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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 538
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Mercedes 815 Atego MR unit losing data

Customer Question

I’m having a problem with my 2001 Mercedes Atego 815 based motorhome.

The MR engine control unit intermittently fails to load stored data such as engine no. and cylinder pump no.’s. As a result the MR unit is not communicating with the FR unit and although the vehicle starts it is in emergency running mode i.e. the engine runs but the accelerator pedal does not work.

If you try stopping and starting the engine numerous times it will randomly load the required data causing it to eventually start and respond to the accelerator normally.

I have had a Mercedes mechanic spend 7 hours trying to solve this. He has the full star diagnostic equipment.

No errors are shown and the initial quick test gives a tick against FR and MR controls. It is only when you dig deeper into the parameters that you discover the missing engine no etc. Re-entering these corrects the problem in the same way that starting and stopping the engine numerous times does but the data then gets lost again. This can be anything up to a few days later.

He thinks it’s likely that the MR unit is faulty probably due to a power spike when a friend did some work on it with a plasma cutter shortly after I bought the vehicle. But he is not absolutely certain of this.

My feeling is that if the unit was damaged in this way then the fault would not be intermittent and if there were a physical defect with the MR unit, it would show up as a fault in the initial diagnosis log.

Replacing the MR unit is a very costly experiment so I want to be certain that is the solution before doing so.




Submitted: 3 years ago.
Category: Mercedes
Expert:  Shantal-Mod replied 3 years ago.
Hello Justin,

I'm Shantal and I'm a moderator for this topic.

We have been working with the Experts to try to help you with your question. Sometimes it may take a bit of time to find the right fit.

I was checking to see if you had already found your answer or if you still need assistance from one of the Experts.

Please let me know if you wish to continue waiting or if you would like for us to close your question?

Thank you,

Customer: replied 3 years ago.

Hi Shantal,


I've not had an answer from here yet and I have now had some useful information from other forums which may help me solve the problem.


By closing the question do I automatically get a refund of the £27 paid.