P21C1: Cold Start Cylinder 12 Injection Timing

Cylinder 12 is the last cylinder of V12 and W12 engines. Direct-injection V12 include Ferrari's F140 family (FF, F12berlinetta, 812 Superfast) and BMW's N74; among W engines there is the 6.3-litre W12 FSI. P21C1 reports that during the cold-start heating phase the injection timing of cylinder 12 deviated from its target. The code closes the series P21B6–P21C1, which exists because CARB requires cold-start faults to be kept apart from normal ones; the following code, P21C2, already belongs to the SCR reductant heater. No manufacturer publishes use of P21C1. Practical cross-checks: P021F (timing, warm engine), P0212 (injector circuit) and P0312 (misfire). Repairs on these engines are workshop jobs.

Cylinder 12 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

• Check engine light after cold starts
• Hardly any drivability change, at most a slightly uneven cold idle

Most likely causes

• Injector of cylinder 12 with deposits or worn needle
• Damaged wiring at the end of the cylinder bank (injector 12)
• Cold-start calibration of the engine module out of date

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the connector and wiring of the injector indicated
2. Measure the resistance and compare it with the manufacturer's specification
3. Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
4. On diesels, check the per-cylinder injection corrections

Good to know

• It affects emissions.

What each character of P21C1 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 1: Air and fuel
• C1: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21C1?

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 P21C1?

The most common causes are: injector of cylinder 12 with deposits or worn needle; damaged wiring at the end of the cylinder bank (injector 12); cold-start calibration of the engine module out of date.

Related codes

• P21C0Cold Start Cylinder 11 Injection Timing
• P021FCylinder 12 Injection Timing
• P0212Cylinder 12 Injector A Circuit/Open
• P0312Cylinder 12 Misfire Detected
• P05ECCold Start Injection Timing Performance

Sources

• law.cornell.edu: 13 CCR 1968.2
• en.wikipedia.org: Ferrari F140 engine
• en.wikipedia.org: BMW N74
• en.wikipedia.org: Volkswagen W12 engine

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.