P21C0 applies only to twelve-cylinder engines (V12 or W12), since passenger-car engines with exactly eleven cylinders do not exist. Examples with direct injection are BMW's N74 twin-turbo V12, found in the BMW 760i and in Rolls-Royce models such as Ghost, Wraith and Dawn, and the 6.3-litre W12 FSI. The code would report that cylinder 11 missed its cold-start injection timing, for instance when the extra injection for catalyst heating is shifted. Whether BMW, Rolls-Royce or Audi use P21C0 is not documented publicly. The legal basis is CARB's demand for separate cold-start diagnostics, allowing the module to tell such faults apart from warm-running timing faults (P021E). Related: P0211 (injector circuit), P0311 (misfire).
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 11 is numbered according to the manufacturer: check your engine's manual before working on it.
Symptoms
- Check engine light after cold starts
- Barely noticeable on the road; a twelve-cylinder engine masks a single cylinder well
Most likely causes
- Direct injector of cylinder 11 with changed opening behaviour
- Heat-damaged wiring or connector at injector 11
- Injector driver for cylinder 11 in the engine control module faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- It affects emissions.
What each character of P21C0 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 1: Air and fuel
- C0: Specific fault in that system
Frequently asked questions
Can I keep driving with code P21C0?
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 P21C0?
The most common causes are: direct injector of cylinder 11 with changed opening behaviour; heat-damaged wiring or connector at injector 11; injector driver for cylinder 11 in the engine control module faulty.
Related codes
- P21BFCold Start Cylinder 10 Injection Timing
- P21C1Cold Start Cylinder 12 Injection Timing
- P021ECylinder 11 Injection Timing
- P0211Cylinder 11 Injector A Circuit/Open
- P0311Cylinder 11 Misfire Detected
- P05ECCold Start Injection Timing Performance
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.