Thread: DSC towing problem

Does the car lurch when cornering with the van? Perhaps the shocks are worn-out but check the ball loading and the van loading generally for heavy weights front and rear.

Originally Posted by Graeme

Does the car lurch when cornering with the van? Perhaps the shocks are worn-out but check the ball loading and the van loading generally for heavy weights front and rear.

hi graeme when travelling on winding roads yes the unit does lurch van may be a little overweight but when travelling uphill its in a straight line

Do you see the DSC light coming on when going uphill?

Does the trailer dash light illuminate when you indicate?

Reason why I ask, is that of not then the car is not recognizing the trailer probably because of LED lights not providing enough resistance

This will prevent the car from going into tow mode which affects DSC, gearbox shift patterns etc.

You’ll need one of these (or equivalent) to remedy

LED Tow Connect - Tow LED Fitted Trailers Safely: Discovery 4

Originally Posted by BrianElloy

....... probably because of LED lights not providing enough resistance

Hi,
I suspect the wording should be that the led lights have too much resistance and not providing enough current draw to trigger the 'trailer mode'.
However, when not braking, indicating or using lights, the caravan lighting circuit does not drawer power. So there must be something else to tell the vehicle a trailer/van is being towed.
Someone more knowledgeable than me may be able to explain what is happening.
Cheers

Do you have enough trailer braking engaged? It sounds like the trailer is pushing on the vehicle while it’s turning going downhill and possibly the yawing the vehicle as it senses the load of the trailer and is causing DSC engagement.

Maybe try enabling more trailer brake and see if that changes the car’s attitude and DSC activation. It should not do it.

Originally Posted by austastar

However, when not braking, indicating or using lights, the caravan lighting circuit does not drawer power. So there must be something else to tell the vehicle a trailer/van is being towed.

A D3 pulses the trailer blinker circuits at regular intervals looking for load on the circuits to indicate the presence of a trailer. A D4 pulses the trailer blinker circuits every time the driver's door is closed.

1. You are required by law to have a braked trailer if the trailer mass is in excess of 750kg. You can either have hydraulically braked trailer via the hitch, or the more popular electric brakes, in which case you need an electronic brake controller in the car, either the RedArc or Tekonsha P3 are good examples. These are relatively cheap and easily retrofitted by an autorlectrician or a handy DIYer.

2. The D4 (maybe D3 too) sends a signal down each indicator wire roughly every second or so (could be more often, I can't exactly remember) when towing. If the resistance is high enough (I.e. your trailer lights are or have been on), the car knows it has a trailer attached and adapts the DSC, ESC throttle and braking systems accordingly. it also cancels the reversing sensors and the auto levelling feature of the suspension. Even when driving without lights on, each time you signal, the trailer status is reconfirmed. So when you first hook up and plug in and do your light check, the car knows it has a trailer on.

3.however, the system appears to be designed for incandescent lights, in t that these draw more current than LED, so what a lot of people have experienced is that when towing a trailer with led lights, the car doesn't know it's towing and so the DSC, ESC etc are not modified. This can cause unpredictable handling and the car to fault.

The common solution is to fit load resistors either at the trailer lights, or into the wiring harness for the rear plug. This increases the line load so that the car detects it has a trailer on.

Also check your down load on the hitch at the car, if the van is not correctly loaded or too heavy, you'll have too much downward load, leading to instability when towing, worse downhill.

From memory (others here that have far more knowledge on this than me may be able to help further) I believe you are allowed a max downward load of 10% of the maximum towing capacity, so for D3/D4 this is 350kg.

Hope this helps