A check-engine light, a rough idle, and a P0016 stored in the engine control unit. On a 2005 to 2008 Mercedes with the M272 V6 or M273 V8, that trio points at a balance shaft gear that has worn its teeth down. It isn’t a sensor. It’s a teardown.
Owners put this one off, and AAA has measured how common that instinct is: roughly 35 million U.S. drivers skipped or delayed needed vehicle maintenance and repairs in a single year. With a balance shaft, delay changes the price. A worn gear sheds metal into the oil and takes the chain and cam adjusters with it.
Quick Summary: Key Takeaways
- Which engines: 2005 to 2008 M272 V6 and M273 V8 engines built before Mercedes changed the gear material are the ones that fail.
- The telltale codes: P0016, P0017, and P0018 mean the crankshaft and camshaft position signals no longer line up.
- Check the engine number: Mercedes published serial-number cutoffs, and anything above the cutoff already has the corrected hardened gear.
- Real cost: The engine comes out and the timing case opens, so budget $4,000 to $7,000 depending on model and what else is worn.
- Do it once: Replace the chain, tensioner, and cam adjusters along with the shaft, because reusing worn timing parts guarantees a repeat visit.
Soft gear teeth cause M272 and M273 timing faults
Mercedes used a gear that was too soft. The balance shaft in the M272 and the idler gear in the M273 both drive off the crankshaft, and in the early production run those teeth round over. Cams then drift out of phase. Timing goes with them.
Nothing you did caused it. Oil changes every 7,500 miles don’t prevent it, and neither does gentle driving, which is why a 90,000-mile C350 and a 150,000-mile ML350 can arrive on the same week with the same code. It’s a build-date problem.
Rough idle and correlation codes are the first real symptoms
P0016 is the headline. Under it sits a cold rough idle that smooths after a minute, a small loss of power, sometimes a hard start, and later a rattle from the timing cover. Some cars stall.
On an S550 or CLS550 with the M273, the fault often appears intermittently for months before it sets permanently, and that window is where the repair is cheapest. Once the code is hard, the chain is usually shot too. Catch it early.
Your engine number decides whether you have the bad gear
Check the number before you panic. Mercedes stamped a serial on the block, and production above the published cutoff carries the revised hardened gear, while anything below it sits in the affected range. Ten minutes settles it.
We pull that number at 2232 Old Middlefield Way and cross-check it against the fault history in the engine and transmission modules. Some cars with a P0016 have a stretched chain or a failed cam adjuster magnet instead, and that distinction is a $600 repair against a $5,000 one. Measure, then quote. Nobody should price a balance shaft off a code reader alone.
Skipping the repair ends with metal in the oil and a dead engine
A worn gear doesn’t hold still. Every mile grinds more material off those teeth, and the filings travel through the oil pump into the cam adjusters, the chain tensioner, and the bearings. Eventually the cams slip far enough that the engine won’t start. Then it’s over.
At that point the quote changes to a used engine at $5,500 to $9,000 plus installation. Drive it less, not more. A car showing this code belongs on a flatbed rather than a commute up El Camino Real.
How our Mountain View shop handles a balance shaft job
The engine comes out, and we plan for it. A balance shaft on an M272 means pulling the engine, opening the timing case, replacing the shaft and gear, then renewing the primary chain, tensioner, guides, and both cam adjuster gears while everything is exposed. Shortcuts cost twice.
Andy and Erin’s crew has rebuilt German engines here for close to 28 years, and each of these jobs leaves with fresh oil, a cleaned pan, and a road test before you get the keys. Customers come from Mountain View, Palo Alto, Cupertino, and Saratoga for work the dealer quotes at nearly double. One teardown, done right.
Frequently Asked Questions
Q: What does code P0016 mean on a Mercedes?
A: It means the crankshaft and camshaft position sensors disagree. On a 2005 to 2008 M272 or M273 engine, the usual cause is a worn balance shaft or idler gear that let the cams drift out of time. A stretched timing chain or a failed cam adjuster sets the same code, so the engine number and a live timing measurement come first.
Q: Which Mercedes models have the M272 balance shaft problem?
A: Early C350, E350, ML350, R350, SLK350, and CLK350 models with the M272 V6, plus S550, CLS550, GL450, and ML550 models with the M273 V8, generally 2005 through 2008. Engines built after the published serial-number cutoff use the corrected gear.
Q: Can I drive my Mercedes with a balance shaft code?
A: Only as far as a shop. Every mile grinds more metal off the gear and sends filings through the oil system. Cars driven for months on a P0016 often need a used engine instead of a timing repair.
Have the engine number checked before you accept a quote
A P0016 on a 2007 Mercedes deserves ten minutes of real diagnosis. Book time at our Old Middlefield Way shop and we’ll pull the engine serial, measure actual cam timing, and tell you whether you’re facing a balance shaft or something far cheaper.
Hours: Mon–Fri 7:30 AM – 5:00 PM; closed Saturday and Sunday
Website: bavariumautoworks.com