P23FC: Cylinder 11 Injector B Air-Fuel Ratio Imbalance

P23FC is reserved for cylinder 11, so it can only belong to twelve-cylinder engines that add an extra injector in every cylinder. Such a pairing is hard to find in public engine data. Volkswagen's W12 illustrates the point: its early versions used twelve injectors in the intake manifold, one per cylinder, while the 6.3 FSI of the Audi A8 L W12 switched to direct injection with six-hole high-pressure injectors, again one per cylinder. Neither layout has an injector B. Any twelve-cylinder engine built with dual injection would still fall under CARB's imbalance rule, including the expectation that the code names the cylinder to the extent the detection strategy permits. No manufacturer documents P23FC. Should it appear, compare P21A6, P0311 and the circuit code P21D9 before replacing anything.

Cylinder 11 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

• Check engine light on
• Hardly any change in smoothness on a twelve-cylinder engine

Most likely causes

• Second injector of cylinder 11 delivering a wrong quantity
• Intake leak at cylinder 11
• Code read from an engine that has no injector B (scan tool or software issue)

What to check, in order

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

1. See whether the light is flashing: if so, reduce engine load and avoid driving
2. Inspect the spark plugs, coils, and connectors
3. Swap the coil with another cylinder and see if the misfire moves with it
4. Check the injector and look for air leaks
5. Run a compression test if everything above checks out

Good to know

• It affects emissions.

What each character of P23FC means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 3: Ignition and misfires
• FC: Specific fault in that system

Frequently asked questions

Can I keep driving with code P23FC?

Avoid driving if the light is flashing or the engine is shaking: unburned gasoline can damage the catalytic converter.

What causes code P23FC?

The most common causes are: second injector of cylinder 11 delivering a wrong quantity; intake leak at cylinder 11; code read from an engine that has no injector B (scan tool or software issue).

Related codes

• P21A6Cylinder 11 Air-Fuel Ratio Imbalance
• P21D9Cylinder 11 Injector B Circuit/Open
• P0311Cylinder 11 Misfire Detected
• P23FBCylinder 10 Injector B Air-Fuel Ratio Imbalance
• P23FDCylinder 12 Injector B Air-Fuel Ratio Imbalance
• P23FEBank 1 System B Air-Fuel Ratio Imbalance
• P23FFBank 2 System B Air-Fuel Ratio Imbalance

Sources

• law.cornell.edu: 13 CCR 1968.2
• en.wikipedia.org: Volkswagen Group 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.