P02AA: Cylinder 5 - Fuel Trim at Max Limit

What it means

Cylinder 5 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 computer adjusts fuel for cylinder 5 to keep combustion balanced. This code sets when cylinder 5's fuel-trim correction reaches its upper calibrated limit, which can happen with restricted fuel or extra air affecting that cylinder; it does not prove the cylinder itself is lean.

Common causes

Most likely first.

1. Cylinder 5 injector flow problem
2. Air leak affecting cylinder 5
3. Other cylinder-specific fuel or air imbalance

Symptoms

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

How to diagnose it

1. Review freeze-frame data and cylinder-specific fuel-trim and misfire counts to see when cylinder 5 reaches its correction limit.
2. Inspect the intake area, vacuum connections, and any seals serving cylinder 5 for leaks or damage.
3. Check cylinder 5's injector connector and wiring for loose contacts, corrosion, or damage.
4. Compare cylinder 5 injector operation and contribution with the other cylinders using suitable scan-tool or balance tests.
5. If the cause remains unclear, test fuel delivery and check cylinder 5's control circuit and mechanical condition against the manufacturer's specification.

Common fixes

• Repair an air leak affecting cylinder 5.
• Clean or replace a restricted cylinder 5 injector as indicated by testing.
• Repair cylinder 5 injector wiring or its control connection.
• Correct a cylinder-specific fuel delivery problem found during testing.

Can I keep driving?

A short, gentle drive may be possible if the engine runs smoothly, but avoid hard acceleration and long trips. If it misfires or loses power, stop driving when safe; continued misfire can damage the catalytic converter.