P02A6: Cylinder 4 - Fuel Trim at Max Limit

What it means

Cylinder 4 fuel trim has reached its maximum calibrated limit. The code indicates that the control module cannot apply the required correction; it does not by itself prove the cylinder is structurally lean.

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 adjusts fueling for cylinder 4 to keep combustion within its calibrated range. P02A6 sets when the cylinder 4 fuel-trim correction reaches its maximum limit, indicating the module cannot make enough of the required adjustment; it does not alone prove the cylinder is lean.

Common causes

Most likely first.

1. Injector restricted or clogged on cylinder 4
2. Air leak affecting cylinder 4
3. Low fuel pressure or delivery problem
4. Cylinder 4 sensor, wiring, or control fault

Symptoms

• Check-engine light
• Rough idle or engine vibration
• Misfire or hesitation
• Reduced engine power

How to diagnose it

1. Record freeze-frame data and compare live cylinder 4 misfire and fuel-trim readings at idle and under the conditions that set the code.
2. Inspect cylinder 4’s intake area for a local air leak and check its injector connector and wiring for damage.
3. Check for other fuel or air-metering codes that could point to a broader delivery or measurement problem.
4. Test fuel pressure and delivery against the manufacturer’s specification to rule out a supply problem affecting the engine.
5. Check cylinder 4 injector flow and relevant sensor or control-circuit operation using the maker’s approved procedures.

Common fixes

• Repair an air leak affecting cylinder 4.
• Repair damaged wiring or a poor connection at cylinder 4’s injector or related circuit.
• Clean or replace a restricted cylinder 4 injector if flow testing confirms it.
• Correct a fuel-pressure or delivery fault to the manufacturer’s specification.
• Repair a sensor or control fault only after circuit testing identifies it.

Can I keep driving?

Limit driving if the engine misfires, hesitates, or loses power; avoid heavy loads and hard acceleration. A persistent misfire can damage the catalytic converter, and the underlying fault can worsen.