S212 E350 Limp mode when towing

[JAM60]

MY 2013 350 AMG/Sport Est has developed an intermittent (once every 200miles) fault when towing our large caravan. It appears when the caravan seems to tug the car backwards on the motorway. The safety system inop message comes up and goes in to limp mode. Stop & restart and all ok for another 200 miles or so? There are no codes logged? Tried switching srs system off but alas it still did it. I do occaisionally drop it down through the gears and hold it at higher revs during trips in case it was EGR/DPF related. No luck Love the car but going to have to consider another tow barge if I cant sort it. The tow bar was fitted by a specialist although He has fitted loads before.

 

[BTB 500]

It appears when the caravan seems to tug the car backwards on the motorway

Are you sure it's not an issue with the caravan ... does it have AL-KO ATC? That activates the caravan brakes if swaying is detected, and maybe the car is reacting to that.

Is this a single or twin axle caravan, and what's the MTPLM? What's the car's plated towing capacity? How long have you been using this combination?

 

[toteimerced]

Has the car been remapped, if done badly, the excessive fuel pressure can put the car into limp, under load.

 

[JAM60]

Are you sure it's not an issue with the caravan ... does it have AL-KO ATC? That activates the caravan brakes if swaying is detected, and maybe the car is reacting to that.

Is this a single or twin axle caravan, and what's the MTPLM? What's the car's plated towing capacity? How long have you been using this combination?

Hi BTB 500,
That was my assumption as the caravan does have ALKO ATC. Hence I deactivated srs via the onboard screen. The caravan is 1803kgs twin axle and the car spec says 2100kg capacity but it is running about 92% which is not ideal. It is a new tow car as I previously towed with large SUV's. I have improved it massively by careful loading, as the caravan bossed the car. However I love the car but would like the limp mode issue resolving.

 

[JAM60]

Has the car been remapped, if done badly, the excessive fuel pressure can put the car into limp, under load.

Hi and thank you I understand your comment but solo the car is 100%. & its only when towing. When towing the power is brilliant.

 

[BTB 500]

Hi BTB 500,
That was my assumption as the caravan does have ALKO ATC. Hence I deactivated srs via the onboard screen. The caravan is 1803kgs twin axle and the car spec says 2100kg capacity but it is running about 92% which is not ideal. It is a new tow car as I previously towed with large SUV's.

Isn't SRS the airbag/seatbelt system?!

A twin axle is intrinsically more stable than a single so it *should* be ok even at a fairly high match percentage. Quite apart from the limp mode thing you don't want ATC activating other than very occasionally as it will kill the brakes (in 12 months mine wore a set of pads to the point where one drum was scored and had to be replaced, and I never felt it cutting in at all).

What about tyre pressures (both car & caravan)? Are there recommendations for towing in the car handbook - some specify increasing the tyre pressures to the maximum plated ones (full load/high speed) ... this increases resistance to sideways loads.

I have improved it massively by careful loading, as the caravan bossed the car.

OK so I assume you have a decent noseweight and any heavy objects in the centre. You don't have a bicycle rack on the back of the caravan do you? Is there anything you can carry in the car rather than the caravan (thinking of awning etc.)? Have you checked the actual weight of the caravan as it's very easy to accidentally over load.

 

[BTB 500]

Have you checked the actual weight of the caravan as it's very easy to accidentally over load.

Forgot to say ... which might not have caused any obvious issues when towing with a bigger/heavier vehicle.

 

[tonysmb]

It does sound as if the caravan might be applying its brakes and the 'pull' is then confusing the car's safety systems, possibly causing the limp mode, although I can't think why '200 miles' would be a factor. Did you mean ESP and not SRS?

When the towbar was fitted, was the car 'coded' accordingly?; as far as I'm aware that's what MB do but I'm not sure at what age car it was applicable. Some say it's necessary, others not. Technology, eh