Vacuum leak at the intake manifold gasket or a cracked intake boot on bank 2; Failed or leaking crankcase ventilation valve or hoses on the bank 2 side; Dirty or failing mass air flow sensor reporting lower air mass than actual; Leaking intake manifold runner control flap shaft seals on older BMW six-cylinder engines; Weak or failing fuel pump delivering insufficient volume at idle; Clogged or restricted fuel injectors on bank 2 cylinders; Exhaust leak upstream of the bank 2 oxygen sensor causing a false lean reading

DTC codes / BMW codes / P1165

P1165 · BMWFuel Trim Adaptation Additive Per Ignition Bank 2 High

Q: What does code P1165 mean?

Fuel Trim Adaptation Additive Per Ignition Bank 2 High. P1165 on BMW vehicles means the engine computer has detected that the additive fuel trim adaptation for bank 2 has exceeded its high limit, indicating a persistent lean condition that the system can no longer correct. The additive trim affects fuel delivery at idle and low load, so the computer is adding extra fuel beyond its normal range on the bank that contains cylinders 2 through 4 on most BMW inline-six engines.

P1165 on BMW vehicles means the engine computer has detected that the additive fuel trim adaptation for bank 2 has exceeded its high limit, indicating a persistent lean condition that the system can no longer correct. The additive trim affects fuel delivery at idle and low load, so the computer is adding extra fuel beyond its normal range on the bank that contains cylinders 2 through 4 on most BMW inline-six engines.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Rough or unstable idle, sometimes with a slight shake felt through the chassis
Occasional hesitation or stumble when accelerating from a stop
Slightly higher fuel consumption than usual
In rare cases, a lean misfire code or reduced engine power message may accompany the light

Common causes, most likely first

Vacuum leak at the intake manifold gasket or a cracked intake boot on bank 2
Failed or leaking crankcase ventilation valve or hoses on the bank 2 side
Dirty or failing mass air flow sensor reporting lower air mass than actual
Leaking intake manifold runner control flap shaft seals on older BMW six-cylinder engines
Weak or failing fuel pump delivering insufficient volume at idle
Clogged or restricted fuel injectors on bank 2 cylinders
Exhaust leak upstream of the bank 2 oxygen sensor causing a false lean reading

How to diagnose and fix it

Use a scan tool to read live fuel trim data and confirm bank 2 additive trim is above the high limit while bank 1 remains normal
Perform a smoke test on the intake system to locate vacuum leaks on the bank 2 side, including the intake boot and manifold gasket
Inspect and test the crankcase ventilation valve and hoses for cracks or internal failure
Clean or replace the mass air flow sensor if its reported air mass is lower than expected for the engine speed and load
Check fuel pressure and volume at idle to rule out a weak fuel pump or clogged fuel filter
Test the bank 2 oxygen sensor response and inspect for exhaust leaks upstream of the sensor
After repairs, clear adaptations and drive the vehicle through a complete warm-up cycle to verify the additive trim returns to a normal range

Why bank 2 additive trim is not always a vacuum leak

A failing mass air flow sensor can cause additive trim to go high on one bank only because the sensor sits upstream of the split, and the computer may attribute the lean condition to the bank with the most sensitive oxygen sensor response.
On BMW inline-six engines, the crankcase ventilation valve is a common culprit that many technicians overlook because it is hidden under the intake manifold and its failure often does not produce a whistle or visible smoke.
The additive trim specifically affects idle and low-load fuel delivery, so a code P1165 with normal long-term multiplicative trim points to a small leak that only matters at idle rather than a major intake system failure.
A leaking exhaust gasket or cracked exhaust manifold before the bank 2 oxygen sensor can pull in outside air and make the sensor report a false lean condition, causing the computer to add fuel when the mixture is actually correct.
Do not replace the bank 2 oxygen sensor based on this code alone, because a sensor that is slow or biased will usually set a separate oxygen sensor code rather than pushing additive trim to its limit.

Can I keep driving with P1165?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or sustained high-speed driving because the lean condition on bank 2 can raise combustion temperatures and stress the catalytic converter. If the engine runs rough or misfires, stop driving and arrange a tow.

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.