Leaking or stuck-open fuel injector on cylinder 5 delivering too much fuel; Faulty or contaminated mass airflow sensor over-reporting airflow and skewing fuel delivery; Leaking intake manifold gasket or vacuum line near cylinder 5 that the computer misreads as extra air; Worn or fouled spark plug on cylinder 5 causing incomplete combustion that the oxygen sensor reads as rich; Failed ignition coil or plug wire on cylinder 5 producing a misfire that drives fuel trim to its limit; Exhaust leak before the oxygen sensor or a lazy upstream oxygen sensor giving a false rich signal; Mechanical fault such as low compression or a sticking valve on cylinder 5 that upsets that cylinder's fuel trim

DTC codes / P02xx · Fuel and air metering (injector circuits) / P02AB

P02ABCylinder 5 - Fuel Trim at Min Limit

Q: What does code P02AB mean?

Cylinder 5 - Fuel Trim at Min Limit. P02AB means the engine computer has detected that the fuel trim correction for cylinder 5 has reached its minimum programmable limit, so the powertrain control module can no longer lean out that cylinder's fuel mixture any further. Cylinder 5 is running so rich that the computer has run out of authority to subtract fuel, which points to a mechanical or electrical fault rather than normal closed-loop correction.

P02AB means the engine computer has detected that the fuel trim correction for cylinder 5 has reached its minimum programmable limit, so the powertrain control module can no longer lean out that cylinder's fuel mixture any further. Cylinder 5 is running so rich that the computer has run out of authority to subtract fuel, which points to a mechanical or electrical fault rather than normal closed-loop correction.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms at first
Rough idle or a noticeable shake that is worse when the engine is cold
Black sooty exhaust smoke or a strong fuel smell from the tailpipe
Reduced fuel economy and a rich-running exhaust that can foul spark plugs
Misfire-like shudder or hesitation under light acceleration
Failed emissions test with high hydrocarbon or carbon monoxide readings

Common causes, most likely first

Leaking or stuck-open fuel injector on cylinder 5 delivering too much fuel
Faulty or contaminated mass airflow sensor over-reporting airflow and skewing fuel delivery
Leaking intake manifold gasket or vacuum line near cylinder 5 that the computer misreads as extra air
Worn or fouled spark plug on cylinder 5 causing incomplete combustion that the oxygen sensor reads as rich
Failed ignition coil or plug wire on cylinder 5 producing a misfire that drives fuel trim to its limit
Exhaust leak before the oxygen sensor or a lazy upstream oxygen sensor giving a false rich signal
Mechanical fault such as low compression or a sticking valve on cylinder 5 that upsets that cylinder's fuel trim

How to diagnose and fix it

Scan all stored and pending codes and freeze-frame data to confirm P02AB is the primary fault and not a side effect of another code
Inspect the spark plug, ignition coil and plug wire on cylinder 5 for fouling, cracks or oil contamination
Check fuel trim values for all cylinders and compare cylinder 5 against the others to see whether the fault is isolated
Test the cylinder 5 fuel injector for leakage, resistance and pulse width, and swap it with a known-good injector to see if the code moves
Smoke-test the intake manifold and vacuum lines near cylinder 5 for unmetered air leaks
Verify mass airflow sensor readings against expected values and clean or replace it only if testing proves it is out of specification
Perform a compression test and cylinder leak-down test on cylinder 5 to rule out mechanical causes before replacing electronic parts

Why cylinder 5 fuel trim hits the limit

A fuel trim at the minimum limit does not automatically mean the injector is bad; a misfiring cylinder 5 can send unburned fuel into the exhaust that the oxygen sensor reads as rich, driving the computer to pull fuel it cannot actually remove.
Technicians often replace the upstream oxygen sensor first, but a lazy sensor that reports a false rich condition will set this code without any real fuel delivery problem, so compare its signal against a known-good sensor before buying parts.
An intake vacuum leak near cylinder 5 usually causes a lean condition, but if the leak is downstream of the fuel injector and the computer has already maxed out fuel trim in the rich direction, the resulting misfire can still trigger P02AB.
Low compression on cylinder 5 from a worn ring, valve or head gasket is a commonly missed cause because the computer interprets the incomplete combustion as a rich mixture and keeps subtracting fuel until it reaches the limit.
This code is cylinder-specific, so a general rich condition from a faulty mass airflow sensor or fuel pressure regulator will usually set codes for both banks or multiple cylinders rather than isolating cylinder 5 alone.

Can I keep driving with P02AB?

You can drive cautiously to a repair shop, but avoid heavy acceleration and long trips because continued rich running on cylinder 5 can foul the spark plug, damage the catalytic converter and dilute the engine oil. If the check engine light starts flashing, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.