Fuel and air

P029A — Cylinder 1 Fuel Trim at Maximum Limit

Severity: medium Drive with care, to a shop

What P029A means

The engine control module continually adjusts fuel delivery for each cylinder based on mixture feedback from its sensors. P029A is set when the correction for cylinder 1 reaches its maximum allowed limit and the module can no longer compensate. That cylinder is running noticeably too lean or too rich.

Symptoms

  • Check Engine light on
  • Rough idle
  • Hesitation when accelerating
  • Reduced power
  • Higher fuel consumption
  • Possible misfire

Possible causes

  1. Faulty or clogged cylinder 1 fuel injector
  2. Vacuum or intake air leak near cylinder 1
  3. Inaccurate oxygen sensor readings
  4. Faulty MAF or MAP sensor
  5. Low fuel pressure (weak pump, clogged filter)
  6. Damaged injector wiring or connector
  7. Exhaust leak ahead of the oxygen sensor

How to diagnose

  1. Read codes and freeze frame data, and note whether trim is positive or negative
  2. Review short- and long-term fuel trims at idle and under load
  3. Inspect the intake, hoses and manifold gasket for leaks, using a smoke machine if possible
  4. Check the cylinder 1 injector connector, wiring, resistance and control signal
  5. Compare cylinder balance with an injector balance test or by checking for misfires
  6. Measure fuel pressure against specification
  7. Check MAF, MAP and oxygen sensor readings
  8. Inspect the exhaust for leaks

Common fixes

  • Clean or replace the cylinder 1 injector
  • Repair intake or vacuum leaks
  • Replace a faulty MAF, MAP or oxygen sensor
  • Replace the fuel filter or pump if pressure is low
  • Repair the injector wiring or connector

Questions and answers

What does P029A mean?

The engine computer has used up all its ability to adjust fuel for cylinder 1. This points to a lasting mixture imbalance in that cylinder.

Can I drive with P029A?

Briefly, yes, but don't put off the repair. Running on a wrong mixture for long can cause misfires and damage the catalytic converter.

Where should I start diagnosing P029A?

Start with the fuel trim values and a check for air leaks, then test the cylinder 1 injector and fuel pressure.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.