Just got my new (to me) m400 and have discovered a host of things that need to be addressed. One of the more urgent things is the fuel gauge. When the car is off, the fuel gauge reads 0 (empty). However, when the car is turned on, the fuel gauge immediately jumps to 1+ (extra full). When I took delivery of the car off the transport truck, I noticed to full gas reading and thought to myself - my, how considerate that they filled the tank prior to shipping it. So I drove it around for a day but noticed that the fuel gauge never moved. So I'm thinking that this car either as a 490 gallon tank and that it just hasn't used much fuel or the gauge is broken. Being more suspicious of the latter, and worried that I might be running on fumes, I went to ye olde friendly fuel refilling depot and lo and behold she sucked up 13+ gallons of fuel! BTW, what is the capacity of the fuel tank; how close to fumes was I?

If I had to guess, there are just 3 components to this system. 1) fuel level sensor 2) wiring between sensor and gauge and 3) gauge. Is there anything else? If I had to guess, I'd guess its the sensor that is bad. Has anyone else run across this? What is the troubleshooting algorithm I should follow to diagnosis and correct this?