I have a BMW 525i, produced in 2004. The fastest speed now is only 110km/h. Is it because someone set the max speed limit or a problem of the engine? How can I remove the max speed limit as such if not a problem? and how can I fix the problem if it is? Million thanks!

verify spark plugs and ignition colis, scan vehicle also for possible error codes

press the "limit" button on the radio computer. Adjust the peed higher or set to "--" to turn off.

disconnect battery and re connect

If this is not a limit you have set on your indash menu system..try removing the battery negative terminal for 20 min. ** Dont leave your keys in the car or close the boot. When refitting the battery , if possible make sure the side ligts are set to the On position. Dont mess with the battery refitting . put it straight on ..firm!
I f this does not reset the facia info it will require scanning with a quality unit to verify if the fault can be cleared from memory or is a facia unit specialist repair (these do fail .. see BBA-Reman).
Cheers
Roger

check your cruise / speed limiter control
check battery voltage
check crankshaft position sensor

Great to hear that you got a handle on this. So few folks understand there car and it is the 2nd biggest outlay of cash they make in a lifetime.

its going into safe mode which limits the engine output but as to the cause of this i couldnt say ,the thing is the national speed limit here in spain is now 110kms so its still capable of the top limit ,but all joking aside it would need a jaguar diagnosis to find the fault but try disconnecting the battery and joining the leads together for a while say 15mins and see what happens this might reset the ECU for you but other than that then its the dealer diagnostics.I cannot read codes on a europeon model even with a fancy machine that cost me 3000euros ,In fact most vehicles from 2005 i cannot read .

It is very important that the engine not overheat! The head can crack and this would be very bad.
I think your car is too new to need a new radiator.
Make sure the coolant level is correct.
Check the thermostat housing for leaks.
When the engine is hot, check if the fan clutch is locked up and actually driving the fan. Turn the engine off and grab the fan and try to turn it. It should turn stiffly. If it spins freely the fan clutch is dead.
It is possible that the water pump impeller has failed, especially if it is a plastic one.

3 things it could be
1/ is the oil pump is not getting enough oil
2/ the oil is the wrong type for your car as you should be running 20W 40 SHELL.
3/ You have a OPLS(oil pressure light switch) in the engine and that could be faulty.
SO try No 2 first (drain and refill) then try it on a long run if still playing up then let me know Ron

sounds like you have a faulty mass air flow meter.Change it.hope that was helpfull.