Diagnostics is now an integral part of many Tow Bar installations

When fitting a dedicated vehicle specific tow bar electrical kit you may need to diagnose the vehicle AND update the software.  This informs the vehicle that you have fitted the electrics and activates any safety features relating to towing. 

There are a few different software tools on the market but most of them will access the following functions and make changes to your vehicle if needed after the tow bar wiring installation:
Fog cut out
This switches off the fog light on the tow vehicle when towing a trailer or Caravan.  It stops the glare between the vehicle and the trailer or Caravan.
Lane Assist
The parameters may be changed or in some cases it will be deactivated when towing.
Adaptive Cruise Control
The parameters may be changed or in some cases it will be deactivated when towing.
Parking Assist
In some cases this may be deactivated.  If the vehicle has a manual button on the dash the parking sensors may not be deactivated.
Hill Start
The parameters may be changed to this function.
Boot Opener
When the towing plug is in use the auto boot opener will be deactivated.  This prevents the tailgate from opening and hitting any potential obstruction.
Trailer Stability Control
Some vehicles have this option to be activated when towing.  It will detect any snaking and apply the brakes in a certain sequence to bring the trailer back under control.
Bulb failure
This is a standard feature on all dedicated kits.  The car will double flash if you have an indicator failure on the trailer.
Dynamic Ride Control (DRC)
The parameters are sometimes changed on vehicles fitted with this function while towing.

NOTE: You cannot diagnose universal towing electrics so none of the above features can be activated or deactivated with the universal type of Towing Electrics.