P231E: Cylinder 11 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance

P231E belongs to cylinder 11 and can only come from twelve-cylinder engines, V12 or W12. The per-cylinder fuel trim for cylinder 11 sits at its limit during balancing. There is no public manufacturer description and no NHTSA bulletin. On such engines six cylinders share each bank, so one deviating cylinder shifts the bank sensor signal only slightly; that is one reason CARB accepts a bank or misfire code where a single cylinder cannot be resolved. Mercedes' M177 bulletin for the cylinder 7 code of the same series shows that a software update can be the real remedy. In the workshop, compare the trim values and misfire counts of cylinder 11 (P0311, P21A6) with its neighbours before the injector is replaced.

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

Symptoms

• Check engine light on
• Rough idle, possibly misfire on cylinder 11
• Higher fuel consumption or exhaust smell

Most likely causes

• Injector of cylinder 11 delivering too much or too little (deposits, wear)
• Air leak at the intake port or injector seal of cylinder 11
• Valve of cylinder 11 not sealing (worn seat or guide), low compression
• Poor contact at the connector of injector 11

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

• Repair difficulty: medium
• It affects emissions.

What each character of P231E means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 3: Ignition and misfires
• 1E: Specific fault in that system

Frequently asked questions

Can I keep driving with code P231E?

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

What causes code P231E?

The most common causes are: injector of cylinder 11 delivering too much or too little (deposits, wear); air leak at the intake port or injector seal of cylinder 11; valve of cylinder 11 not sealing (worn seat or guide), low compression.

Related codes

• P21A6Cylinder 11 Air-Fuel Ratio Imbalance
• P231DCylinder 10 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance
• P231FCylinder 12 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance
• P0311Cylinder 11 Misfire Detected
• P0211Cylinder 11 Injector A Circuit/Open
• P219ABank 1 Air-Fuel Ratio Imbalance
• P219BBank 2 Air-Fuel Ratio Imbalance

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 10249505 0001

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.