Fuse Numbers and OBDII Machines

The fuse is likely not the problem (it is a protection element after all). It sounds like the fuse is operating due to a high current fault somewhere after the fuse.

Check your circuit you likely have a fault, and this fault (be it damaged or overloaded equipment, short-circuited wiring, etc) is possibly what is causing your OBDII machine not to read.

While I do not have the answer to your question, perhaps I can help. What is not working in your car? Go through your car, and try to check all functions. Some things you can not test though. Stability control, Anti-lock braking are examples. If this does not give you the answer, try doing a web search. There must be a few MB websites.

Once you can identify what the fuse is protecting, try isolating components of that circuit. The more components that you can eliminate, the easier it will be to find the short.

If the fuse is 40 amps, it must be a high power device. The blower motors used for heater/air conditioning, the radiator cooling fan. The motors used for power seats or power windows but only if they are all grouped together. Does the car have heated seats? You should be thinking of high current systems.

Good luck.