Dear Alex, 

I have a five-year-old Mercedes C-class and I have heard rumours that the subframe is liable to corrosion from the inside. Need I be concerned? The car recently passed an MOT test, but if the corrosion emanates from inside then the fault will not be discovered until it appears on the outside of the subframe. Can you put my mind at rest?

– KP

Dear KP, 

Several Mercedes models, including the C-Class, are prone to rear subframe failure due to rust. However, to date, the issue has tended to affect W203 – and W204-generation C-Classes – that is to say, those built between 1999 and 2014. 

If your car is five years old, then it’s a W205. Thus far, I haven’t seen so many owners reporting subframe problems with this generation. 

That doesn’t necessarily mean you’re out of the woods. It could mean that Mercedes acknowledged the problem and took steps to ensure the W205 doesn’t suffer the same fate as earlier generations. However, it could also mean that these cars simply aren’t old enough to have developed subframe faults in great numbers yet. 

The one piece of reassurance I can provide is that Mercedes is usually pretty good at honouring its bodywork warranty, although it usually stipulates that the car should have had its annual bodywork inspection carried out at a Mercedes dealer, which de facto means it should have a full Mercedes service history.

I have heard of cases where they haven’t maintained this requirement, allowing cars that have not been dealer-serviced to benefit – but that seems to be random. 

For that reason, you might want to keep using a Mercedes dealer for annual servicing, for peace of mind. Even if you don’t, it’s worth having an annual bodywork inspection carried out at a Mercedes dealer.