Fitted LED rear lights, now getting a 'brake light' canbus err

[ictguy]

OK, so bought these off ebay - http://www.ebay.co.uk/itm/301445755416?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Fitted them to my '04 Cayenne. All lights work but I am getting a 'check brake light' canbus error when I first apply the brakes. The exclamation mark then remains on.

Does anybody know how I can fool the system into thinking the brake lights are working??

Thanks

[JFP in PA]

OK, so bought these off ebay - http://www.ebay.co.uk/itm/301445755416?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Fitted them to my '04 Cayenne. All lights work but I am getting a 'check brake light' canbus error when I first apply the brakes. The exclamation mark then remains on.

Does anybody know how I can fool the system into thinking the brake lights are working??

Thanks

 

Quite often, putting LED lights on a vehicle that was not so equipped from the factory results in error codes because the LED's do no exhibit the same circuit resistance as the OEM lights, making the system think a bulb is burned out.  this can usually be overcome by adding the correct type of resistor to the electrical circuit.

[ictguy]

Thanks for the quick reply. I am not getting a 'rear light error' when I switch the lights on, only the 'brake light error'. Even though both are made up of LED's, which leads me to think they have been manufactured with the incorrect resistance on the brake light circuit. Does anybody know what resistance is required to prevent the error? Thanks.

PS. The double posting was an error, my iPad hung and I pressed the 'submit post' button twice.

Edited May 30, 2015 by ictguy

[JFP in PA]

Thanks for the quick reply. I am not getting a 'rear light error' when I switch the lights on, only the 'brake light error'. Even though both are made up of LED's, which leads me to think they have been manufactured with the incorrect resistance on the brake light circuit. Does anybody know what resistance is required to prevent the error? Thanks.

PS. The double posting was an error, my iPad hung and I pressed the 'submit post' button twice.

 

LED's have very little internal resistance, which is why they are so bright on the same voltage; some manufacturer's of aftermarket kits offer add on resistor kits specifically to address this problem.  The reason you get the error on the brake lights is they are a mandated safety system, so they are monitored.

 

I'd suggest contacting the manufacturer and see if they offer a kit for this issue.

[ictguy]

Thanks, I will contact the suppliers of the unit. Surprised it doesn't have a load resistor built in though. Do you think this would help if I could break the wiring and put it in? http://pages.ebay.com/link/?nav=item.view&alt=web&id=261170139838

[JFP in PA]

Thanks, I will contact the suppliers of the unit. Surprised it doesn't have a load resistor built in though. Do you think this would help if I could break the wiring and put it in? http://pages.ebay.com/link/?nav=item.view&alt=web&id=261170139838

 

I have no idea if that would help.

[ictguy]

Is it possible to make the checking of the brake lights inactive in the canbus system? Is there a device I could purchase to change these settings? Thanks for your support.

[JFP in PA]

Is it possible to make the checking of the brake lights inactive in the canbus system? Is there a device I could purchase to change these settings? Thanks for your support.

 

That would probably require some elaborate reprogramming, which would not be easy, and becomes questionable from a liability standpoint as you are involving mandated safety systems.

[ictguy]

Is it possible to make the checking of the brake lights inactive in the canbus system? Is there a device I could purchase to change these settings? Thanks for your support.

 

That would probably require some elaborate reprogramming, which would not be easy, and becomes questionable from a liability standpoint as you are involving mandated safety systems.

Surely no different to putting a load resister across the LED though? Effectively fooling the canbus into thinking there is a filament bulb in place.

Do you know if the left/right brake lights are monitored separately or is the message I am getting because either/both are 'out'?

[JFP in PA]

 

 

Is it possible to make the checking of the brake lights inactive in the canbus system? Is there a device I could purchase to change these settings? Thanks for your support.

 

That would probably require some elaborate reprogramming, which would not be easy, and becomes questionable from a liability standpoint as you are involving mandated safety systems.

Surely no different to putting a load resister across the LED though? Effectively fooling the canbus into thinking there is a filament bulb in place.

Do you know if the left/right brake lights are monitored separately or is the message I am getting because either/both are 'out'?

 

 

You are correct concerning adding a resistor to the light circuits, but it needs to match the LED to the factory light's resistance.

 

I do not believe they are monitored separately, as you get the same indication if one or both are out.

[ictguy]

Thanks, I will measure the resistNce across the LED's and add one in parallel to them to match the resistance of the 21Watt bulb.

I remember that 1/R = 1/R1 + 1/R2

[Ahsai]

Note that you can't use a multimeter to measure the resistance of the LED light directly as it's not a pure resistive load. You will need to measure the current it draws and then derive its resistance.

Most people just wire a 8 ohm 50w load resistor to each light in parallel and that should solve the problem. It's a good approximation because each LED light draws a lot less than 21w.

http://www.ebay.com/itm/2X-50W-8Ohm-LED-Load-Resistor-Blinker-Turn-Signal-Light-Bulb-Fix-Hyper-Flash-/371304409490?hash=item567377a992&vxp=mtr

Edited May 31, 2015 by Ahsai

[ictguy]

Thanks Ahsai, good point. I will buy these ones (UK based company) - http://pages.ebay.com/link/?nav=item.view&alt=web&id=310224122296

Doesn't say 8ohms, but does mention in place of a 21W bulb, so bound to be close. Would have preferred 2 25W resistors in series to help dissipate the heat, but I won't be on the brakes for too long and will mount these to the metal bodywork behind the tail light unit.

[Ahsai]

Yup, they look like the same type. They should work.

[ictguy]

All fixed with the resistors!

[Ahsai]

:thumbup: