Two problems related to power train have been reported for the 2004 BMW 525. The most recently reported issues are listed below.
I was driving on my way to work and started smelling something burning. All electrical warning lights started lighting up the dash and then displays go blank. Passenger compartment was filling up with smoke coming from under glove box. I pulled over and called fire department. We disconnected battery and took to BMW. They said micro-processor located in spare tire storage area had shorted out due to water. I don't carry coolers and don't leave my trunk open when it rains. How did water get there. Bulletins show that sunroof drains get clogged and water gets into trunk and shorts out electrical. Service bulletin says if this happens, customer pay but move electrical to where it can't get wet. So BMW knows it's a problem and can cause a fire but doesn't care to cover repair. Now I'm stuck with $1000 repair for micro-processor just to be able to tell what else is burned up. I have to pay before I will know if it will cost an additional $5,000 to repair. I'm lucky electrical didn't catch fire and burn up entire car.
I own a 2004 BMW 525i with 119,000 miles on the engine. I experienced my car making a thump sound and then the I would lose acceleration. I called the mechanic and they could not find the problem because it did not show the dash errors. This had been going on for 3 weeks and then the mechanic told me my transmission needed replacing. I am disappointed that this is a common problem and nothing is being done about this. I will never buy a BMW again.