Powertrain, generic (extended)

P231F Cylinder 12 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P231F closes the balance-limit series at cylinder 12, the last cylinder of a twelve-cylinder engine. It says the balancing routine has used up the fuel trim for that cylinder without matching it to the rest. Public manufacturer documentation is missing, and the NHTSA index contains no bulletin naming it. CARB's monitor requirement, and its demand that the stored code identify the cylinder wherever the method allows, apply to these rare engines as well. A V12 has two independent banks, so compare the matching bank code (P219A or P219B) with the misfire counter P0312 and with P21A7 before fitting parts. Mercedes' bulletins for its four-cylinders, where worn valve seats caused balancing faults, are a reminder that the injector is not always the culprit.

Likely causes

Injector of cylinder 12 delivering too much or too little (deposits, wear)
Air leak at the intake port or injector seal of cylinder 12
Valve of cylinder 12 not sealing (worn seat or guide), low compression
Poor contact at the connector of injector 12

Symptoms

  • Check engine light on
  • Rough idle, possibly misfire on cylinder 12
  • 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 12intake manifoldcylinder compression

Related codes

P21A7P231EP0312P0212P219AP219B

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