P0173 on BMW: Causes, Symptoms and Fix Cost
Quick Answer
Safe to drive (short-term)
P0173 on a BMW means the ECU has pushed long-term fuel trim on Bank 2 to the limit of its correction range and still cannot maintain the target air-fuel ratio. Because P0173 only affects one bank, it usually points to something specific to Bank 2 (a leak, a degraded sensor, or a dirty injector on that bank) rather than a whole-engine issue like a clogged fuel filter that would affect both banks.
- Severity
- Moderate · Fuel System
- Typical repair cost, all makes
- €70-€420
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your BMW and Skanyx tells you what P0173 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0173 mean on a BMW?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the BMW models that log P0173.
BMW 3 Series
2006-2024
No 3 Series has been built with a V6, and the only V8 is the S65 in the 2008-2013 M3 (E90, E92, E93), a port-injected engine. The N52 and N54 inline-sixes (and the older M54) still report fuel trim in two banks: each group of three cylinders has its own upstream oxygen sensor, and cylinders 1-3 are bank 1, cylinders 4-6 bank 2. So P0173 can appear on these engines, and a bank-2-only fault points to cylinders 4-6: their upstream sensor, injectors, or an intake or exhaust leak on that half.
Source: ge39.com, bimmerworld.com, bimmerworld.com, en.wikipedia.org, en.wikipedia.org
Sources
- ge39.com ge39.com/files/m54x5.pdf
- bimmerworld.com bimmerworld.com/Exhaust/O2-Sensors/BMW-Engine-Oxygen-Sensor-O2-11787545074.html
- bimmerworld.com bimmerworld.com/Exhaust/O2-Sensors/BMW-Engine-Oxygen-Sensor-O2-11787545075.html
- en.wikipedia.org en.wikipedia.org/wiki/BMW_S65
- en.wikipedia.org en.wikipedia.org/wiki/BMW_3_Series_(E90)
What causes P0173 on a BMW?
Beyond the generic causes listed on the main P0173 page, these are the patterns noted for BMW models:
Bank 2 (cylinders 4-6) upstream oxygen sensor ageing on the N52 and N54
: BMW 3 Series
Intake or exhaust leak affecting cylinders 4-6
: BMW 3 Series
How to diagnose P0173 on a BMW with OBD2
- Read live data: focus on short-term and long-term fuel trim for Bank 2. A long-term trim above +20% or below -20% confirms the bank has been hitting its limits
- Compare Bank 2 trims to Bank 1. If only Bank 2 is out of range, the cause is bank-specific (one injector, one sensor, one manifold gasket section)
- Smoke-test the intake on Bank 2 specifically. On V engines, intake manifold gaskets fail one side at a time as plastic shrinks unevenly
- Swap the upstream sensors between banks and re-check live data. If the high trim follows the sensor, replace it; if it stays on the original bank, focus on mechanical causes
- Inspect for exhaust leaks ahead of the Bank 2 upstream sensor. A small leak can pull fresh air into the exhaust stream and trick the sensor into reading lean
How much does P0173 cost to fix on a BMW? (EUR)
Estimated repair costs for P0173 in EUR, compiled across makes. Expect BMW parts and labour towards the upper end of each range.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Fix vacuum leak on Bank 2 | €10–€80 | €60–€200 | €70–€280 | Moderate |
| Replace Bank 2 upstream O2 or air-fuel ratio sensor | €60–€200 | €60–€150 | €120–€350 | Moderate |
| Clean fuel injectors on Bank 2 | €30–€120 | €100–€300 | €130–€420 | Professional |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Codes related to P0173
These codes are often seen alongside P0173 or point to related issues, on any make:
Looking for the full P0173 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0173 guide