Leaking or sticking fuel injector on bank 2; Faulty mass air flow sensor over-reporting airflow, causing excess fuel delivery; Leaking evaporative emissions purge valve allowing fuel vapor into the intake; High fuel pressure from a failed fuel pressure regulator or restricted return line; Contaminated engine oil with fuel dilution affecting crankcase ventilation; Worn spark plugs or ignition misfire on bank 2 leaving unburned fuel in the exhaust; Leaking intake manifold gasket or vacuum line causing unmetered air that the ECU misinterprets

DTC codes / Volkswagen codes / P1139

P1139 · VolkswagenLong Term Fuel Trim Add Fuel Bank 2 System Too Rich

Q: What does code P1139 mean?

Long Term Fuel Trim Add Fuel Bank 2 System Too Rich. P1139 on Volkswagen vehicles means the engine control module has detected that the long-term fuel trim on bank 2 has reached its rich limit, so the computer is being forced to remove fuel to compensate for an excessively rich mixture. Bank 2 is running too rich and the ECU can no longer correct it within its normal adjustment range.

P1139 on Volkswagen vehicles means the engine control module has detected that the long-term fuel trim on bank 2 has reached its rich limit, so the computer is being forced to remove fuel to compensate for an excessively rich mixture. Bank 2 is running too rich and the ECU can no longer correct it within its normal adjustment range.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyProfessional

AreaFuel and air metering

Symptoms you may notice

Often no symptoms besides the warning light, especially in early stages
A strong raw fuel smell from the exhaust, particularly at idle
Black sooty smoke from the tailpipe under acceleration
Noticeably worse fuel economy than usual
Rough idle or engine stumbling due to excessive fuel
Possible catalytic converter overheating and a rotten-egg sulfur smell

Common causes, most likely first

Leaking or sticking fuel injector on bank 2
Faulty mass air flow sensor over-reporting airflow, causing excess fuel delivery
Leaking evaporative emissions purge valve allowing fuel vapor into the intake
High fuel pressure from a failed fuel pressure regulator or restricted return line
Contaminated engine oil with fuel dilution affecting crankcase ventilation
Worn spark plugs or ignition misfire on bank 2 leaving unburned fuel in the exhaust
Leaking intake manifold gasket or vacuum line causing unmetered air that the ECU misinterprets

How to diagnose and fix it

Connect a scan tool and record freeze-frame data and long-term fuel trim values on both banks to confirm the rich condition is isolated to bank 2
Inspect the air intake tract and vacuum lines for leaks or blockages that could skew the mass air flow sensor reading
Test the evaporative emissions purge valve for sticking open and allowing fuel vapor into the intake
Measure fuel pressure and compare with Volkswagen specifications to rule out a failing pressure regulator
Perform an injector balance test or swap bank 2 injectors to bank 1 to see if the rich trim follows the injectors
Check spark plugs and ignition coils on bank 2 for misfire evidence and replace as needed
After repairs, clear the fault memory and verify long-term fuel trim returns to near zero on a road test

Why bank 2 runs rich on Volkswagens

A leaking purge valve is one of the most commonly missed causes because it allows fuel vapor to enter the intake continuously, and the ECU sees this as an unexplained rich condition on the affected bank.
Volkswagen mass air flow sensors can drift and over-report airflow without setting a separate code, so always compare measured airflow against expected values before condemning injectors.
Fuel dilution in the engine oil from repeated short trips can raise crankcase vapor hydrocarbon content and skew fuel trim, so check oil condition and smell as part of the diagnosis.
This code does not always mean the catalytic converter is failing; a rich condition can damage the converter over time, but replacing it without fixing the root cause will lead to a repeat failure.
On some Volkswagen engines, a leaking intake manifold gasket can cause unmetered air that the ECU compensates for by adding fuel, and the resulting trim can appear rich on one bank if the leak is bank-specific.

Can I keep driving with P1139?

You can drive the vehicle short distances to a repair shop, but avoid prolonged driving because the rich condition can overheat and damage the catalytic converter and dilute the engine oil. If you notice heavy black smoke or a strong fuel smell, stop driving and have the vehicle towed.

Tools that help

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