What it means
Cylinder 12 fuel trim deviates significantly from the bank average — a single-cylinder injector or intake 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 cylinder 12's contribution to the air-fuel correction for its bank with the other cylinders on that bank. This code sets when cylinder 12's fuel-trim contribution differs substantially from the bank average, which can result from fuel delivery, air leakage, ignition, or compression problems.
Common causes
Most likely first.
- Clogged or leaking cylinder 12 injector
- Cylinder 12 intake leak or airflow issue
- Cylinder 12 ignition misfire
- Low compression in cylinder 12
Symptoms
- Check-engine light
- Rough idle or engine vibration
- Engine hesitation or reduced power
- Increased fuel consumption
How to diagnose it
- Check freeze-frame data and live fuel-trim and misfire counts to see when cylinder 12's imbalance occurs and whether it is isolated.
- Inspect cylinder 12's injector connector, wiring, intake runner, and nearby hoses for looseness, damage, or signs of leakage.
- Check for an intake leak at cylinder 12 and compare its injector operation with the other cylinders using the vehicle's approved test method.
- Inspect cylinder 12's ignition components and check for a cylinder-specific misfire before attributing the imbalance to fuel delivery.
- If those checks do not identify the fault, perform a compression or leak-down test on cylinder 12 and compare results with the manufacturer's specification.
Common fixes
- Repair a loose or damaged cylinder 12 injector connector or wiring.
- Repair a leak at the cylinder 12 intake runner or its connected hose.
- Clean or replace a restricted or leaking cylinder 12 injector as testing indicates.
- Repair the cylinder 12 ignition fault or address low compression if confirmed.
Can I keep driving?
If the engine runs smoothly and the warning is steady, limit driving and arrange diagnosis soon; avoid hard acceleration. If it runs roughly, loses power, or the check-engine light flashes, stop driving when safe because continued misfire can damage the catalytic converter.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.