P23FA: Cylinder 9 Injector B Air-Fuel Ratio Imbalance

P23FA concerns cylinder 9, which among passenger-car engines fitted with dual injection realistically means a V10. The best-known example is the 5.2 litre V10 of the Lamborghini Huracán, described as the first V10 to combine direct and multi-point injection. Its firing order 1-6-5-10-2-7-3-8-4-9 alternates between cylinders 1 to 5 and 6 to 10, so cylinder 9 belongs to the second group and fires last. Five cylinders feed each exhaust sensor here, so the share of one faulty cylinder in the measured signal is small; CARB therefore permits a bank-wide or misfire entry if the method cannot isolate the cylinder. No manufacturer publishes P23FA, and NHTSA's bulletin index holds no entry for it. Check P21A4, P0309 and the circuit code P21D7.

High severity. Can I keep driving?Avoid driving if the light is flashing or the engine is shaking: unburned gasoline can damage the catalytic converter.

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

Symptoms

Check engine light on
Little or no effect on the high-revving engine's behaviour
Bank trim of the second cylinder group shifted

Most likely causes

Multi-point (port) injector of cylinder 9 deviating
Leak in the intake path of cylinder 9
Valve seat or compression problem on cylinder 9

What to check, in order

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

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

Good to know

It affects emissions.

What each character of P23FA means

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

Frequently asked questions

Can I keep driving with code P23FA?

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

What causes code P23FA?

The most common causes are: multi-point (port) injector of cylinder 9 deviating; leak in the intake path of cylinder 9; valve seat or compression problem on cylinder 9.

Related codes

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.