Limp Mode no warning lights

[MJSavin]

Hi, I have a 2009 350CLS cdi that upon hard acceleration (especially if it has been restarted after going to the store etc) will shut itself off (like traction control but harsher and without the warning light) if done twice it will go into limp mode, it almost seems like an overboost shut off but there are no warning lights and it resets after being restarted. This is particularly annoying when I stop at a service station on the motorway and after filling up etc I try to accelerate to rejoin traffic only to have it go into car go into limp mode and be stuck at 60mph until I can pull over and restart.
When it goes into limp mode but does not illuminate any warning lights and resets back to normal once restarted. If driven gently there are no issues and the car runs fine.
Any suggestions/help would be really appreciated, I love my car but this is driving me crazy

 

[DSM10000]

Get the codes read and preferably by someone with Star. Not all such faults trigger a warning light.

There are many potential causes from a sensor to a sticking vanes on the turbo, do not guess, get a proper diagnosis and go from there

 

[OneForTheRoad]

It can take around 6 times for a fault to occur to throw the eml. There will be codes stored now however. Exhaust back pressure sensor is a usual suspect or the turbo actuator sticking.

 

[GaugeBoson]

Over the past two years that I have owned my E280, I have had three separate faults which have caused the dreaded limp home mode; each time, it was heavy acceleration that precipitated the limp home condition and there was no EML. In case it helps, this is what my three separate faults were:

1. Turbo actuator: within a week of buying the car I got limp home several times on the motorway. The fault codes were for over-boost and back pressure, but the back pressure fault was apparently caused by the over-boost. The actuator was replaced and all was well again. This was done under warranty, but I believe the reconditioned actuators can be purchased on eBay for around £100.

2. Swirl flap motor: exactly the same problem as in 1 above and the fault code pointed to the actuator again; the indy garage replaced the actuator in case the previous one they fitted was faulty but that did not solve the issue, and they said that a problem with the swirl flap motor causes the same code. I unplugged the swirl flap motor connector and fitted the 'resistor trick'; that five minute job costing 12p solved the issue.

3. Leaking intercooler hose: just a few weeks ago, I got the dreaded limp home mode again; this time I tried turbo cleaner and, if anything, it made limp home mode more frequent. This time there was a mix of both over and under-boost codes; thanks to posts on this forum, I checked the integrity of the turbo hoses and found that the hose running from the intercooler to the inlet manifold has several long splits in it, so I replaced the hose (£70 Mercedes part) and all is good again.

If the codes point to over/under-boost I would inspect your intercooler hoses first (costs nothing), then try the resistor trick (costs pennies and you can search the forum here to find out how) and then finally I would chuck in some turbo cleaner. If none of that helps, then it may be worth trying a replacement turbo actuator.