These codes belong to an individual-cylinder fuel correction: a diesel's cylinder balance control measures each cylinder's crankshaft acceleration and adjusts its injection quantity; on petrol engines a cylinder-selective mixture control does the same. CARB requires the system to report when such a correction has used up its range or one cylinder causes an imbalance. P02C9 means the module detects fuel entering cylinder 12 outside the injection pulse – the injector is leaking or dripping. A BMW patent identifies such a leak by the fact that it persists with the injector switched off. A leaking diesel injector can dilute the oil or damage the piston, so act promptly. Cylinder 12 only exists on engines with twelve or more cylinders. GM and Ford use other codes for this (P0263 ff, P219A ff); no manufacturer document describing this code with thresholds was found, so the description follows CARB and published patents.
Medium severity. Can I keep driving?Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.
Cylinder 12 is numbered according to the manufacturer: check your engine's manual before working on it.
Symptoms
- Check engine light on
- Rough idle, vibration
- Smoke, fuel smell, knocking
Most likely causes
- Nozzle seat or needle of the cylinder 12 injector leaking
- Deposits keeping the needle from closing fully
- Rail pressure too high
- Wrong or wrongly coded injector
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P02C9 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 2: Fuel injection
- C9: Specific fault in that system
Frequently asked questions
Can I keep driving with code P02C9?
Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.
What causes code P02C9?
The most common causes are: nozzle seat or needle of the cylinder 12 injector leaking; deposits keeping the needle from closing fully; rail pressure too high.
Related codes
- P02C6Cylinder 12 - Fuel Trim at Max Limit
- P02C7Cylinder 12 - Fuel Trim at Min Limit
- P02C8Cylinder 12 - Injector Restricted
- P0296Cylinder 12 Contribution/Balance
- P232DCylinder 12 Fuel Injector A Offset Learning At Min Limit
- P0172System Too Rich Bank 1
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.