Mercedes Owner Faces Cascade of Repair Claims After Stall, Seeks Guidance

A Mercedes driver is sharing a frustrating dealership saga after their car began jerking and stalling, triggering the check engine light and nearly every other dashboard warning. The vehicle was towed to a Mercedes service department, where the initial diagnosis pointed to an engine wiring harness issue affecting cylinders 2 and 4, along with a fuel injector, at a cost of roughly $5,000.

The owner approved the work after being assured it was the definite cause of the stall.

The next day, the dealership said a 48-volt battery also needed replacing for $2,900, a charge the owner reluctantly accepted after being told it was necessary to complete the repair. Two days later, the shop reported contaminated gas and a failing high-pressure fuel pump. At that point, the owner requested documentation, including all diagnostic codes from arrival and a fuel sample test.

After some pushback, the dealership offered to replace the fuel pump for free due to the hassle, but then mentioned a broken chain that would require engine removal, $11,000 in labor, to inspect.

Later, the dealership said the chain wasn't broken, just slipped, without the costly engine removal. Most recently, they suggested replacing the entire engine. The bad-gas claim was also dropped, and the owner agreed to pay $500 for tank draining. The owner is now asking for advice on what additional testing or questions to raise, feeling overwhelmed by the escalating costs and shifting explanations.

One forum commenter notes the wiring harness and 48V battery are known weak points on these engines and advises getting those fixed first, then seeing how the car performs, while recommending a reputable independent shop over the dealer for any further work.