Why does my 2013–2015 Mercedes GLK 350 rattle when I start it?

Short answer: On the 2013–2015 GLK 350's M276 V6, a rattle for a second or two on startup usually comes from a worn camshaft adjuster (the gear on the end of each camshaft that changes valve timing) or the timing chain tensioner. If it goes on, the adjuster's tone ring can slip and set code P0016 with reduced power. One owner who fixed his says the right intake adjuster is the one that fails most.

Symptom: A rattle or grinding for a few seconds right after a cold start, sometimes with a check-engine light, code P0016 or P0017, and the engine feeling down on power.

What to check first

1. Read the codes. P0016 and P0017 mean cam and crank timing don't line up.
2. Note when the rattle happens. A short startup rattle that fades points to adjusters or the tensioner.
3. Ask for a cam adjuster and tone ring inspection before agreeing to a full timing job.
4. Get a second quote. Owners report very high dealer estimates.

Likely causes

1. Worn camshaft adjuster (often the right intake). A BenzWorld owner found the right intake adjuster bad, and replacing it fixed the rattle.
2. Camshaft tone ring slipped out of position. The same owner found the tone ring (a toothed ring the cam sensor reads) had moved, which caused P0016.
3. Timing chain tensioner. An MBWorld owner replaced both banks' adjusters and the tensioners. Startup got better but some chain slap remained.

What it usually costs

One BenzWorld owner said the dealer quoted about $5,000–$10,000 on a 2014 with 206,000 miles. He did it himself for about $150 using a $90 aftermarket adjuster, but that took advanced skill and special tools. Get a written diagnosis before agreeing to a big timing job.

Is it safe to keep driving?

Usually in the short term, but don't ignore it. If the timing slips further you can lose power or damage the engine. Get it diagnosed soon. Verify with a mechanic.

DIY or shop?

Shop for most people. Owners who did it themselves had cam locking tools and experience.

Recalls, bulletins and complaints in plain words

• No recall covers the startup rattle in NHTSA's data.
• NHTSA complaints: 1 keyword-matched complaints for Mercedes-Benz GLK-Class 2010–2015 (of 951 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-17; keywords: rattle, timing, camshaft, cam shaft, adjuster, p0016, p0017, noise on start, startup, start up, cold start) (the M276 engine is in 2013–2015 models).

What owners report

• In BenzWorld's GLK-350 startup rattle, CEL, P0016 code, low power fix, a 2014 owner at 206,000 miles had the rattle, P0016 and low power. He found the right intake adjuster bad and its tone ring shifted, reset and secured the ring, and installed a new adjuster. The rattle and code went away.
• On MBWorld, an owner reported chain slap persisting after replacing adjusters and tensioners. Startup was better but not perfect. Another owner posted an M276 bank 2 intake adjuster sprocket video diagnosis.

My take

My advice as a former finance manager: if you're buying a used GLK 350, a cold start is the whole test. If it rattles, use it to negotiate or walk away, because the repair quotes owners got can be more than an older GLK is worth.

Vehicle focus: 2013–2015 Mercedes-Benz GLK 350 with the M276 3.5L V6.

Safety / mechanic note

Timing problems can lead to power loss or engine damage. Verify with a mechanic.