S205 C250 Towbar Electrics

Myk82

New Member
Joined
Jun 23, 2022
Messages
11
Location
Edinburgh
Car
C Class Estate S205 C250 AMG Line Premium Plus
Afternoon,
First time posting on here. Yesterday I took delivery of a 15 Plate S205 C250 diesel AMG Line, Premium Plus. Lovely car with low millage.

I am looking around for option for fitting a towbar, I think I have narrowed down the detachable towbar I am looking to have fitted. However I am not confused around the electrics.

I have read on google the c class can either be fitted with a universal loom with a bypass relay or a car specific loom but this apparantly needs coding by MB to disable the parking sensors when the electrics are connected.

My question is.

If the car specific loom is fitted but not coded, will this still work. And/Or what issues will be faced.

Has anyone had there car re coded by MB for this trailer plug, or can this be done by an independent?

Many thanks

Mike
 

ernie

Active Member
Joined
Apr 3, 2006
Messages
625
Location
Scotland East
Car
Audi Q2; W205 Sport 2018 (Gone)
Afternoon,
First time posting on here. Yesterday I took delivery of a 15 Plate S205 C250 diesel AMG Line, Premium Plus. Lovely car with low millage.

I am looking around for option for fitting a towbar, I think I have narrowed down the detachable towbar I am looking to have fitted. However I am not confused around the electrics.

I have read on google the c class can either be fitted with a universal loom with a bypass relay or a car specific loom but this apparantly needs coding by MB to disable the parking sensors when the electrics are connected.

My question is.

If the car specific loom is fitted but not coded, will this still work. And/Or what issues will be faced.

Has anyone had there car re coded by MB for this trailer plug, or can this be done by an independent?

Many thanks

Mike
Hi Mike,
If you're having it fitted by a towbar specialist, they should be able to code the model-specific electrics as part of the job. An Indy should also be able to do this if you fit the towbar yourself. By the way, MB will charge you an hour's labour for coding, about £160!

As you say, coding disables the rear sensors, so they don't beep continuously while reversing but it also adjusts the engine management map - I'm not exactly sure by how much, but it certainly prevents using the ECO mode while towing. Coding also gives you a complete dashboard warning for any trailer bulbs out.

Just one word of warning...make sure the towbar kit is EXACTLY the correct kit for your car because if the ball extends too far, that may still interfere with the sensors. Also there are kits available that can be fitted to the AMG Line models without having to cut the bumper- Tow-Trust manufactures one such.

Ernie
 

ernie

Active Member
Joined
Apr 3, 2006
Messages
625
Location
Scotland East
Car
Audi Q2; W205 Sport 2018 (Gone)
Afternoon,
First time posting on here. Yesterday I took delivery of a 15 Plate S205 C250 diesel AMG Line, Premium Plus. Lovely car with low millage.

I am looking around for option for fitting a towbar, I think I have narrowed down the detachable towbar I am looking to have fitted. However I am not confused around the electrics.

I have read on google the c class can either be fitted with a universal loom with a bypass relay or a car specific loom but this apparantly needs coding by MB to disable the parking sensors when the electrics are connected.

My question is.

If the car specific loom is fitted but not coded, will this still work. And/Or what issues will be faced.

Has anyone had there car re coded by MB for this trailer plug, or can this be done by an independent?

Many thanks

Mike
Sorry, Mike, should have welcome you to the forum! Trust your new car lives up to expectations.

Ernie
 
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Myk82

New Member
Joined
Jun 23, 2022
Messages
11
Location
Edinburgh
Car
C Class Estate S205 C250 AMG Line Premium Plus
T
Hi Mike,
If you're having it fitted by a towbar specialist, they should be able to code the model-specific electrics as part of the job. An Indy should also be able to do this if you fit the towbar yourself. By the way, MB will charge you an hour's labour for coding, about £160!

As you say, coding disables the rear sensors, so they don't beep continuously while reversing but it also adjusts the engine management map - I'm not exactly sure by how much, but it certainly prevents using the ECO mode while towing. Coding also gives you a complete dashboard warning for any trailer bulbs out.

