Experiencing a startup rattle and struggling to get your Mercedes Benz 2012 E350 smog compliant? A check engine light can be a frustrating indicator of deeper issues. This article details a hands-on, DIY fix for a common problem related to cam sensor misalignment and startup rattle in the Mercedes Benz 2012 E350 model. This repair focuses on addressing a potentially shifted cam sensor wheel, offering a solution that might save you considerable time and expense.
Diagnosing the Cam Sensor Misalignment
The journey began with persistent issues in getting the Mercedes Benz 2012 E350 to pass smog regulations, accompanied by an unsettling startup rattle. To investigate, the intake manifold was removed – a task that became relatively quick with experience, taking only about 30 minutes. The next step involved accessing the cam sensors. All four cam sensors were pulled to visually inspect the alignment marks. Upon inspection, the driver’s side, left bank cam sensor window revealed a slight misalignment.
An example image of a cam sensor location in a Mercedes engine, similar to the E350 model discussed.
This discovery raised questions. Could the timing chain be off by a tooth? Upon closer examination of the timing chain teeth, this seemed unlikely. Recalling information about potential issues with the camshaft sensor wheel shifting on the camshaft, a hypothesis began to form. Could the sensor wheel itself be the culprit?
The “Screwdriver Fix” Experiment
To test this theory, a bold experiment was devised. Using a large, flat-blade screwdriver (18 inches long with a 1/2-inch wide blade), pressure was carefully applied through the sensor hole directly to the cam sensor wheel. The initial application of force yielded no movement. However, with increased pressure, the cam sensor wheel shifted – perhaps a little too much initially, indicating it was indeed movable.
The engine was then rotated until a position was found where the adjuster wheel could be nudged back towards the correct alignment. After rotating the engine approximately four times, the cam sensor window was re-examined. This time, the cam appeared to be in sync. Interestingly, there was a slight offset, but it was identical for both the exhaust and intake cams. This uniform deviation was attributed to the tensioner relaxing due to lower oil pressure with the engine off.
A representative image showing the process of intake manifold removal, a step in accessing the cam sensors for inspection.
Results and Engine Performance
With the cam sensor wheel adjusted, the intake manifold was reinstalled. The moment of truth arrived with the engine restart. The Mercedes Benz 2012 E350 started instantly, crucially without the telltale startup rattle. Even more encouragingly, no check engine light illuminated on the dashboard. A subsequent scan confirmed that the cam was now registering as in sync, and the engine was running and starting perfectly. While a test drive was still pending at this point, initial results were highly promising.
Understanding the Root Cause and Long-Term Implications
The likely explanation for this issue points towards the press-fit design of the cam sensor ring used by Mercedes. This thin metal ring, secured by a press fit, might not be robust enough to withstand certain stresses. The original problem likely stemmed from a failing camshaft adjuster. When these adjusters malfunction, they can rattle and oscillate violently while the engine is running. This “hammering” action is suspected to be the cause of the cam sensor plate shifting its position on the camshaft over time.
With the installation of a new, properly functioning adjuster, the source of the disruptive force is eliminated. The cams are now synchronized, and the engine control unit is operating without error codes. While the possibility of the cam sensor wheel shifting again exists, the force required to move it manually with a screwdriver suggests it is reasonably secure. It is believed that without the repeated impact from a failing adjuster, the wheel should remain in place. If future issues arise, camshaft replacement remains an option.
This DIY repair, from diagnosis to completion, was accomplished in under two hours. Compared to the potentially extensive labor involved in removing valve covers and related components (estimated at 12 hours previously), this approach offers a significantly faster and potentially effective solution for engines experiencing cam sensor wheel misalignment after a cam adjuster failure.
A generic image representing a smoothly running engine, symbolizing the successful outcome of the repair.
Conclusion
The Mercedes Benz 2012 E350 is now running smoothly, quietly, and without any check engine lights. While some might view this “screwdriver fix” as unconventional, it addresses the immediate issue effectively and efficiently. The repair’s longevity remains to be fully determined, but the robust nature of the adjusted sensor wheel suggests a positive outlook, especially with a new cam adjuster in place. This experience offers a valuable insight and a potential time-saving fix for Mercedes Benz 2012 E350 owners facing similar startup rattle and cam sensor related problems.
