Vacuum leak on bank 2, such as a cracked intake boot, leaking intake manifold gasket, or deteriorated vacuum hose.; Faulty crankcase ventilation (CVV) valve or associated hoses on bank 2, allowing unmetered air into the intake.; Contaminated or failing mass air flow (MAF) sensor, causing incorrect air mass readings that affect both banks but may trigger bank 2 first.; Leaking fuel injector or incorrect fuel pressure on bank 2, though less common than vacuum leaks.; Worn or dirty throttle body causing inconsistent idle air flow.; Exhaust leak upstream of the oxygen sensor on bank 2, leading to false lean readings.; Faulty oxygen sensor on bank 2, providing inaccurate feedback to the ECM.

DTC codes / BMW codes / P1175

P1175 · BMWFuel Trim Adaptation Additive Bank 2 Malfunction

Q: What does code P1175 mean?

Fuel Trim Adaptation Additive Bank 2 Malfunction. P1175 on BMW vehicles indicates that the engine control module (ECM) has detected an out-of-range additive fuel trim adaptation value for bank 2, meaning the ECM can no longer correct the air-fuel mixture at idle using its long-term additive adjustment. The additive trim specifically compensates for small, consistent vacuum leaks or fuel delivery errors that affect idle quality, and when the adaptation hits its limit, the ECM stores this fault.

P1175 on BMW vehicles indicates that the engine control module (ECM) has detected an out-of-range additive fuel trim adaptation value for bank 2, meaning the ECM can no longer correct the air-fuel mixture at idle using its long-term additive adjustment. The additive trim specifically compensates for small, consistent vacuum leaks or fuel delivery errors that affect idle quality, and when the adaptation hits its limit, the ECM stores this fault.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
Rough or unstable idle, sometimes accompanied by slight shaking.
Occasional engine stumble or hesitation when coming to a stop.
Slightly elevated or fluctuating idle speed.
Poor fuel economy in some cases, though less common with additive trim faults.
Failed emissions test due to incorrect idle mixture.

Common causes, most likely first

Vacuum leak on bank 2, such as a cracked intake boot, leaking intake manifold gasket, or deteriorated vacuum hose.
Faulty crankcase ventilation (CVV) valve or associated hoses on bank 2, allowing unmetered air into the intake.
Contaminated or failing mass air flow (MAF) sensor, causing incorrect air mass readings that affect both banks but may trigger bank 2 first.
Leaking fuel injector or incorrect fuel pressure on bank 2, though less common than vacuum leaks.
Worn or dirty throttle body causing inconsistent idle air flow.
Exhaust leak upstream of the oxygen sensor on bank 2, leading to false lean readings.
Faulty oxygen sensor on bank 2, providing inaccurate feedback to the ECM.

How to diagnose and fix it

Perform a visual inspection of all intake and vacuum lines on bank 2 for cracks, loose connections, or deterioration.
Use a smoke machine to detect vacuum leaks in the intake system, including the intake manifold gasket and CVV hoses.
Check the crankcase ventilation valve and hoses for proper operation and leaks.
Clean the mass air flow sensor with approved cleaner and verify its readings with a scan tool.
Test fuel pressure and inspect injectors for leaks or clogging on bank 2.
Inspect the throttle body for carbon buildup and clean if necessary, then perform a throttle adaptation reset.
Check for exhaust leaks before the bank 2 oxygen sensor and replace the sensor if faulty.

Additive Trim Faults Often Point to Vacuum Leaks

Additive fuel trim specifically affects idle mixture, so a P1175 is most likely caused by a vacuum leak that is present at idle but may seal under load.
A faulty crankcase ventilation valve is a common culprit on BMW engines and can cause additive trim faults without obvious driveability symptoms.
The mass air flow sensor may be contaminated with oil from an over-oiled aftermarket air filter, leading to skewed readings that affect bank 2 more than bank 1.
Do not replace the oxygen sensor or catalytic converter based solely on this code; always verify the additive trim values with a scan tool and check for unmetered air first.
Bank 2 additive trim faults can sometimes be caused by a leaking intake manifold gasket that only leaks when the engine is cold, so a smoke test on a cold engine is advisable.

Can I keep driving with P1175?

You can generally continue driving with P1175, but avoid prolonged idling and heavy loads until the fault is repaired, as the engine may run rough and fuel economy may suffer. Have the vehicle diagnosed soon to prevent potential damage to the catalytic converter from an overly rich or lean condition.

Tools that help

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