I’m having a problem with my 2001 Mercedes Atego 815 which is that 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’m hoping someone here might have had a similar experience and know what the problem is. 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 if it’s not going to be a solution so I’m hoping to find someone who’s experienced something similar and can offer some advice.
Sounds like a fault on the can bus.
The MR ecu is linked into all the other systems like driver control (FR) suspension (NR) and the main logged ecu INS.
If it keeps losing its MB number(the Mercedes id tag) there is a comm fault in the can ring.
Can only suggest check starter motor connection (dont ask me why)but a corroded power feed sometimes causes memory loss,connections on to engine ecu (like a big scart lead on the block) or low battery voltage when its been stood a few hours which stop the ECUs communicating (can is always live even though they only run at 5 volts) and engine ecu needs re introducing to other can nodes.
It sounds like it could be either an internal battery or capacitor gone bad on the circuit board. They can be repaired if you can find the right electronics whiz.
Thanks for your helpful replies. I will check out the wiring first.
I have found someone who can check and possibly repair the control unit quite reasonably. If that proves successful I’ll post their details.
Hi Justin, Dunno where you are in sussex or even if you live, but if have no joy with electric chap, i know a wizz down in Rye Harbour he is ace with electrics and hydraulics, he will sort you out £35 ph would take him 30 mins to source problem bud.
Check the wiring from the PLD/MR unit on the side of the engine where it goes under the rear of the engine they have a habit of chaffing through at the back of the sump.
As our learned friend suggests it’s more than likely CAN Bus wiring to the FR.
Wagger:
Check the wiring from the PLD/MR unit on the side of the engine where it goes under the rear of the engine they have a habit of chaffing through at the back of the sump.
As our learned friend suggests it’s more than likely CAN Bus wiring to the FR.
The engine management system employed by this engine is the PLD (Pumpe Leitung Duese-German abbr) which incorporates single plug-in pumps for each cylinder supplying fuel under pressure (up to 1,600 bar) to the injection valves. A control unit MR monitors all engine operating conditions via several sensors and varies the injection pressure to suit each operating condition.
Wagger:
I’d have thought you would have known that!!
The engine management system employed by this engine is the PLD (Pumpe Leitung Duese-German abbr) which incorporates single plug-in pumps for each cylinder supplying fuel under pressure (up to 1,600 bar) to the injection valves. A control unit MR monitors all engine operating conditions via several sensors and varies the injection pressure to suit each operating condition.
ah well always thought that the individual pumping elements used the MR ecu to control the opening and closing of the pump dump valves to control the amount of fuel injected.
So does this mean at tickover the fuel is only injected at low pressure?
Never noticed ours smoking due to low atomisation pressure but of course you would know better eh!
PLD lol!
You can have mr control units repaired, not always successful first time but I have worked on one and had it done. I can’t remember where it was done repaired though!
adesoo:
You can have mr control units repaired, not always successful first time but I have worked on one and had it done. I can’t remember where it was done repaired though!
I have had a few done at Alliance in Sheffield, they can repair some faults but not all. I sent them one a few weeks ago with a CAN fault but they couldn’t fix it?
I sent the MR to Autotek in Poole. They seem very friendly and helpful and diagnosed the problem straight away. They’ve found there’s an intermittent power fault on the board caused by a power overload, presumably from using the plasma cutter. Well that was an expensive lesson!
Thanks for all your help on here.
Lost could you message me your electric blokes contact details in Rye. Could be useful in the future, I’m near Shoreham so not too far.