P029B: Cylinder 1 - Fuel Trim at Min Limit

What it means

Cylinder 1 fuel trim has reached its minimum calibrated limit. The code indicates that the control module cannot apply the required correction; it does not by itself prove the cylinder is structurally rich.

At a glance

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

How it works

The control module monitors fuel correction associated with cylinder 1 to keep combustion within its calibrated range. P029B sets when that correction reaches its minimum limit, so the module cannot reduce fueling enough; the code alone does not prove cylinder 1 is mechanically rich.

Common causes

Most likely first.

1. Injector leaking on cylinder 1
2. Injector stuck open or control fault
3. Excess fuel pressure
4. Cylinder 1 sensor or wiring fault

Symptoms

• Check-engine light
• Rough idle or engine vibration
• Misfire or hesitation
• Fuel odor or increased fuel consumption

How to diagnose it

1. Read freeze-frame data and cylinder 1 misfire and fuel-correction data, and check for companion injector or fuel-pressure codes.
2. Inspect cylinder 1’s injector connector and wiring for damage, shorts, or poor contact.
3. Check for signs of fuel leakage or an injector that continues to deliver fuel when it should be closed, following the manufacturer’s safety procedure.
4. Measure fuel pressure against the manufacturer’s specification and compare cylinder 1 injector operation with the other cylinders.
5. If the fuel supply and injector appear sound, check the cylinder 1 sensor inputs and control circuit using the manufacturer’s diagnostic procedure.

Common fixes

• Repair damaged or shorted cylinder 1 injector wiring or connector.
• Correct fuel pressure if testing shows it is above the manufacturer’s specification.
• Replace a confirmed leaking or stuck-open cylinder 1 injector and renew seals if required by the repair procedure.
• Repair a confirmed cylinder 1 sensor or control-circuit fault.

Can I keep driving?

If you smell fuel, the engine misfires badly, or fuel is visibly leaking, stop driving and address the fault promptly because fuel can damage the catalytic converter and presents a fire risk. Otherwise, avoid extended driving and hard acceleration until cylinder 1 fueling is checked.