2021 Mercedes-Benz B 1.9L Diesel · CA21 KCG

B 180d and B 200d cars use the OM654 2.0 diesel with an SCR system that Mercedes Club owners describe as fragile in UK winters: a failed pump, heater or NOx sensor triggers 'Check Service Now' plus an amber engine light, then a mileage countdown that ends with the engine refusing to restart. Carwow lists diesel stalling and reluctance to re-start among the recurring B-Class complaints. One member reported a failed AdBlue pump at 39,000 miles for around £300 fitted, and specialist garages warn the countdown cannot be reset by simply topping up the tank.

DVSA MOT data analysed by Carpeep puts suspension as the second-largest failure category for the B-Class, at 22.4 per cent of all recorded failure items, with a fractured or broken coil spring the single most-common item at 6.8 per cent, followed by ball-joint dust covers no longer keeping dirt out (5.7 per cent) and split driveshaft gaiters (4.2 per cent). UK potholes plus the B-Class's tall, heavy nose accelerate the damage, and Carwow independently lists suspension problems among this car's recurring faults. Listen for knocks and check ride height on all four corners before viewing an older example.