Just one word of warning...make sure the towbar kit is EXACTLY the correct kit for your car because if the ball extends too far, that may still interfere with the sensors. Also there are kits available that can be fitted to the AMG Line models without having to cut the bumper- Tow-Trust manufactures one such.

Ernie
Thanks Ernie.

Yee I am looking at the Tow Trust one that does not need a bumper cut and will not distract the look when the towbar is not fitted. Planning to fit this myself as I have done a few in the past, but I was just checking the electronics side as each car is differnt and to save splicing the loom I wanted to use the model specific plugs.

I am only going to be using it for a bike carrier. Maybe 2-3 times a month (if that) and not pulling a trailer or caravan. So the mapping/Eco mode will not be an issue. but obviously the parking sensors would be good to get disabled.

I have called MB this morning and they said they fit towbars at a cost of £1700-£3000. i almost fell of my seat. I will instead call the 2 local indy garages and see if they can code the car or just live with the sensors not working for the time I use it.

Mike
 

ernie

Active Member
Joined
Apr 3, 2006
Messages
625
Location
Scotland East
Car
Audi Q2; W205 Sport 2018 (Gone)
T

Thanks Ernie.

Yee I am looking at the Tow Trust one that does not need a bumper cut and will not distract the look when the towbar is not fitted. Planning to fit this myself as I have done a few in the past, but I was just checking the electronics side as each car is differnt and to save splicing the loom I wanted to use the model specific plugs.

I am only going to be using it for a bike carrier. Maybe 2-3 times a month (if that) and not pulling a trailer or caravan. So the mapping/Eco mode will not be an issue. but obviously the parking sensors would be good to get disabled.

I have called MB this morning and they said they fit towbars at a cost of £1700-£3000. i almost fell of my seat. I will instead call the 2 local indy garages and see if they can code the car or just live with the sensors not working for the time I use it.

Mike
Yes, Edinburgh MB quoted me in excess of 2k. However, the MB job includes upgrading the cooling system on the basis that you might be towing up to the car's limit. I think there is also an upgraded wiring loom that needs trim dismantling front to rear.

I had mine fitted by Mr Towbar in Ayr (£850 incl coding) by recommendation of someone in the 'trade'. At NB rates, time costs quickly escalate!

Ernie
 
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Myk82

New Member
Joined
Jun 23, 2022
Messages
11
Location
Edinburgh
Car
C Class Estate S205 C250 AMG Line Premium Plus
Has anyone installed the universal one with the relay. Is it fairly straightforward
 

ernie

Active Member
Joined
Apr 3, 2006
Messages
625
Location
Scotland East
Car
Audi Q2; W205 Sport 2018 (Gone)
Has anyone installed the universal one with the relay. Is it fairly straightforward
I haven't done that. However, you are right to avoid splicing the loom as your car has LED rear lights and the existing wiring wouldn't take the loading of filament bulbs on the bike rack possibly giving rise to dash warnings.
You could check the operation of the relay, but I think it only protects the car and caravan charging circuits which won't apply in your case.

Ernie
 
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Myk82

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Joined
Jun 23, 2022
Messages
11
Location
Edinburgh
Car
C Class Estate S205 C250 AMG Line Premium Plus
Cool.
Going to call pf jones tomorrow as they have a loom to fit the car. But it states it will either

I. No Dealer Download required: Kit will perform full light functions without dealer recode.
II. Dealer Download Optional: Kit will perform full light functions, but will need dealer recode for disabling rear parking sensors & switch on visual warning device.
III. Dealer Download Compulsory: Kit will need a dealer recode for all functions, lights and safety features.

But does not tell you what one it will do. Hopefully 1 or 2.
 

