Mercedes-Benz M276/M278 Camshaft Position Sensor Leakage

Posted September 29, 2023

Just as soon as we thought Mercedes-Benz might be able to crawl out of the doghouse, after a sudden extensive subframe recall with their W & X 204 / W 212 poster chassis cars (among others); our team of technicians have begun to encounter irregularities with the engine harnesses / engine computers on the M276/M278 motors, stemming to fluid leakage and subsequent electrical harness damage and failure.

Let me just sidebar real quick, and reminisce in the 276/278 motors themselves. They are phenomenal to pilot (power and balance-wise), and with their versatile placement, versions of this power plant (and its technology) were installed in everything from the C Class all the way up to S63 for several generations. Thanks to direct injection, they’re not only incredible performers, but also achievers of fantastic fuel economy numbers in their segments / classes.

Back to the reality we face though. Once our team began to identify external leakage at routine service visits (Spring 2023), we began performing reactive condition-based services to resolve leakage events at the camshaft / timing cover, which then caused us to discover the internal camshaft position sensor / adjuster solenoid leakage events, which were present on most of the examples we’d encounter.

UPDATED 5/10/24: We are now seeing more and more of these engines with regression, and have acquired more information since our preliminary PSA.

As it turns out, when the internally leaking engine oil migrates to the electrical connectors and engine computer’s electrical pins by way of the harness itself, with heat as the catalyst (caused by the electrical current), the engine will generally begin to misfire / run poorly, and the vehicle will enter a limp-home mode. This ultimately leads to harness and engine computer failure, and additional electrical issues are also likely in systems such as SRS and Ignition, due to the engine computer / harness being linked to the crash sensors, airbag equipment, and spark control circuits on the controller area network bus.

The cost to replace an engine computer and harness on vehicles exhibiting these issues is $8K – $12K in parts & labor (depending on the engine variant), and the components are Mercedes-Benz controlled, meaning that only a dealership can acquire these components and perform the service operation.

A further alarming matter is that Mercedes-Benz has not actually redesigned the components that are causing this issue, which means that performing the service will only potentially “buy you time” until history inevitably repeats itself. We still recommend replacement of these components if there is no active oil in the harness, and the upper timing cover / cam cover is actively leaking.

We urge all owners of 2013-2019 Mercedes cars with a V6, and 2011-2019 Mercedes cars with V8 motors (including the AMG cars) to schedule your MB vehicle with us for a routine checkup, with a purpose driven inspection of these sensors, and advisement based on our findings.

The purpose of this blog post is not to point fingers at Mercedes-Benz, it is to raise acute awareness of this increasingly more common finding, so that owners of the vehicles affected by this alarming situation are educated, and able to make an informed decision about how they are going to react. more of the affected vehicles will have a fighting chance at proactive services being rendered, rather than reactive.

Categories: Electrical, Engine, Fuel Efficiency