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Known Faults Database

Mercedes-Benz B-Class Common Problems & Known Faults (UK)

If you are considering buying a used Mercedes-Benz B-Class, there are several major reliability issues worth knowing about first. Our garage database tracks 3 known faults for this model, 2 of them rated high severity. Every one below is a repair bill a seller has good reason not to mention.

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Mercedes-Benz B-Class W176 / W246 / C117 / X156 (continues in W177) (2012-2023) problems

Transmission/ClutchMedium severity🔧 Specialist mechanic

The 7G-DCT dual-clutch automatic suffers low-speed judder and jerky shifts as the wet clutch packs wear, and mechatronic (electrohydraulic control unit) failures that cause delayed engagement, harsh 2nd-3rd shifts, limp mode or loss of drive. Mechatronic replacement is quoted at 1200-1800 pounds by UK specialists; clutch pack replacement is similar. Neglected 40k-mile fluid changes accelerate both

Rough guide
£1200-2500

Typical symptoms

  • shuddering or juddering when pulling away from a stop
  • hesitation or a lurch when setting off, worse when cold
  • clunk into P, N or R, or harsh low-gear shifts
  • gearbox warning and limp mode in advanced cases

Affected vehicles

Engines:
All with 7G-DCT dual-clutch automatic (Getrag 724.0)
Typical mileage:
50000-100000 miles
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Mercedes-Benz B-Class W169 / W245 (2004-2012) problems

Transmission/ClutchHigh severity🔧 Specialist mechanic

The 722.8 Autotronic CVT's internal gearbox ECU fails (speed sensor circuits break down inside the sealed unit), throwing 'Transmission Visit Workshop' on the dash and dropping the car into limp mode with limited or no gear selection. A main dealer fix means a new ECU, valve body and coding at well over 1000 pounds; even specialist ECU rebuilds with fitting typically run 500-1000 pounds

Rough guide
£600-2000

Typical symptoms

  • 'Transmission Visit Workshop' warning on the dash
  • sudden limp mode or loss of drive
  • harsh or absent gear engagement, stuck in one ratio

Affected vehicles

Engines:
All with CVT automatic (722.8 Autotronic)
Typical mileage:
60000-120000 miles
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Mercedes-Benz B-Class C117 (2013-2018) (2011-2017) problems

ElectricalHigh severity💬 Owner reports

A broken steering column spring, coupled with insufficiently earthed wiring, may lead to a short circuit and inadvertent deployment of the driver's airbag. This was subject to a voluntary recall by Mercedes-Benz.

Rough guide
£0 (free safety recall)

Typical symptoms

  • Airbag warning light appearing on the dashboard
  • Unexpected airbag deployment

Affected vehicles

Engines:
All variants
Typical mileage:
All mileages miles
🔍 We have a specific pre-purchase check for this faultCheck an advert →

Mercedes-Benz B-Class service intervals: cambelt, chain and gearbox oil

An overdue cambelt is the most expensive thing a seller can fail to mention on a used B-Class. These are the figures UK specialists work to.

Timing belt (cambelt)Belt
1.5 DCI, 1.5 CDI, OM607, K9K
60,000 miles or 5 years, whichever comes first

Renault-sourced engine, and the engine maker's guidance is the shorter one: Renault specifies the belt at 60,000 miles or 5 years, whichever comes first, while a Mercedes dealer schedule quoted 100,000 miles / 5 years and was later revised to 124,000 miles / 10 years. The 60,000-mile Renault figure is recorded. Rubber degrades with age so the 5-year limit is the critical one.

Timing chainChain
M270, M274, 1.6 TURBO, W176, W246
No fixed replacement interval

Dual-stage chain system: an upper cam chain plus a lower oil-pump and balance-shaft chain. Cam phasers (Y49/1, Y49/2) wear from around 60,000-80,000 km giving a cold-start tick; chain and guide wear shows from about 80,000 km on urban short-trip cars but 120,000-140,000 km on motorway cars. A metallic cold-start rattle needs prompt attention. The M274 DE16 is the longitudinal C-Class version of the same 1.6.

Always confirm against the vehicle handbook. Intervals vary by engine, and several manufacturers revised theirs after failures in service.

Repair costs are typical UK ranges, not quotes. Actual cost depends on condition and garage.Data last verified: September 2026

Where this Mercedes-Benz B-Class fault data comes from

If you used to check the Honest John “Good & Bad” section before the site closed in 2026, this page is where that information now lives. We rebuilt the Mercedes-Benz B-Class owner-report history from the archived Honest John dataset, added our own research, specialist and owner-club sources and DVSA recall data, and we keep it free. Each fault above is badged with its source. The same data feeds our free advert check, which reads a listing against every known fault for the exact engine and year.

CarAdCheck is not affiliated with Honest John or Volkswagen Financial Services. What happened to Honest John, and where each feature lives now.

Before you go and see it

Knowing what a Mercedes-Benz B-Class goes wrong with is half of it. The rest is reading the advert and checking the car's history before you hand any money over.

How to find a car's previous adverts13 min readThe most economical used cars in the real world, not the brochure9 min readThe Honest John alternative: how to research a used car for free8 min read
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Other Mercedes-Benz models

E-Class25 known faultsC-Class23 known faultsA-Class13 known faultsSLK7 known faults