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 / destruction.

Note that while this condition is preventable, and remediable if caught early enough; when not investigated in a timely fashion, the bill to resolve the domino effect from the oil leakage will amount to over $12,000 in parts & labor, depending on the engine variant, and what may be determined to need replacement as “incidental” parts / labor throughout the operation.

Let me just sidebar real quick, and personally attest to the overall quality of the 276/278 motors from Benz. They are a true marvel of engineering. With their versatile placement, these power plants were installed in everything from the C class all the way up to the E63S AMG S, and everything in between, 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.

This new tech finding involves the leakage of seals at the camshaft solenoid adjusters, and upper timing cover on these motors. Without getting too far off base, the 8 cylinder variant engines generally see more incidentals with this service remediation operation, due to the tighter package and subsequent wear of things like turbocharger cooling hoses, thermostat, and various additional seals often needing replacement.

A little background on the purpose / function of camshaft position sensors and adjuster magnets: These components play a vital role in fuel economy for modern motors. While two banks are required in a “V” motor configuration, 4 banks fine tune the timing further, which in turn allows for the direct injection engine to deliver optimal fuel economy, by way of constant monitoring, and adjusting air/fuel ratios on-the-fly.

In the above finding / scenario, the engine oil begins to leak externally (onto the engine and other exposed areal components), and subsequently causes oil seepage or leakage, which eventually makes its way down to rubberized cooling hoses and the accessory drive belt, causing swelling and/or slippage. This was our regular condition-based finding with these motors, but more recently; we’ve needed to expand the recommendation of this important service due to a far more dire concern.

We’ve begun to find that this issue extends further, to the camshaft position sensors (the smaller camshaft position magnets), and the leakage is not external (so it’s not immediately obvious), it’s internal, and is causing oil to physically wick into the electrical connectors, subsequently running the length of the engine harness (down to the engine computer). This ultimately leads to engine computer failure, resulting in the high dollar costs outlined in the second paragraph of this blog post.

The aforementioned issues had actually been a minor concern on the predecessor V6/V8 motors (M272/M273), but were less common, and generally didn’t result in the massive headaches that are now being induced with the *new* generation 6 cylinder, 8 cylinder, and potentially 4 cylinder engines… though the 4 cylinder speculation might be a stretch, more so based on a hunch of internal knowledge that has yet to mature. That’s a subject for another potential later blog post.

Regardless, we urge all owners of 2013-2019 Mercedes cars with a V6, and 2011-2019 Mercedes cars with V8 motors to schedule your MB vehicle for a routine checkup, with a particular inspection of these sensors, and replacement (whether preventive, or reactive). The sooner, the better.

The purpose of this blog post is not to point fingers at the manufacturer, it is to raise acute awareness of this increasingly more common finding, so that more of the affected vehicles will have a fighting chance at proactive services being rendered, rather than reactive.

Categories: Electrical, Engine, Fuel Efficiency