The Mercedes M276 served as the go-to engine in a ton of upper-tier Mercedes cars and SUVs from 2010-2018 and was a formidable workhorse overall. It is looked at as a fairly reliable engine series, with only a few notable problems to take into account. In this article, we’re covering one of those issues which is the notorious Mercedes M276 timing chain rattle issue.
What Causes Mercedes Timing Chain Rattle?
There are actually a number of different faults that can lead to timing chain rattle on startup. The first, and most prevalent cause of timing chain rattle is an insufficient amount of oil reaching the timing chain tensioners during startup. The issue actually became so common that there are multiple technical service bulletins about it. It can also be caused by one of the variable valve timing cam adjusters failing, which causes the engine to skip timing.
Insufficient Oil To Secondary Timing Chain Tensioners
The most common explanation, and the one listed by Mercedes in a number of service bulletins, has to do with insufficient oil on the secondary timing chains tensioners at startup, causing the rattling noise. The idea is that if the vehicle has been sitting for a while, oil will drain from the timing covers to the sump, requiring it to be pumped back to the timing chain tensioners when the vehicle is turned on again. Since that process requires a couple of seconds, there is a period where the chains have excess slack, causing them to rattle before oil pressure builds in the tensioners.
The remedy for that issue is relatively simple. On early M276 engines (engines up to serial number 276 8xx 30 000790), check valves need to be installed in the tensioner oil supply openings on both the left and right side cylinder head. The check valves prevent all of the oil from leaving the front timing covers, allowing oil to remain in the tensioners. Additionally, Mercedes redesigned the M276 timing chain tensioners to a newer design in the middle of the engine’s build cycle. The technical service bulletin also states to replace the old tensioners with the new ones on older engines.
On newer M276 engines (serial number 276 8xx 30 000791 and later), only the check valves need to be installed. While this remedy did solve the issue for some people, others continued to experience timing chain rattle issues caused by another aspect of the timing system.
Intake Cam Adjuster Failure
There is actually a less talked about cause of timing chain rattle on the M276 which seems to be just as prevalent as tensioner issues. This one has to do with the engine’s variable valve timing system. To actuate the VVT system, each cylinder bank has an intake and exhaust cam adjuster, also known as a VVT sprocket, which makes adjustments to cam position. There is an internal pin inside of the adjusters that ensures that the camshafts stay in time. Over time, those pins wear down, allowing the adjusters to skip or jump, causing timing to also be off.
On most M276 engines, this failure almost always happens on the intake cam adjusters which will result in either a P002177 or P001885 engine code. If you are experiencing startup rattle and your vehicle is displaying one of those codes, there is a very good chance that one of the intake cam adjusters has failed and thrown the timing off.
While it isn’t necessarily an easy problem to diagnose, it is relatively straightforward to see if one of your cam adjusters has failed once you take off the front timing covers. You simply have to locate the cam adjuster and manually turn the crankshaft until the adjuster makes a full revolution. If the adjuster is faulty, you’ll hear a very noticeable audible clunk meaning that it has jumped timing. If that is the case, a faulty cam adjuster is almost certainly your issue. I’ll leave a video showing what a failed intake cam adjuster sounds like when it skips timing.
- Rattling on startup then subsiding after a few seconds
- P002177 or P001885 fault codes
- Poor performance or bogging under throttle
In most cases, startup rattle has little effect on the performance of the car. If the rattle is caused by a faulty tensioner not receiving enough oil initially, the rattle on startup might be the only symptom that you experience, making it more of an annoyance than anything. You aren’t likely to even get an engine code in that case.
In most cases, the only time that you’ll actually see other symptoms manifest is if the rattle is caused by a faulty cam adjuster. Since that has an actual effect on the timing of the engine, the ECU will be able to detect that there is something wrong with the VVT system and store a code. You’ll likely either get a P002177 (camshaft position different from given, given cannot be reached, bank 1 intake) or a P001885 (the position of intake camshaft cylinder bank 2 is implausible relative to the position of crankshaft) engine code. That is in addition to the rattle, of course.
The solution to timing chain rattle depends on what the rattle itself is caused by. In most cases, the rattling sound is caused by oil not reaching the timing chain tensioners immediately at startup in which case check valves need to be installed in addition to new and revised timing chain tensioners also being installed (depending on the engine serial number). You can find the full repair procedure and parts list on the technical service bulletin about the issue which I’ll link here.
If the tensioners are the issue, the repair can still be quite expensive, especially if you take your vehicle to a certified Mercedes repair facility. The parts themselves can range from $400 to $1,200, depending on if you intend on using OEM Mercedes parts and if you want to replace your timing chains in addition to the tensioners. Labor tends to be in the ballpark of $600-$1,000. In all, if you take your car in for service at a Mercedes dealer, you’re in for a hefty repair bill. Seeking a qualified and reputable independent shop is likely the better option from a cost perspective.
The same can be said if the timing chain rattle is caused by the camshaft adjuster. In total, the cost is pretty similar either way, as both jobs require a mechanic to remove the front timing covers and associated parts and diagnose the issues. However, the cam adjuster itself is where things get expensive, as they typically cost around $1,000. It is fair to expect labor costs of around $600-$1,000 here as well.
Timing Chain Failure Is Common But Not The End Of The World
Quickly scrolling through the M276 forums, you’d think that timing chain rattle affects nearly every engine made during its build cycle (similar to the balance shaft issues on the M272 engines), however, it isn’t as common as the internet paints it to be. While timing chain rattle affects early model M276 engines more than late ones, due to the tensioner redesign, there are plenty of high-mileage examples out there that haven’t experienced timing chain rattle.
Timing chain rattle is typically the result of either insufficient oil reaching the timing chain tensioners or a faulty cam adjuster. The former is a pretty straightforward issue to deal with by simply installing check valves and new tensioners. Replacing a faulty VVT cam adjuster is a bit more involved, but still not extremely serious. Ultimately, while timing chain rattle is an annoying issue to have, especially on a Mercedes, it usually doesn’t lead to any serious damage or harm later down the line.
If you are interested in learning more about the Mercedes M276 and its limited but common problems, take a look at our dedicated common problems guide.