P21BE: Cold Start Cylinder 9 Injection Timing

A ninth cylinder exists only on V10, V12 and W12 engines, so P21BE is limited to a handful of models. Petrol engines in this class with direct injection include the 5.2-litre V10 of Lamborghini and Audi (Huracán, R8, S6 and S8) and the 6.3-litre W12 FSI of the Audi A8, which feeds its injectors from two high-pressure pumps and two rails. Whether their engine modules use P21BE is not documented publicly, and no other manufacturer source names the code. Its meaning follows from the series: during the cold-start heating phase the injection timing of cylinder 9 deviated from its target, a fault CARB wants reported apart from warm-engine faults. There is no cold-start injection pulse code beyond cylinder 8. Related: P021C (warm), P0209, P0309.

Cylinder 9 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

• Check engine light after cold starts
• Slightly uneven idle while the engine is cold

Most likely causes

• Direct injector of cylinder 9 with deposits or slow response
• Wiring or connector fault at injector 9
• Low pressure on the rail feeding cylinder 9 (engines with two rails)

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 P21BE means

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

Frequently asked questions

Can I keep driving with code P21BE?

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 P21BE?

The most common causes are: direct injector of cylinder 9 with deposits or slow response; wiring or connector fault at injector 9; low pressure on the rail feeding cylinder 9 (engines with two rails).

Related codes

• P21BDCold Start Cylinder 8 Injection Timing
• P21BFCold Start Cylinder 10 Injection Timing
• P021CCylinder 9 Injection Timing
• P0209Cylinder 9 Injector A Circuit/Open
• P0309Cylinder 9 Misfire Detected
• P05ECCold Start Injection Timing Performance

Sources

• law.cornell.edu: 13 CCR 1968.2
• en.wikipedia.org: Lamborghini V10 engine
• 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.