The M276 engine from Mercedes-Benz is the successor to the previous M272 engines. It’s also related to the Fiat-Chrysler 3.6L Pentastar V6 engine since Mercedes was owned by FCA at the time. Mercedes also offers multiple variants of the M276 – a 3.5L NA, 3.0L twin turbo, and 3.5L twin turbo. They’re all great options that offer a good balance of performance, efficiency, and reliability. However, the engine is still prone to a few common faults. In this article, I discuss common problems with the Mercedes-Benz M276 V6 engine and overall reliability.
M276 Engine Problems
- Carbon build-up
- Timing chain tensioner
- Plugs & coils
We’ll discuss the above issues in greater depth throughout the rest of the article. However, it’s a good time to add a few quick notes. The M276 engines are all pretty reliable engines. We’re classifying these as the most common problems for good reason. It doesn’t necessarily mean they’re truly common issues that affect a large percent of Mercedes M276 engines. Rather, when problems occur these are a few of the common areas.
There are a few different variants of the M276 including the DE35 NA, DE30 twin turbo, and DE35LA twin turbo. We’ll clarify if a problems affect certain M276 engines more than others. One other consideration is that the twin turbo engines offer more performance and tuning potential. However, turbo M276 engines will generally cost more to maintain than the naturally aspirated variant.
If you would rather consume this content via a video, check out our Mercedes-Benz M276 Common Problems video below:
1) HPFP Issues
As a direct injection (DI) engine the Mercedes M276 V6 uses a high-pressure fuel system. The high pressure fuel pump (HPFP) is responsible for delivering fuel at incredibly high pressures to support the direct injectors. HPFP failures aren’t unheard of by any means. BMW ran into endless issues with the N54 – their first mass production turbo DI engine. VW had quite a few problems early on, too.
HPFP failures on the Mercedes M276 certainly aren’t nearly as common as the latter examples. However, HPFP problems can and do occur. It seems more and more cases pop up as some of the early engine keep aging. Anyway, this failure is far from being a truly common issue but it’s something to be aware of.
When the high pressure fuel pump starts failing you’ll notice quite a few symptoms. Fortunately, the M276 HPFP rarely fails suddenly but rather over the course of a couple months or even years. Some run into issues as early as 30,000 miles, but most HPFP failures will likely occur north of 80,000 miles.
Symptoms of M276 HPFP Failure
- Long crank
- Engine fault codes / CEL
- Stuttering / hesitation
- Rough idle
- Power loss
One of the first signs of HPFP failure is an unusually long crank, especially on cold starts. Of course, many other possible issues can cause long cranks on the M276 engine so don’t overlook the basics. Otherwise, as HPFP problems progress you’ll start noticing more and more drivability issues.
Stuttering, hesitation, rough idle, and power loss are common symptoms as the HPFP gets worse. Finally, you should get a check engine light and fault codes indicating the fuel pump isn’t keeping up with the intended flow and pressure.
Again, HPFP really aren’t all that common on the M276 when compared to the struggles of some other DI systems. More good news is that the fuel pump is pretty cheap at about $300-600. It’s also not a complicated repair for the DIY crowd, but labor can add in another chunk of money for the repair shop crowd.
2) Carbon Build-Up
Carbon build-up is another interesting topic related to direct injection. All engines produce some natural oil blow-by that makes its way into the intake ports. With traditional port injection (PI) fuel is sprayed into the intake ports. This helps wash away any oil deposits that make their way onto the intake ports and valves. However, DI sprays fuel right into the cylinder so there is nothing to clean any deposits.
We mentioned the N54 engine and VW/Audi in the previous section. Those same engines ran into excess carbon build-up as early as 40,000 to 60,000 miles. Mercedes did a lot better with their M276 V6 engine. You’ll find some that claim carbon build-up is not an issue at all. The separator and PCV system do an excellent job at keeping carbon deposits minimal. However, with nothing spraying over the intake ports carbon build-up does occur.
Exactly when this will cause issues is still up for debate. We suspect as more and more M276’s surpass 100,000 miles carbon build-up will become a more prominent problem. It’s a pretty minor “problem” in the grand scheme, and some engines will probably go their whole lives without carbon cleaning. Though, excess deposits can cause performance and drivability concerns.
The twin turbo DE35LA and DE30 are more prone to carbon build-up than the NA DE35 engine. Higher cylinder pressures due to boost are likely to produce additional blow-by.
Carbon Build-Up Symptoms
- Rough idle
- Stuttering / hesitation
- Power loss
As carbon build-up on intake valves and ports it begins to restrict air-flow into the cylinders. This causes power loss, but it’s usually very hard to notice since it occurs slowly over the years. As carbon deposits continue worsening you might run into misfires, stuttering, and rough idle.
M276 Carbon Build-Up “Fix”
Coming from the BMW N54 world we’re very very familiar with carbon build-up and cleaning methods. The tried and true method is walnut blasting the intake ports. This involves a heavy-duty shop vac and walnut media shells. Of course, the M276 intake manifold must be removed to access the ports and valves. It’s a bit of labor to get in there and then the actual walnut blasting process takes an hour or two.