Justintyme

Active Member
Joined
Feb 3, 2018
Messages
988
Location
Ireland
Car
Mercedes Benz w212 E Class
Has anyone installed the universal one with the relay. Is it fairly straightforward
Welcome Myk82. I've installed several towbars down through the years on my own cars, and until the arrival of the HiTeck computerized electrics, it was a pretty straightforward job fitting and wiring a towbar using a universal relay. And to a large extent, its still pretty much doable even now. Basically, the universal relay is a completely separate system that takes a "trigger" from the existing wiring, and independently feeds power to the selected function on the trailer. The relay itself is independently powered and fused ,so has absolutely nothing to do with the existing electrics in terms of supplying power to the relevant bulb on the trailer. Say you put on the left turn indicator, then the cable supplying that power to the bulb on the car, also acts as a trigger to the relay, to switch power to the left turn line on the trailer. And now we come to LED lights, where the universal relay will work very well too, except for the brake light's....... with computer controlled lights, both park and brake lights are fed by a single cable, which works by sending / changing the pulse or width to the led causing it to glow brighter when the brake is pressed. There are so called "Smart" universal relays which are supposed to identify when the brake is pressed, and send normal current to the brake light in the trailer. But I have not yet found one smart enough to work the brakelights in my 2014 E class w3212. So had to resort to taking a separate brake feed from the 3rd brake light set in the rear window. So Myk82, I d be very interested in seeing which type you will have fitted, and how it worked out for you.
**** I should add that I use the trailer quite a lot, but not for seriously heavy towing...caravans, boats etc, that would require modified radiator cooling capacity, and neither did I have it coded. None the less, it works out very well for me."""
 

JHS

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Joined
Sep 8, 2020
Messages
505
Location
Lincolnshire, near Skegvegas.
Car
S205 Estate
Hi Mike,
If you're having it fitted by a towbar specialist, they should be able to code the model-specific electrics as part of the job. An Indy should also be able to do this if you fit the towbar yourself. By the way, MB will charge you an hour's labour for coding, about £160!

As you say, coding disables the rear sensors, so they don't beep continuously while reversing but it also adjusts the engine management map - I'm not exactly sure by how much, but it certainly prevents using the ECO mode while towing. Coding also gives you a complete dashboard warning for any trailer bulbs out.

Just one word of warning...make sure the towbar kit is EXACTLY the correct kit for your car because if the ball extends too far, that may still interfere with the sensors. Also there are kits available that can be fitted to the AMG Line models without having to cut the bumper- Tow-Trust manufactures one such.

Ernie
I had a Tow Trust detachable fitted to my C250d AMG LINE S205 premium plus. It is a specific kit with dedicated electrics. Coded by the fitter. Works flawlessly. A blown brake bulb gave a dashboard warning as soon as I switched on. Highly recommend Tow Sure.
BTW I tow in Eco mode without problems. Not sure why it would be disabled? My cooling system is also OEM and I have no problem in hot weather towing my Eriba Triton 1200Kg.
 
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Myk82

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Jun 23, 2022
Messages
11
Location
Edinburgh
Car
C Class Estate S205 C250 AMG Line Premium Plus
I called a few places today to see if I can get the car coded. But appears to be the hardest thing to get done on its own. Even MB never called me back.

Called a local fitter to me and they said they can fit a detachable with no bumper cut (my main aim) and dedicated loom and code the car. So will take to them. Will save me the hassle and they do it all the time.
 

ernie

Active Member
Joined
Apr 3, 2006
Messages
625
Location
Scotland East
Car
Audi Q2; W205 Sport 2018 (Gone)
I had a Tow Trust detachable fitted to my C250d AMG LINE S205 premium plus. It is a specific kit with dedicated electrics. Coded by the fitter. Works flawlessly. A blown brake bulb gave a dashboard warning as soon as I switched on. Highly recommend Tow Sure.
BTW I tow in Eco mode without problems. Not sure why it would be disabled? My cooling system is also OEM and I have no problem in hot weather towing my Eriba Triton 1200Kg.
I don't have the car now, but from what I remember, in the ECO mode, the car will go into GLIDE Mode when you lift off and effectively the car free-wheels until you brake or accelerate at which point the gearbox selects a gear for engine braking (or accelerating)

It is this part of ECO Mode that was disabled when plugged into a trailer which seems to make sense if you're towing a caravan.

As you say, the Tow Trust system works perfectly, apart from the tow ball catching the parking sensors if the tow ball cover was fitted.


Ernie
 
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Myk82

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Jun 23, 2022
Messages
11
Location
Edinburgh
Car
C Class Estate S205 C250 AMG Line Premium Plus
Ended up getting a detachable Towbar fitted at home (mobile technician) along with dedicated electrics. All in for £650

No bumper cut on my amg line kit.

Super happy with the job.

Definitely recommend Towbar express and there techs.
 

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