LED Testers

Why they do not perform properly

LED type testers as previously described, are light, compact and very simple in operation. This makes them economical to produce particularly in countries such as China.

But it is worth bearing in mind that they are not produced by specialists who work in the field of towing electrics and this presents the problems in using this type of tester. Add to this that a number of vehicle manufacturers state in their literature that their vehicles are NOT able to tow trailers equipped with LED’s!   This is extremely important when using these types of testers.

Listed below are some of the main reasons why this design will not adequately function:

• LED’s by their design, draw minimal load current when operating. This has the effect that the vehicle being tested is not able to see the lamps on the trailer and this can cause a number of faults.
• The trailer flasher failure function is not able to be tested as the LED testers are not equipped with circuit switch-off facility, or the loads are not sufficient for any installed trailer module to effectively monitor and so once again, a ‘fault’ is generated.
• Earth continuity faults cannot be tested effectively.
• Fog lamp cut-off cannot be tested properly with LED testers. (NOTE:  Fog lamp cut-off is not mandatory in the UK but is within Europe!)
• If the vehicle being tested is equipped with a CANbus based trailer module, this will also generate a fault in the load system as well as a general communication fault as shown on the dash display.

We have shown on the diagram below why LED testers are not satisfactory

 

	With a tester connected,the modern motor vehicle equipped with a trailer module, sends a signal which searches for a ‘resistance’ signal equivalent to a 21W bulb. This resistance needs to be available on a number of lamp circuits. This illustration is using a bulb tester and so the circuit is complete.
	In the case of the LED tester, the vehicle that is equipped with a trailer module, ‘searches’ for a resistance mass as given by a bulb. As an LED functions in a different way to a bulb, there is no such resistance and so the trailer module or the vehicle’s own technology, is not able to respond to ‘detect’ the presence of a trailer and faults are generated.

There is no doubt that the tester provided by Right Connections will effectively test the functions required not only for general MOT requirements but also for towbar installation.