P029E

Cylinder 2 - Fuel Trim at Max Limit

P029E is a generic OBD-II powertrain diagnostic trouble code: Cylinder 2 - Fuel Trim at Max Limit. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P029E
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P029E means

Code P029E is stored when the powertrain control module (PCM) detects that the individual fuel trim correction applied to cylinder 2 has reached the maximum allowable positive limit — typically around +25% — and still cannot achieve the target air-fuel ratio. Unlike global fuel trim codes, per-cylinder fuel trim monitoring uses crankshaft and camshaft position data cross-referenced with exhaust oxygen sensor readings to isolate which cylinder is running lean. A maximum trim limit means the ECM is commanding the injector to deliver as much additional fuel as the strategy permits, yet exhaust feedback confirms the mixture remains too lean for that cylinder. Sustained operation in this state causes the cylinder to run hotter than normal, raising the risk of pre-ignition, detonation, and eventual piston or valve damage. On diesel engines (EDC17, MD1, MG1 families), this often manifests as a cylinder balance deviation exceeding the calibrated threshold. Prompt diagnosis is essential because prolonged lean operation can cause irreversible mechanical damage and will worsen fuel economy and emissions simultaneously.

Common causes

Most-frequently reported root causes when P029E is logged.

  • 1
    Clogged or restricted fuel injector on cylinder 2 limiting fuel delivery
  • 2
    Low fuel pressure from a failing fuel pump or blocked fuel filter
  • 3
    Vacuum leak near cylinder 2 intake port or intake manifold gasket allowing unmetered air
  • 4
    Faulty or contaminated oxygen / lambda sensor providing incorrect lean feedback
  • 5
    MAF or MAP sensor malfunction causing the ECM to underestimate air mass
  • 6
    EGR valve stuck open introducing excessive exhaust gas into the intake
  • 7
    Faulty fuel pressure regulator causing insufficient rail pressure

Symptoms drivers notice

MIL (Check Engine Light) illuminated, possibly flashing during hard acceleration
Rough or uneven idle with a noticeable single-cylinder miss on cylinder 2
Reduced power output and hesitation under load
Poor fuel economy as the ECM attempts to compensate with extra fueling on other cylinders
Possible misfire codes (P030X) stored alongside P029E
Delayed cold-start or hard-start complaints

How to diagnose P029E

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record live fuel trim data per cylinder; confirm cylinder 2 LTFT is pegged at maximum while others are within ±10%
  2. 2
    Perform an injector balance or cylinder contribution test to verify cylinder 2 is delivering less fuel than adjacent cylinders
  3. 3
    Inspect cylinder 2 injector for clogging using a noid light and flow test; clean or replace if restricted
  4. 4
    Check fuel rail pressure with a gauge to rule out pump or regulator fault
  5. 5
    Smoke-test the intake manifold and vacuum lines around cylinder 2 for unmetered air leaks
  6. 6
    Test the oxygen sensor(s) for response time and correct voltage swing; replace if sluggish or stuck
  7. 7
    Verify MAF sensor reading against known-good values at idle and 2500 RPM; clean or replace if out of range

Related powertrain codes

Frequently asked questions

Can I drive with P029E active?

Short distances at light load are possible, but continued driving risks detonation and piston damage from sustained lean combustion in cylinder 2. Have it diagnosed promptly.

Why is only one cylinder affected if the fuel pump is weak?

A weak pump usually raises fuel trim on all cylinders. Cylinder-specific trim at max limit more commonly points to a single faulty injector or a localised vacuum leak near that cylinder's intake port.

Will cleaning the injector fix it?

Ultrasonic or on-car injector cleaning resolves restriction caused by deposit build-up in many cases. If the injector coil or needle is mechanically damaged, cleaning will not suffice and replacement is required.

Does P029E affect emissions test results?

Yes. A lean cylinder raises NOx emissions and may prevent catalyst light-off on that bank, causing a failure on tailpipe emissions or an automatic fail due to the stored MIL.

Disabling P029E in software

RaceTune can permanently disable P029E — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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