P231D: Cylinder 10 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance

P231D is the cylinder 10 code of the balance-limit series. On a V10 it marks the last cylinder, on a V12 one of the inner ones; smaller engines cannot set it. The individual fuel correction for cylinder 10 has reached its end stop while the controller tried to equalise the mixture. No maker publishes a description, and no NHTSA bulletin lists it. The principle is the one Mercedes describes on its M260/M264 four-cylinders as injector quantity adjustment for cylinder balancing, with P1CEF85 when it nears the upper limit, there often caused by worn valve seats. CARB's imbalance monitor (13 CCR 1968.2 (e)(6.2.1)(C)) applies to these engines too. Look at injector 10, the intake runner seal and valve tightness, and check whether P0310 or P21A5 are stored as well.

Cylinder 10 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 10
• Higher fuel consumption or exhaust smell

Most likely causes

• Injector of cylinder 10 delivering too much or too little (deposits, wear)
• Air leak at the intake port or injector seal of cylinder 10
• Valve of cylinder 10 not sealing (worn seat or guide), low compression
• Poor contact at the connector of injector 10

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 P231D means

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

Frequently asked questions

Can I keep driving with code P231D?

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

What causes code P231D?

The most common causes are: injector of cylinder 10 delivering too much or too little (deposits, wear); air leak at the intake port or injector seal of cylinder 10; valve of cylinder 10 not sealing (worn seat or guide), low compression.

Related codes

• P21A5Cylinder 10 Air-Fuel Ratio Imbalance
• P231CCylinder 9 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance
• P231ECylinder 11 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance
• P0310Cylinder 10 Misfire Detected
• P0210Cylinder 10 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 11028267 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.