Powertrain, generic (extended)

P23F5 Cylinder 4 Injector B Air-Fuel Ratio Imbalance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P23F5 concerns cylinder 4, the end cylinder of a four-cylinder engine. Many four-cylinder units now carry two injectors per cylinder: Toyota's 8AR-FTS turbo (D-4ST) and its Dynamic Force engines such as the M20A (D-4S), Hyundai's Smartstream G2.5 GDi and T-GDi, and the updated Ford 2.3 EcoBoost of the 2024 Mustang. With a single bank, all cylinders share one wide-band sensor ahead of the catalyst; GM, for example, rates imbalance from how strongly that signal varies from one firing event to the next. No manufacturer links P23F5 to a vehicle in public papers. If P2BF0 or P2BF1 (Fuel Control System B lean or rich) appear as well, the whole port-fuel path is off rather than one injector. P219F and P21D2 cover the same cylinder.

Likely causes

Deposits or wear in injector B of cylinder 4

Air leak at the intake runner of cylinder 4

Low-pressure (port) fuel rail problem showing first at cylinder 4 (look for P2BF0/P2BF1)

Symptoms

Check engine light on
Slight vibration at idle
Fuel trim shifted on the single bank

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€80–800

Time0.5–4 h

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

Parts involved

fuel injector b cyl 4

References: law.cornell.edu, en.wikipedia.org, en.wikipedia.org, en.wikipedia.org.