EDZ649
MB Enthusiast
I think this has already been done.
SL500 (R129) - Cut out & will not start
I think this has already been done.
Hi
The ignition switch has already been replaced but has not cured the problem. It is exactly the same. My next thought is the immobilisor transponder on the ignition barrel that Ian mentioned earlier or the immobilisor system itself or the multifunction relay.
The problem seems to be located between the ignition switch and the starter relay (a direct feed to the starter at the starter relay cranks the engine - although the car still does not start).
The ignition switch has already been replaced but has not cured the problem. It is exactly the same. My next thought is the immobilisor transponder on the ignition barrel that Ian mentioned earlier or the immobilisor system itself or the multifunction relay.
The problem seems to be located between the ignition switch and the starter relay (a direct feed to the starter at the starter relay cranks the engine - although the car still does not start).
Update
Good news is that we got the car started! Bad news is that it only lasted 5 minutes.
There is a relay-type black box that is located behind the diagnostic port under the cover. The purpose of this device is to shut down systems in the event of a power surge, so in this sense it could be seen as a 'surge-protector'. There are 3 fuses located on the top/inside of this box. One of these had blown. The fuse was replaced and it blew instantly, this happened 4 times. On the 5th attempt the fuse did not blow straight away. On turning the ignition key the car started immediately without any fuss or hesitation. It ran for around 5 minutes and then the fuse blew out and the engine cut out. The fuse was replaced and this time it blew immediately, and again, and again.
There is, it would seem, something that is causing this fuse to blow. The problem is that it serves several functions including the cooling fan for the ECU. Now we move on to the next wiring diagram...
Good news is that we got the car started! Bad news is that it only lasted 5 minutes.
There is a relay-type black box that is located behind the diagnostic port under the cover. The purpose of this device is to shut down systems in the event of a power surge, so in this sense it could be seen as a 'surge-protector'. There are 3 fuses located on the top/inside of this box. One of these had blown. The fuse was replaced and it blew instantly, this happened 4 times. On the 5th attempt the fuse did not blow straight away. On turning the ignition key the car started immediately without any fuss or hesitation. It ran for around 5 minutes and then the fuse blew out and the engine cut out. The fuse was replaced and this time it blew immediately, and again, and again.
There is, it would seem, something that is causing this fuse to blow. The problem is that it serves several functions including the cooling fan for the ECU. Now we move on to the next wiring diagram...
That's circuit 15, a 30 amp fuse?
10 amp standard size blade fuse.
Finally! Yes!!
After determining that the surge protector box covers several possible components. We replaced the fuse several more times and then it no longer blew. The car started fine. However 2 issues became immediately apparent.
Firstly there had to be a minutes delay between switching on the ignition and the engine firing. If the key was switched on and then turned to crank immediately - the engine would not start. It had to be left for around a minute for the engine to fire.
Secondly on driving the car it would not shift gear beyond second.
On further investigation and with the help of a wiring diagram and some advice we discovered (via diagnostic connection) that the gearbox ECU was not recognising the shift pattern. When the car was in 'D' or 'R' the ECU would show 'Z'. From this two potential problems were identified.
1. On the automatic gearbox sump/casing there is a multiplug which connects internally to the circuit plate for the gearbox solenoids (not sure if that is the actual name for the part) and externally the wire leads up through the vehicle to a module in the back of the passenger footwell. This is the gearbox ECU.
A visual inspection of the automatic transmission sump showed 'very light' oil residue around the plug and on that corner of the sump. Normally this would be considered 'normal' as there was no obvious sign of a leak.
However it transpires that the seals on this multiplug leak, the consequence of this is that transmission fluid is induced UP (a sort of electromagnetic action) through the wiring harness and into the multiplug for the gearbox ECU and possibly into the ECU itself. (You have to see it to believe it).
In this instance there was transmission fluid on the multiplug and in the footwell but not in the ECU (thankfully!). The remedy was to disconnect the multiplug at the gearbox end and allow as much of the transmission fluid to drain back down through the harness (via gravity). This was aided by using electrical spray to clean the multiplug connections either end.
The auto transmission sump was removed and the seals on the multiplug were then replaced. This alone could not be the cause of the problem so we also replaced the electrical plate/circuit for the gearbox solenoids while the sump was off. The transmission oil, strainer and gasket were also changed.
2. The second problem that was identified, was that there was an issue with the signal being sent by the shift mechanism in the centre console to the gearbox ECU. On removing the centre console it was almost immediately apparent that the multiplug from the main wiring loom had fused itself into the shift control module (to which the shift lever is connected). It was burnt out. The remedy was to replace the shift control module and a new multiplug had to be wired onto the loom. This was quite a task as all the wires on the old plug had fused together and had to be painstakingly seperated in order to ensure the new plug was correctly wired - like for like.
Both problems remedied. All the fault codes were reset (they would not clear previously). The car starts on the button (no delay) and drives like a dream - perfect.
Two things to note. Firstly the problem was not obvious and the wiring diagrams proved invaluable. They showed the connection between the surge protector and the Gearbox ECU. However they were very difficult to obtain (even through purchase) and great thanks goes to a certain indvidual.
Secondly all the parts came from MB directly and they were all available including the kit for rebuilding the multiplugs (otherwise a new loom!).
Happy to have it back!
Last edited:
It should be 30A for circuit 15.
The problem you described is quite common across the range with 722.6 gearboxes. The electro-hydraulic plate was redesigned and a new pilot bushing available to prevent fluid leaking:
I am not sure if the fuse has been replaced before, but we just replaced like for like. You are absolutely right about this being a known problem (except to me! LOL! ). I am not 100% sure if this was the issue with the starting of the car. I suspect it was part of the reason why the car would not shift gears properly.
My gut feel is that the starting issue was initiated by the fusing of the loom to the shift module, thereby causing the fuse to blow and eventually the multiplug had deteriorated to the point of no return. However there was enough of a connection that prevented the fuse from blowing but other connections were deteriorated to the point of preventing the car from performing as it should.
It has been an interesting experience to say the least!
I would like to thank everyone for their input, it is has been a great help not least in concentrating the mind around the problem. I do hope that identifying the issues will be of help to anyone in a similar predicament.
Last edited:
- Joined
- Feb 8, 2007
- Messages
- 20,694
- Location
- Portsmouth, Hampshire.
- Car
- E55K SL500 E250X2 Smart44 Brabus Track car E450Cabriolet X350 Pick up
Whats the problem?
