Mercedes Benz
117,862 MOT tests analysed. lands in the middle of the pack — here's where B Classs pass, fail, and end up on the retest sheet.
That's 0.9 points below the UK fleet average across our 1,984 tracked models — buyers should expect more first-time fails than the typical UK car.
Pass
76.6%
Pass-after-fix
3.9%
Fail
18.9%
Avg miles
75,696
Pass + Pass-after-fix + Fail = 100%
Some examples of this model are borderline — a small number of diesels were certified Euro 6 before September 2015. Check your registration on the government's ULEZ checker to be certain. Daily charges if driven in the zone: London £12.50 · Birmingham £8.00 · Bristol £9.00 .
Performance by cohort
2 year bands · 117,826 tests
Pass rate climbs 13.2 points across the cohorts — newer B Class examples clear the test more reliably than the early cars.
Pass
76.1%
Fail
19.4%
PRS
4.0%
Avg mileage at test
77,450 mi
Pass
89.3%
Fail
8.7%
PRS
1.7%
Avg mileage at test
35,956 mi
Cohort = vehicle's first-registration year band. Same model, different generations of build.
The picture
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.
ABI Insurance Group
Above average — worth comparing quotes before buying. Lower groups cost less to insure; UK fleet average is around Group 22.
Source: ABI Group Rating Panel · administered by Thatcham Research · groups cover standard variants; performance trims may sit higher. Browse all insurance groups →
20–32
out of 50
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A suspension joint dust cover severely deteriorated
3,182 occurrences · 2.7% of tests
A transmission shaft constant velocity joint boot severely deteriorated
3,127 occurrences · 2.7% of tests
A spring or spring component fractured or seriously weakened
2,957 occurrences · 2.5% of tests
A suspension joint dust cover missing or no longer prevents the ingress of dirt etc
2,351 occurrences · 2.0% of tests
Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view
2,265 occurrences · 1.9% of tests
A rear registration plate lamp or light source missing or inoperative in the case of multiple lamps or light sources
2,071 occurrences · 1.8% of tests
A transmission shaft constant velocity joint boot missing or no longer prevents the ingress of dirt etc
2,021 occurrences · 1.7% of tests
A suspension pin, bush or joint excessively worn
1,769 occurrences · 1.5% of tests
Brake pipe damaged or excessively corroded
1,646 occurrences · 1.4% of tests
A rear registration plate lamp or light source missing or inoperative in the case of a single lamp or all lamps
1,556 occurrences · 1.3% 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 3 failures
£240–£720
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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Build your own retest budget.
Year-band analysis
First-time MOT pass rate split by registration band. A 13.2-point gap between bands means the year you buy Mercedes Benz B Class has a real effect on what turns up at the garage.
Best band to buy
89.3%
2018–2020 registration
the 2018–2020 band climbs to 89.3% — a 13.2-point improvement. Tests in this band average 35,956 miles — roughly 41K miles fewer on the clock than the older band. Failures here are mostly wear items: has a cut in excess of the…, inoperative in the case of multiple lamps… — the structural issues that drag down older examples don't appear in the top-10 for this band. The stricter post-2018 MOT test rules meant manufacturers had to tighten up emissions and electrical checks, but this band still shows far fewer major failures on suspension and bodywork than the older fleet.
Band to be cautious about
76.1%
Pre-2018 registration
On the older band (pre-2018), the data shows a 76.1% pass rate against a fleet average of 89.3% on the newer band. The main culprits logged at test: ball joint dust cover severely deteriorated, constant velocity boot severely deteriorated, and fractured or broken. Average mileage on test for this band is 77,450 miles — high-mileage wear items are a recurring theme.
Best band to buy: 2018-2020 (89.3% first-time pass). Worst band to avoid: pre-2018 (76.1% pass). That's a 13.2-point spread across 112,866 older tests and 4,960 newer ones — year of build makes a material difference on this model.
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Owner reports · Honest John
Verbatim faults logged by owners on honestjohn.co.uk over recent years. We didn't summarise — these are the words people typed in.
Where it falls short
Owner reports (1 entries) flag recurring problems with gearbox/clutch, suspension, electrical faults.
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
Recall history
The B Class has 22 official UK vehicle recalls covering defect details, remedies, and affected build dates.
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.
