Fuel Trim Malfunction (Bank 2)
P0173 — Fuel Trim Malfunction (Bank 2). It is a high-severity fault: you should avoid long trips until it's fixed. The most common cause is vacuum leak (intake manifold, brake booster hose, pcv line) — lean condition undetectable by o2 sensor,faulty oxygen sensor bank 2 — unable to report air-fuel ratio accurately,fuel pressure regulator failure — insufficient or excessive fuel pressure,fuel pump deterioration — low fuel volume or pressure at idle and load,dirty fuel injectors — uneven fuel spray pattern or flow restriction,maf sensor contamination — incorrect air mass reading triggers rich correction. Typical fix: replace downstream oxygen sensor (o2 sensor bank 2).
"Pull over and deal with this. The light isn't bluffing."
P0173 is a powertrain diagnostic trouble code. It identifies a fault related to OBD II fault code P0173 is defined as “Fuel Trim Malfunction (Bank 2)”, and is set either when the PCM (Powertrain Control Module) experiences difficulty in controlling/maintaining the ideal air/fuel mixture, or receives a fuel trim request from the post-catalytic oxygen sensor that exceeds the PCM’s ability to adjust the fuel trim to meet the requested level of adjustment over a specified period of time. Bank 2 refers to the bank of cylinders that does not contain cylinder #1. The powertrain control module monitors this circuit or component continuously and sets P0173 when the signal or value is outside the expected range, implausible or missing. This can affect engine performance, fuel economy or emissions and usually turns on the check-engine light. The base function may still work, but performance can be affected, so the fault should be diagnosed. Diagnosis generally means inspecting the related wiring, connectors and power/ground references, then verifying the component against specification with a scan tool.
- MIL illuminated — verify with: OBD2 scanner (freeze frame data),Engine running lean or rich — verify with: test drive, monitor fuel trim live data,Rough idle or hesitation under load — verify with: RPM stability observation,Poor fuel economy — verify with: fuel consumption log over 100+ miles,Engine may run normally despite fault code — verify with: extended test drive
| # | Cause |
|---|---|
| 01 | Vacuum leak (intake manifold, brake booster hose, PCV line) — lean condition undetectable by O2 sensor,Faulty oxygen sensor Bank 2 — unable to report air-fuel ratio accurately,Fuel pressure regulator failure — insufficient or excessive fuel pressure,Fuel pump deterioration — low fuel volume or pressure at idle and load,Dirty fuel injectors — uneven fuel spray pattern or flow restriction,MAF sensor contamination — incorrect air mass reading triggers rich correction |
Typical operations: O2 Sensor - Upstream, Mass Air Flow Sensor · avg labour ≈ 0.6 h.
| Workshop labour by country | Hourly rate | Est. labour |
|---|---|---|
| IT | €45/h | €28–€540 |
| ES | €55/h | €35–€660 |
| FR | €75/h | €47–€900 |
| UK | £80/h | £50–£960 |
| DE | €95/h | €60–€1140 |
| US | $120/h | $76–$1440 |
| Parts & total | DIY | Pro |
|---|---|---|
| Fuel Trim Malfunction (Bank 2) | €40–150 | €150–400 |
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A Honda Civic owner reported to NHTSA: “VEHICLE STARTED MAKING A WHINING NOISE AND EVENTUALLY WOULD NOT ACCELERATE. VEHICLE COASTED TO A STOP ON THE SIDE OF THE ROAD WHERE IT HAD TO BE TOWED. IT WAS CHECKED BY COMPUTER AND THE CODE P0173 CAME UP (TRANSMISSION FAILURE). *LA”
NO — REPAIR FIRST — get it diagnosed as soon as possible.
Typically €40–150 as a DIY repair and €150–400 at a workshop — the final figure depends on the actual cause and your vehicle.