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Q: Wiring harness burned up from short circuit to disa valve

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My car wasn’t running well, so I went ahead and took it to an authorized BMW dealer for diagnosis and any repairs needed. They reported to me that my car had burned up the wiring harness that had resulted from a short circuit to the disa valve that is on the engine. Also, the poor performance of my car was also a result of faulty ignition coils in cylinders 1, 3, and 5. They also told me that the vanos valves were stuck and needed replacement.

Last year, before my car was having these problems, at one point the car had filled with smoke and our family evacuated the car. The car was examined/inspected but the shop, at that time, found no problems. There were no codes and the smoke never returned. Then a month after that, our car had a ‘major drive failure’ warning light, plus it wouldn’t shift properly into gear because of an engine idle condition. I had to have it towed to a BMW shop. The mechanic told me that a fuse had blown, which he replaced. After all of that, we haven’t had any more problems for several months. In my research I have found that wires on a car aren’t supposed to melt and burn because the fuses have a requirement of protecting the circuits. But they say I have to pay for the failed wiring harness and disa valve replacements. What is your assessment of all of this and is there another route I can go to get this problem fixed?

A: Wow! Very disturbing issues to experience, ...

Wow! Very disturbing issues to experience, especially the electrical smoke with your family in the vehicle. Based on what you've told me about you 2998 BMW 740i, this is not going to be a quick one to diagnose and repair. Fuses are designed to protect the wiring and the components on the circuit, though the systems can fail. The wiring insulation can crack, causing bare and exposed wires, which will allow shorts to happen or other wiring damage to occur.

As far as the smoke in the car, it could have been caused by oil being spilled onto the exhaust manifold during an oil change, or steam burning off from a moist engine. Correctly repairing your vehicle will require someone with specific product familiarity, good electrical skills, patience, and the right tooling and service information. If you would like to have this looked at, a certified technician from YourMechanic can come to your car's location to diagnose your electrical issues and perform the appropriate repairs.

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