On the M272 V6 petrol engines sold between 2004 and 2007 (with engine numbers below 2729..30 468993) the balance shaft gear wears out prematurely, because its material is soft. The gear sits in the drive of the timing chain, so as it wears the valve timing drifts.

The maker's own bulletin gives two fault codes for this: 1200 and 1208. What is typical is that the code comes straight back after being erased, on restart, and that is what sets it apart from a one-off disturbance. The check engine light comes with it, along with uneven running and misfires, and the car can even stop.

For the repair the engine has to come out, but the cylinder heads do not have to come off. The counterweight has to be replaced along with the shaft, and the kit belongs to the displacement: A272 030 00 13 for the 2.5 litre, A272 030 01 13 for the 3.0 and A272 030 02 13 for the 3.5. In the same job the maker calls for the oil pump and the chain tensioner to be replaced, and for all four camshaft adjustment solenoids to be replaced with A272 051 01 77. The chain tensioner is single use: if it is taken out or readjusted after fitting, the chain is over-tightened, and that destroys the cylinder head. The repair is over 4000 dollars, because the labour with the engine removed is around 20 hours.

The complaints turned into a class action in the United States (Suddreth and Dunton versus Mercedes-Benz USA). The court finally dismissed the claim: the gears fail between 60 000 and 80 000 miles (about 95 000 to 130 000 km), that is outside the warranty period, and the maker was not held liable. According to the case material the maker knew about the fault, issued repair bulletins and finally switched to a stronger gear.

If the balance shaft repair is in the service book, the stronger gear is part of it.