2019 Mercedes-Benz CLS 2.9L Diesel · KC19 HMF

Two DVSA campaigns hit the C257 here. R/2019/281 covered 230 UK cars where the electric line feeding the coolant pump could chafe against the engine fan; R/2021/438 covered 35,624 cars on the 222 and 257 platforms where the coolant pump could leak between the vacuum system and the coolant circuit, with pump replacement as the fix. Specialist CLS guides describe the electric pump and integrated thermostat as the known weak points on the four- and six-cylinder engines, giving overheating warnings and a loss of cabin heat from 50,000 miles, and warn that a vacuum-side leak also degrades brake assist.

DVSA campaign R/2021/110, covering 108,971 UK Mercedes vehicles including the CLS, plus the closely related R/2021/083 for communication-module software, addressed emergency-call behaviour that did not meet specification. BBC News reported the same global action, which covered more than a million cars, because the system could fail to alert emergency services or transmit the wrong position. A separate CLS campaign R/2020/236 covers the eCall system on 3,127 cars. If the SOS lamp is lit or the button gives no response, the work is outstanding.

CLS 300d, 350d and 400d cars run the OM654 and OM656 diesels with full SCR equipment, and DVSA campaign R/2020/243 required engine control unit software updates with NOx sensor replacement where necessary. Mercedes specialists report the characteristic failure pattern: an AdBlue warning, then a countdown stating the engine will not restart after a set number of miles, usually caused by a failed tank heater, delivery pump or NOx sensor rather than an empty tank, and typically first seen in cold weather. Once the countdown expires the car is immobilised and cannot be restarted.