Mercedes-Benz CLS: Intake camshaft adjuster failure and timing chain tensioner cold-start rattle (M276 3.5 V6, CLS350)

The M276 3.5 V6 in the CLS350 has two related timing faults. Oil drains back out of the chain tensioners after the car sits, so the chains go slack for a few seconds on a cold start and rattle, and the locking pins inside the intake camshaft adjusters (variable valve timing sprockets) wear until the adjuster jumps, setting cam timing codes such as P002177 or P001885. Early engines (Mercedes lists serial numbers up to roughly 276 8xx 30 000790, so most 2011-2012 CLS350s) are the most affected; Mercedes answered with a technical service bulletin for the rattle after start that adds oil check valves to the tensioner feeds and fits revised tensioners, and that is not a free recall. Left alone, repeated dry starts wear the chain, guides and adjusters, and a slipped adjuster can cause rough running, limp mode or, in the worst case, valve and piston contact.

• Metallic rattle or grinding from the front of the engine for 2 to 5 seconds after a cold start
• Check engine light that comes and goes
• Rough idle or hesitation, worse when cold
• Longer than normal cranking before it fires
• Clunk from the front of the engine on start-up

1. 1

   Ask the seller not to start the car before you arrive and put your hand on the bonnet to confirm it is cold.

2. 2

   Stand at the front with the bonnet open while they start it and listen at the front timing cover: a clatter or rattle lasting more than a second or two that fades as oil pressure builds is the warning sign.

3. 3

   Check the dash for the check engine light once it is running, and on the test drive listen for hesitation or rough running at low revs.

4. 4

   Ask for invoices showing camshaft adjusters, tensioners or tensioner check valves replaced, and check the service book for oil changes at least every 15,000 km with the correct Mercedes 229.5 spec oil.

5. 5

   If a workshop inspection is possible: have a Mercedes-capable scan tool read stored engine codes (P001685, P001785, P002177, P001177, P001885) and the camshaft position actual values, and confirm whether the tensioner check valve update has been done.

Parts involved: Timing chain.

$2,800 to $8,500 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.

• “Has the engine ever rattled on a cold start?”
• “Have the camshaft adjusters or timing chain tensioners been replaced, and do you have the invoice?”
• “Has the tensioner check valve update been done?”
• “How often was the oil changed and with what oil?”

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

• NHTSA technical service bulletin MC-10167488-9999 (M276 rattling noise after engine start for several seconds)
• 8020 Automotive: Mercedes M276 Timing Chain Rattle, Symptoms and Solutions
• Motronix: Mercedes M276 Camshaft Adjuster Failure and Cold Start Rattle
• 603 M-Tech: How to Diagnose Camshaft Adjuster Problems in the Mercedes M276 Engine
• BenzWorld forum thread: M276 Camshaft Adjuster replacement
• Automotive Tech Info: Mercedes-Benz Timing Chain Tensioners