connector and control wire for damage or a short to ground.
- Swap coil B with a known-good coil and see if the fault follows the coil.
- Check the control wire back to the ECM for a short.
- Replace the coil if faulty, then clear and confirm the misfire is gone.
FAQ
Quick answers
Is it safe to drive with P2303?+
Only briefly. A steady misfire dumps raw fuel into the exhaust and can overheat the converter — a flashing light means stop driving soon.
Can I just clear P2303?+
It returns quickly because the ECM keeps monitoring the coil circuit until the coil or wiring is repaired.
Related codes
Often seen with P2303
Read & clear P2303 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX