Powertrain, generic (extended)

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

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

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.

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

Symptoms

Check engine light on
Rough idle, possibly misfire on cylinder 10
Higher fuel consumption or exhaust smell

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€0–1,500

Time0.5–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injector cyl 10intake manifoldcylinder compression

References: law.cornell.edu, static.nhtsa.gov.