P02AB

Cylinder 5 - Fuel Trim at Min Limit

P02AB is a generic OBD-II powertrain diagnostic trouble code: Cylinder 5 - Fuel Trim at Min 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
P02AB
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P02AB means

Code P02AB is stored when the powertrain control module (PCM) has driven the individual fuel trim for cylinder 5 to its minimum allowable limit in an attempt to lean out a persistently rich combustion event on that cylinder. Per-cylinder fuel trim corrections subtract fuel from the injector pulse width; when cylinder 5 continues to run rich despite maximum subtraction, the PCM can no longer correct the imbalance and sets P02AB. This code is exclusive to engines with five or more cylinders, such as inline-five (I5), inline-six (I6), V6, V8, V10, and V12 engines. The most common cause is a leaking or stuck-open fuel injector on cylinder 5 delivering more fuel than commanded. Other contributors include elevated fuel rail pressure, a saturated evaporative emissions canister purging excessive fuel vapour into the intake, or a faulty oxygen sensor reading artificially lean and driving the trim rich. Sustained over-fuelling on cylinder 5 washes the cylinder bore, dilutes crankcase oil with raw fuel, and can overwhelm the catalytic converter with unburned hydrocarbons.

Common causes

Most-frequently reported root causes when P02AB is logged.

  • 1
    Leaking or stuck-open fuel injector on cylinder 5 delivering excess fuel beyond commanded pulse width
  • 2
    Excessive fuel rail pressure caused by a faulty fuel pressure regulator holding pressure too high
  • 3
    Faulty oxygen sensor on the affected bank reading artificially lean and commanding enrichment
  • 4
    EVAP canister purge valve stuck open, flooding the intake with fuel vapour
  • 5
    Contaminated or flooded cylinder 5 from previous injector leak events requiring oil and spark plug inspection
  • 6
    Shorted injector driver circuit in the PCM holding the cylinder 5 injector energised longer than commanded
  • 7
    Coolant temperature sensor fault causing the PCM to apply cold-start enrichment when the engine is warm

Symptoms drivers notice

Illuminated MIL with per-cylinder fuel trim data showing cylinder 5 at maximum negative correction
Strong fuel odour from the exhaust or engine bay due to unburned hydrocarbons
Rough idle or engine stumble caused by over-fuelling and incomplete combustion on cylinder 5
Reduced fuel economy and elevated exhaust emissions, particularly hydrocarbons and CO
Oil level reading higher than normal or oil smelling of fuel if injector has been leaking internally
Possible black smoke from the exhaust during hard acceleration if rich condition is severe

How to diagnose P02AB

A typical diagnostic flow when this code is present.

  1. 1
    Connect an OBD-II scan tool and review live per-cylinder fuel trim data to confirm cylinder 5 is at minimum (maximum negative) trim while other cylinders are within normal range
  2. 2
    Inspect the cylinder 5 fuel injector for external leaks and perform a fuel rail pressure bleed-down test with the engine off to identify a leaking injector (pressure drops faster than normal)
  3. 3
    Perform an injector balance test to confirm cylinder 5 contributes more fuel than its neighbours
  4. 4
    Check fuel rail pressure against specification — over-pressure points to a faulty pressure regulator and enriches all injectors
  5. 5
    Inspect the EVAP purge valve for a stuck-open condition by disconnecting it and re-running the fuel trim monitor
  6. 6
    Test the oxygen sensor on the affected bank for correct voltage range and sweep speed to rule out a falsely lean sensor reading
  7. 7
    Check engine oil for fuel dilution and inspect the cylinder 5 spark plug for a wet, fuel-fouled appearance indicating chronic over-fuelling

Related powertrain codes

Frequently asked questions

Which engines can trigger P02AB?

P02AB requires a physical cylinder 5, so it only occurs in engines with five or more cylinders: inline-5 (I5), inline-6 (I6), V6, V8, V10, and V12 configurations. A standard four-cylinder engine cannot generate this code.

How does P02AB differ from P02A9 (Cylinder 4 Injector Leaking)?

P02A9 directly states that the PCM has identified a leaking injector on cylinder 4. P02AB is a fuel trim limit code — it tells you the correction has been exhausted, but the root cause still needs to be found; a leaking injector is the most common culprit, but elevated fuel pressure or EVAP faults can also be responsible.

Can P02AB damage the catalytic converter?

Yes. Excess unburned fuel exiting cylinder 5 can ignite inside the catalytic converter, generating extreme heat that melts the catalyst substrate. If P02AB is present alongside misfire codes, stop driving immediately to protect the catalytic converter.

Should I change the oil if P02AB was active for a long time?

Yes. A rich-running cylinder over-fuels the piston with raw fuel that seeps past the rings into the oil sump, diluting the lubricant and reducing its protective properties. An oil and filter change is strongly advisable after repairing the root cause.

Disabling P02AB in software

RaceTune can permanently disable P02AB — 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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