P0174 on Mercedes-Benz: Causes, Symptoms and Fix Cost

Quick Answer

Safe to drive (short-term)

P0174 on a Mercedes-Benz means the engine is running too lean on Bank 2, the cylinder bank that does not contain cylinder 1. It appears on V6, V8 and boxer engines, and on inline-six engines whose engine management splits the cylinders into two banks with an upstream oxygen sensor each, such as BMW's M54, N52 and N54. The computer added the maximum extra fuel it can (long-term fuel trim past roughly +25 percent) but still measured too much air against the ideal 14.7:1 ratio. The most common cause is an unmetered air leak: a cracked vacuum hose or leaking gasket. The cheapest fixes, a MAF clean or a split vacuum hose, can cost under 100 euros; a gasket or PCV repair runs roughly 40 to 260 euros.

Severity: Moderate · Fuel System
Typical repair cost, all makes: €30-€700

Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Mercedes-Benz and Skanyx tells you what P0174 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.

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What does P0174 mean on a Mercedes-Benz?

The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0174.

Mercedes-Benz C-Class

2005-2024

Four-cylinder C-Class models are single-bank and report P0171; the V6 and V8 variants (M272, M276 and the AMG V8) can set P0174. On the M272 and M276 V6 the intake manifold air-flow control runner and its seals are a known vacuum-leak point on Bank 2, and the crankcase breather (oil separator) diaphragm tears with age, leaning out the mixture.

What causes P0174 on a Mercedes-Benz?

Beyond the generic causes listed on the main P0174 page, these are the patterns noted for Mercedes-Benz models:

Intake manifold runner or flap seal vacuum leak on the M272 and M276 V6
: Mercedes-Benz C-Class
Crankcase breather oil-separator diaphragm tear leaning Bank 2
: Mercedes-Benz C-Class

How to diagnose P0174 on a Mercedes-Benz with OBD2

Follow these steps to pinpoint the root cause of P0174:

Check whether P0171 is also stored. Both codes together points to a whole-engine cause (dirty MAF, low fuel pressure, or a large central vacuum leak), not a Bank 2-specific fault, so start there
Read short-term and long-term fuel trims on Bank 2 with a scan tool. A long-term trim sustained above about +10 percent shows the bank is correcting for a lean mixture, and the code typically sets near the ECU's limit of around +25 percent; trims that worsen at idle suggest a vacuum leak, trims that worsen under load suggest a fuel-delivery problem
Smoke-test the intake, or spray a small amount of carburettor cleaner around the Bank 2 intake manifold gaskets, vacuum hoses, and PCV connections, watching for an RPM change that pinpoints the leak
Inspect and clean the MAF sensor with dedicated MAF cleaner, then recheck trims; a clogged sensor element is a frequent and cheap fix
Check fuel pressure at the rail with a gauge and compare against the manufacturer specification, both at idle and under a snap-throttle load
Inspect for an exhaust leak ahead of the Bank 2 upstream O2 sensor and verify the sensor is switching correctly before condemning any parts
Compare Bank 1 and Bank 2 trims side by side - a large gap between the two banks isolates the problem to Bank 2 hardware rather than a shared cause

How much does P0174 cost to fix on a Mercedes-Benz? (EUR)

Estimated repair costs for P0174 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Fix vacuum leak (replace hose or gasket)	€5–€60	€60–€200	€65–€260	Moderate
Clean or replace MAF sensor	€10–€200	€20–€60	€30–€260	Easy
Replace PCV valve	€10–€80	€30–€120	€40–€200	Easy
Replace fuel pump	€100–€400	€100–€300	€200–€700	Professional
Clean fuel injectors	€15–€50	€50–€150	€65–€200	Moderate

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

These codes are often seen alongside P0174 or point to related issues, on any make:

Looking for the full P0174 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0174 guide

Diagnose P0174 on your Mercedes-Benz

Your car logged P0174. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €30-€700 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.