I got a Mercedes-Benz axor 2006 model it's not starting display Mr code,but when let it do self check it doesn't display the faulty codes what cud b a problem?

Question edited for clarity full make model.
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Mercedes Benz Fault Codes

Classtrucks.com https://www.classtrucks.com > buyers-guide > mercede... This page covers the most significant information you need to know about Actros truck fault codes, including common codes, their meanings, and methods of fixing

Mercedes Actros GS Fault Codes

Truckmanualshub.com https://truckmanualshub.com > mercedes-actros-gs-fau... List of Gear Shift Fault Codes (GS) for Mercedes-Benz Actros, Axor, Atego; MB Error Codes.

Fault Code List For Base Module (GM) Control Unit 1 ' PDF

Scribd https://www.scribd.com > document > Fault-Code-List-fo... 5643 Windshield washer pump motor has Short circuit to positive. 5644 Windshield washer pump motor has Open circuit. 5742 Headlamp washer pump motor has Short ...
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Question edited for clarity.
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Shown in the link.

https://www.google.com/search?q=MR+7708+code+Proportional+valve+row+1+has+a+short+to+ground

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We don't deal with Truck / Lorry Tractor units or 'selfie 0 gears', but ....

https://www.google.com/search?q=axor+2543+gs+clutch+failure+symptoms

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This code is showing a transmission problem. Your best option is to take the vehicle to a transmission specialist. If you don't know what you are doing gearbox mistakes are VERY expensive to sort out.

see the link and scroll down the page
https://www.pdfmanual4trucks.com/mercedes-benz/

that is not a sensible thing to do on a diesel as it will just keep revving until it destroys its self , if its more power etc you want then a good service and a fuel addative would be much more advisable

air filter may b blocked

The MR code comes up because you are not allowing the vehicle to do the self checks before trying to start engine, it therefore does not regognise the key in the ignition and the immobiliser is activated. to overcome this allow the vehicle to do its self checks and when the neutral N symbol is shown then turn ignition switch to start.