The Quick Answer above is the generic definition. What follows is the model-specific detail for the BMW models that log P0151.
DTC/P0151·BMW
P0151 on BMW: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)BMW
P0151 on a BMW means the upstream oxygen sensor on bank 2 has reported a low voltage for too long, which reads as too much oxygen in the exhaust, a lean mixture. Bank 2 is the half of a V6, V8 or flat-six engine that does not contain cylinder 1 (a few inline-sixes with a split exhaust, such as BMW's M54, also have one). It is the same fault as P0131 on the other bank. The cause is either a real lean condition on that bank, such as a vacuum or exhaust leak, or a sensor or wiring fault that makes the signal read low.
Typical repair cost, all makes€45 - €320
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BMW 5 Series (545i/540i/550i)
2003-2010The N62 V8 in the 545i, 540i and 550i has a pre-cat sensor for each bank: bank 1 covers cylinders 1-4 and bank 2 cylinders 5-8. BMW's N62 service training describes broadband (wide-range) sensors ahead of the catalytic converters, so on live data compare the bank 2 lambda reading with bank 1 instead of looking for a 0.1-0.9 V switching signal. For the 550i, BMW parts listings give the bank 1 and bank 2 pre-cat sensors different part numbers, so order the one specified for bank 2. Fuel trims raised on bank 2 only suggest a real lean condition on that side rather than a failed sensor.
BMW 3 Series (E46 325i/330i)
2000-2006The M54 in the 325i and 330i is an inline-six, but its exhaust is split in two: BMW's training material describes catalytic converters built into the exhaust manifolds, with a narrowband (Bosch LSH 25) pre-cat sensor on top of each manifold, and the MS43 engine management runs a separate mixture control for each half. Cylinders 1-3 are bank 1 and cylinders 4-6 are bank 2, and BMW parts listings name the bank 2 pre-cat sensor as the one for cylinders 4-6, so a bank 2 code on this car is genuine and points at the pre-cat sensor for the rear three cylinders. A P0151 with P0174 on this engine means cylinders 4-6 are reading lean, so check the intake side for unmetered air as well as the sensor.
What causes P0151 on a BMW?
Beyond the generic causes listed on the main P0151 page, these are the patterns noted for BMW models:
BMW 5 Series (545i/540i/550i)Air leak affecting the bank 2 cylinders of the N62 V8
BMW 5 Series (545i/540i/550i)Ageing bank 2 pre-cat sensor reading low
BMW 3 Series (E46 325i/330i)Unmetered air reaching cylinders 4-6 on the M54
BMW 3 Series (E46 325i/330i)Ageing pre-cat sensor for cylinders 4-6 reading low
How to diagnose P0151 on a BMW with OBD2
Follow these steps to pinpoint the root cause of P0151:
- Read all stored codes and freeze frame data. P0174 alongside P0151 points to a real lean condition on bank 2. P0171 and P0174 together point to something both banks share, such as the MAF sensor, fuel pressure or a large intake leak
- Warm the engine and compare Bank 2 Sensor 1 with Bank 1 Sensor 1 on live data. A narrowband sensor stuck below about 0.2 volts while the bank 1 sensor keeps switching points at bank 2
- Check short- and long-term fuel trims for each bank. High positive trims on bank 2 only mean the engine computer is adding fuel to that bank, which supports a real lean condition rather than a sensor fault
- Smoke-test the intake. Look for leaks at the intake manifold gaskets, vacuum hoses and crankcase breather on the bank 2 side
- Inspect the exhaust between the bank 2 cylinder head and the sensor for leaks, cracks or a loose flange
- Inspect the bank 2 sensor wiring and connector for chafing against the exhaust or body that could short the signal to ground
- If trims are normal and no leaks are found, replace the bank 2 upstream sensor, clear the code and confirm it stays off after a drive cycle
How much does P0151 cost to fix on a BMW? (EUR)
Estimated repair costs for P0151 in EUR, compiled across makes. Expect BMW parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Codes related to P0151
These codes are often seen alongside P0151 or point to related issues, on any make:
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See the main P0151 guideSkanyx · BMW
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