The picture
Spring and CV boot failures at 71,951 average miles
Fractured spring components lead the Mercedes-Benz B-Class MOT failure list, followed by deteriorated CV joint boots and suspension joint dust covers. Across 80,901 tests at an average of 71,951 miles, a 76.14% pass rate sits in acceptable territory for a compact MPV of this age and price point. The failure pattern is consistent with under-maintained rubber and ageing suspension components.
Owner reports from the 2019 B180 AMG Line with the new 1,332cc four-cylinder engine flagged a clunking from the lower front driver's side — investigated by Mercedes, unresolved. The same car had a full list of additional snags reported within months of delivery. Clunking noises near the front suspension and fractured springs are rarely unrelated; if the noise is there, the spring needs checking before MOT day. CV boots can split quietly and go unnoticed. A straightforward pre-MOT inspection covers all three failure areas in under an hour.
Top ten reasons for rejection.
- 01
A spring or spring component fractured or seriously weakened
2,978 occurrences · 3.7% of tests
- 02
A transmission shaft constant velocity joint boot severely deteriorated
2,581 occurrences · 3.2% of tests
- 03
A suspension joint dust cover severely deteriorated
2,363 occurrences · 2.9% of tests
- 04
A transmission shaft constant velocity joint boot missing or no longer prevents the ingress of dirt etc
1,739 occurrences · 2.1% of tests
- 05
Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view
1,723 occurrences · 2.1% of tests
- 06
A rear registration plate lamp or light source missing or inoperative in the case of multiple lamps or light sources
1,697 occurrences · 2.1% of tests
- 07
A suspension joint dust cover missing or no longer prevents the ingress of dirt etc
1,676 occurrences · 2.1% of tests
- 08
Brake pipe damaged or excessively corroded
1,580 occurrences · 2.0% of tests
- 09
A suspension pin, bush or joint excessively worn
1,470 occurrences · 1.8% of tests
- 10
Tyre tread depth not in accordance with the requirements
1,345 occurrences · 1.7% of tests
Counts cover Major and Dangerous defects logged at test. Advisory items excluded so this shows why a car was rejected, not just what the tester flagged in passing.
Worst-case fix budget · top 2 failures
£160–£480
If every one of this B Class's most-logged Major fails hit at the same MOT, that's the real-world UK garage range. Reality is usually one or two items, not all of them. Open the estimator →
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Owner reports · Honest John
What owners actually report.
Verbatim faults logged by owners on honestjohn.co.uk over recent years. We didn't summarise — these are the words people typed in.
Recent owner-reported faults
- 16 Oct 2019
Owner supplied list of faults found with new Mercedes-Benz B180 AMG Line Premium Auto (with the new 1,332cc 4-cylinder petrol engine) purchased in May 2019: 1. Occasional “clunking” noise that appears to be from the lower front on the driver’s side. Mercedes Response: "Despite several road tests and checking the full suspension and running gear we have not been able to find or replicate the complaint." 2. Engine surges on taking-up drive intermittently, and especially when moving off from cold. Mercedes Response: "Despite several road tests from cold and a full electrical diagnostic we have not been able to find fault or replicate the complaint. My technician has noted the drive/engine is normal. We have updated the control unit with the latest software on this engine and gearbox control units." 3. Reverse gear selection is not positive intermittently, sometimes repeated selection is necessary to engage reverse gear, and this occasionally affects Drive selection. Mercedes Response: "Despite several road tests from cold and a full electrical diagnostic we have not been able to find fault or replicate the complaint. My technician has noted the drive/engine is normal." 4. Keyless locking does not always function on driver exiting car, repeat attempts to lock needed or use fob button. Mercedes Response: "We have been unable to fault the system. As discussed I feel this is a characteristic of the vehicle." 5. Hazard proximity alarm sensors are too sensitive, constant alarm sounds when adequate hazard clearance exists. Mercedes Response: "We found the Parktronic control unit was defective, It has been replaced with a new Parktronic control unit. 6. Hazard proximity alarm sensors sound intermittently when completely clear of obstacles, and also seems to detect pavement/driveway access as hazards. Mercedes Response: "As above. We found the Parktronic control unit was defective, It has been replaced with a new Parktronic control unit." 7. Driver’s side wiper blade appears to catch on windscreen outer frame surround intermittently, depending on extent of rain. Mercedes Response: "We found the wiper arms required adjusting, We set to correct adjustment." 8. Starguard Body Protection coating, has resulted in excessive residue being present on non-metallic trim which is very difficult to remove, and also coating not polished off the body fully. Mercedes Response: "This has not been done yet, We will valet the car before you collect it." 9. Owner’s Handbook pages bent backwards inside document wallet, reported on collection of car. Mercedes Response: "Supplied new owners hand book." 10. Mercedes Type ‘C’ connector lead missing on collection of car, but replacement has been provided. * Terms and Conditions * Privacy * Cookies * Advertise on this site * Contact * Mobile) Website of the Year 2016, 2017 & 2018
Source: honestjohn.co.uk · 1 reports indexed
Buying or keeping a B Class?
Use the failure ranking as a pre-test checklist or a haggling lever. Treat the headline pass rate as a fleet-wide trend, not a guarantee on any individual car.
If you own a B Class and your last MOT looked nothing like the ranked failures above, that's normal — individual cars vary widely. The ranking shows the patterns testers flag most often across the country.