What it means
The control module detected that cylinder 12 is not contributing to engine power as expected. Possible causes include an injector, compression, or other cylinder-specific problem.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The control module compares cylinder 12’s contribution to engine output with the other cylinders, using engine-speed changes and other operating data. It sets P0296 when cylinder 12 contributes less than expected, which can result from a fuel, ignition, compression, or cylinder-specific wiring problem.
Common causes
Most likely first.
- Injector fault on cylinder 12
- Low compression on cylinder 12
- Ignition fault on cylinder 12, if spark-ignition
- Wiring or connector fault
Symptoms
- Check-engine light
- Rough idle or engine vibration
- Misfire or hesitation
- Reduced engine power
How to diagnose it
- Read freeze-frame data and check for companion misfire or fuel-system codes to see when cylinder 12 began contributing poorly.
- With the engine off, inspect cylinder 12’s injector connector and wiring, and its ignition connections if the engine uses spark plugs.
- Compare cylinder 12 misfire counts or contribution data with the other cylinders at idle and under the conditions recorded in the freeze frame.
- Check the cylinder 12 injector’s electrical operation and fuel delivery using the vehicle’s specified test procedure.
- If fuel and ignition checks do not explain the imbalance, perform a compression or leak-down test on cylinder 12 and compare it with the others.
Common fixes
- Repair a loose, damaged, or corroded cylinder 12 connector or wiring.
- Repair the cylinder 12 ignition connection or replace a confirmed faulty ignition component, if spark-ignition.
- Clean or replace a confirmed restricted or faulty cylinder 12 injector.
- Repair an internal engine fault if compression testing confirms cylinder 12 is low.
Can I keep driving?
A brief, gentle trip may be possible if the engine runs smoothly, but avoid hard acceleration and stop if it shakes badly or loses power. Continued misfiring can damage the catalytic converter and worsen engine problems.
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.