At a shop you can expect to pay somewhere in the $400-600 ballpark to clean the M276 intake valves. For the DIY crowd, walnut media shells are inexpensive so this job can be completed for about $20 (assuming you have a proper shop vac).
3) Timing Chain Tensioners
Some M276 engines run into issues with rattling on start-up. Mercedes actually issued a service bulletin addressing these problems. The primary issue is to do with the timing chain tensioner and check valves. Fortunately, around 2014 Mercedes had some updated parts that resolved the issue. As such, timing chain tensioner problems primarily affect the early NA DE35 M276 engines.
Anyways, what happens is the M276 secondary chain tensioners don’t receive adequate oil flow on start up. This leads to the rattling sounds until oil pressure builds up enough. Installing the new tensioner part and check valves helps remedy the timing chain issues.
Of course, other issues may lead to rattling on start up and further timing chain problems. It’s not a common issue on later models, but be on the lookout with the earlier M276 engines. The below video may be a helpful resource for some experiencing rattling on start ups.
Timing Chain Tensioner Symptoms
- Fault codes
- Poor operation
Rattling is the primary symptom of the issue at hand we’re discussing with the tensioners lacking oil flow on start up. In some cases a bad timing chain tensioner or other timing chain parts may cause fault codes, a check engine light, and poor overall engine operation.
Timing Chain Tensioner Replacement
The updated tensioners and check valves are fairly cheap for just the parts. Labor can add quite a bit of money on top. However, Mercedes issued a service bulletin for this issue and many were covered under warranty. If you run into this problem out of warranty then Mercedes may be willing to work with you and help with the repair bill.
4) Ignition System Problems
Alright. This isn’t something we classify as a problem in the first place. Spark plugs and ignition coils are standard maintenance on almost any engine. Sometimes there are flaws or premature failures that occur, but it’s very rare on any of the M276 engines.
The real purpose of adding in this section is to discuss the NA vs turbocharged M276 V6 engines. Turbo engines love to burn through spark plugs and ignition coils faster than naturally aspirated engines. Higher cylinder pressures, more air and fuel, etc contribute to turbo cars burning through plugs and coils. The lifespan is likely about half that of NA engines. It’s especially true when you start tuning and modding the twin turbo engines.
Anyway, plugs and coils aren’t truly problems on the M276 engine. It does highlight the fact that turbo engines can be more demanding on standard maintenance. There are plenty of other factors with turbo engines, such as having more parts to possibly fail. We love turbo engines and would choose the Mercedes 3.0 or 3.5L twin turbo engine any day. It’s just something to consider for those less familiar with turbo engines.
Plugs & Coils Symptoms
- Rough idle
- Power loss
As spark plugs and ignition coils wear down occasional misfires are typically the first sign it’s time to replace them. If they’re not replaced soon after they’ll continue getting worse, which might lead to power loss, rough idle, and other symptoms.
Plugs & Coils Replacement
Ignition coils and spark plugs are very easy to replace on most engines, including the Mercedes V6 M276. Even novice DIY’ers can knock out the job fairly easily. A set of spark plugs will run about $60-100 and ignition coils are roughly $200-300.
On the DE35, the plugs should last about 70,000 miles and ignition coils twice that long. The turbo M276 DE30 and DE35LA will need plugs every 50,000 miles or sooner while coils also last about twice as long.
M276 Engine Reliability
How reliable is the Mercedes M276 V6 engine? We’ll give the engine average to above average remarks for reliability. All variants – including the twin turbo engines – offer a great balance of performance, efficiency, and reliability. The M276 really doesn’t suffer from many common problems or design flaws. Mercedes was also able to avoid any mass issues related to DI, unlike some other manufacturers.
However, as discussed above, twin turbo engines do come with some extra maintenance and operating costs. The M276 DE30 and DE35LA are still awesome engines all around. Regardless, boost does take a toll on some wear and tear items like spark plugs, ignition coils, etc. There are also more parts that can potentially fail, but there don’t seem to be any common turbo related problems.
Some reliability simply comes down to luck of the draw. However, maintenance is one thing we do have control over. Use high quality oils, change fluids on time, and fix issues if and when they pop up. Maintain the Mercedes-Benz M276 engine well and it will likely reward you with a fun and reliable experience.
The Mercedes-Benz M276 engine family has a lot to offer. A 3.5L naturally aspirated V6, 3.0L twin turbo V6, and 3.5L twin turbo V6. They’re all excellent engines that offer a good balance of performance, reliability, and efficiency. However, no engine is perfect and that applies to the M276 as well.
Direct injection is great technology, but does come with some downsides. It seems HPFP failures are becoming more common as the engine continues to age, though problems are still far and few between. Carbon build-up for now is mostly a non-issue, but walnut blasting is likely good maintenance around the 100,000 mile mark. Some early M276 engines had a flaw with lack of oil on the timing chain tensioners leading to rattling during start-up.
Otherwise, I discussed spark plugs and ignition coils to highlight the fact turbo engines can be a bit harder on maintenance. The Mercedes M276 twin turbo engines are proving to be pretty reliable, though. Maintain the M276 well and it’s likely to be an excellent, reliable engine that you can enjoy for years to come.