P23FD: Cylinder 12 Injector B Air-Fuel Ratio Imbalance

What it means

The control module detects an air-fuel ratio imbalance associated with injector B for cylinder 12. The code identifies an imbalance, but does not by itself establish that the injector has a particular fault.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control module compares combustion and mixture feedback for cylinder 12 with the other cylinders to detect an imbalance associated with injector B. The code points to cylinder 12 and injector B, but does not prove that the injector itself is faulty.

Common causes

Most likely first.

1. Injector B flow or delivery fault
2. Injector B circuit or wiring fault
3. Other cylinder-specific air or fuel imbalance

Symptoms

• Check-engine light on
• Rough idle or engine vibration
• Reduced power
• Increased fuel consumption

How to diagnose it

1. Record freeze-frame data and compare cylinder-specific misfire or fuel-balance data to see when cylinder 12 began differing from the others.
2. Inspect injector B at cylinder 12 and its connector and wiring for damage, loose pins, corrosion, or fuel leakage.
3. Check for intake leaks or other air and fuel problems that could affect cylinder 12 before replacing the injector.
4. Use scan-tool output controls, if supported, to compare injector B's response with the other injectors.
5. Test injector B's circuit and delivery against the manufacturer's specification, then investigate other cylinder-specific causes if both check out.

Common fixes

• Repair damaged wiring or secure and clean the injector B connector at cylinder 12.
• Correct a cylinder 12 intake leak or other identified air or fuel imbalance.
• Repair the injector B control circuit if testing finds an electrical fault.
• Clean or replace injector B at cylinder 12 if testing confirms poor delivery.

Can I keep driving?

If the engine runs smoothly and the warning light is steady, limit driving and arrange diagnosis soon; avoid heavy acceleration. Rough running or a flashing warning light can indicate damaging misfires, so stop driving and have the vehicle checked.