CriticalVery commonEngine

Mercedes-Benz S-Class: M272 / M273 Balance Shaft and Idler Gear Plastic Tooth Failure

M272 / M273 Balance Shaft and Idler Gear Plastic Tooth Failure is a very common engine fault on the Mercedes-Benz S-Class on the 2006–2008 cars, and we rate it critical. Putting it right costs $3,500 to $9,000 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 20 documented faults on the Mercedes-Benz S-Class.

Vehicle: Mercedes-Benz S-Class
Engine: 2.5L / 3.0L / 3.5L / 4.7L / 5.5L
Years: 2006–2008
Fuel: petrol
Gearbox: auto
System: Engine

This page covers the Mercedes-Benz S-Class as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Mercedes-Benz S-Class faults20 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph for this fault yet. We would rather show none than show a picture of something else.

What goes wrong

The M272 3.5 V6 and M273 5.5 V8 petrol engines in the W221 S-Class suffer from a well-documented and catastrophic failure of the balance shaft and idler gear assembly. The gears use a plastic composite tooth profile that degrades, strips, or cracks typically between 80,000 and 130,000 km. When the balance shaft gear fails the debris can cause sudden oil pump drive failure or engine seizure. Mercedes formally acknowledged the fault, extended the warranty period on affected vehicles, and produced a revised steel-tooth replacement gear. Any W221 with unconfirmed original gears above 80,000 km must be treated as high risk.

What you would notice

Sudden increase in engine vibration or rough running
Knocking or rattling from lower engine block
Oil pressure warning light if oil pump drive is affected
Engine failure or seizure in advanced cases

How to check it

Where to look. Lower engine block, balance shaft assembly behind the engine front timing cover

Ask directly whether the balance shaft and idler gear have been replaced with the revised steel-tooth components and request documentation. If the owner cannot confirm and the odometer is above 80,000 km, have an independent Mercedes specialist inspect before committing. Check for any vibration at idle and scan for fault codes. This is the most critical pre-purchase check on any W221.

What it costs to put right

$3,500 to $9,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Have the balance shaft gears been replaced with the revised steel-tooth components?”
“Can you provide documentation of the balance shaft gear inspection or replacement?”
“What is the current odometer reading and what is the full service history?”

Now check the Mercedes-Benz S-Class you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.

Mercedes-Benz S-Class buyer questions

Is m272 / m273 balance shaft and idler gear plastic tooth failure serious on a Mercedes-Benz S-Class?

We rate it critical and very common on the Mercedes-Benz S-Class. The M272 3.5 V6 and M273 5.5 V8 petrol engines in the W221 S-Class suffer from a well-documented and catastrophic failure of the balance shaft and idler gear assembly. The gears use a plastic composite tooth profile that degrades, strips, or cracks typically between 80,000 and 130,000 km. When the balance shaft gear fails the debris can cause sudden oil pump drive failure or engine seizure. Mercedes formally acknowledged the fault, extended the warranty period on affected vehicles, and produced a revised steel-tooth replacement gear. Any W221 with unconfirmed original gears above 80,000 km must be treated as high risk.

How much does it cost to fix on a Mercedes-Benz S-Class?

$3,500 to $9,000 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Mercedes-Benz S-Class years are affected?

Our research records this fault on the 2006–2008 Mercedes-Benz S-Class. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.