Canbus resistors

[MrJohn91]

Hi Guys,
I purchased some LED fog lights but these don't agree with the canbus system so wanted to fit some resistors, had a little search and purchased these
EBay item 162467048749
Tried but they didn't seem to work. I fitted this as part of the wiring rather then "splicing" it with the clips provided. Does anyone know if this could cause them not to work?

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[Speed-FReek]

Your original H3 incandescent fog light bulbs would have been 12V 55W ones which have a resistance of 2.6 ohms and a current draw of 4.6 amps...

• R = V² / P, so (12 x 12) / 55 = 2.62 ohms
• I = P / V, so 55 / 12 = 4.58 amps

The resistors you have fitted are 6 ohm ones and will be drawing 2 amps of current...

• I = V / R, so 12 / 6 = 2 amps

So the resistors you've fitted may have a resistance and current draw that are outside the tolerances that the CAN BUS uses to check for faulty bulbs.

For 55W bulbs you need to use 3.6 ohm resistors which I believe are the closest you will get in that type of resistor to the resistance of the original 55W incandescent bulbs. A 3.6 ohm resistors that draws 3.3 amps of current.

You can get some here: http://www.hids-direct.co.uk/2-x-100w-3-6ohm-resistor-led-fix-for-55w-bulbs-such-as-h1-h4-h7

Also, ensure that you are wiring them in parallel with the LED bulbs and not in series.

 

[MrJohn91]

Your original H3 incandescent fog light bulbs would have been 12V 55W ones which have a resistance of 2.6 ohms and a current draw of 4.6 amps...

• R = V² / P, so (12 x 12) / 55 = 2.62 ohms
• I = P / V, so 55 / 12 = 4.58 amps

The resistors you have fitted are 6 ohm ones and will be drawing 2 amps of current...

• I = V / R, so 12 / 6 = 2 amps

So the resistors you've fitted may have a resistance and current draw that are outside the tolerances that the CAN BUS uses to check for faulty bulbs.

For 55W bulbs you need to use 3.6 ohm resistors which I believe are the closest you will get in that type of resistor to the resistance of the original 55W incandescent bulbs. A 3.6 ohm resistors that draws 3.3 amps of current.



Also, ensure that you are wiring them in parallel with the LED bulbs and not in series.

You sir are a gentleman and a scholar, thank you very much for a swift reply!
I shall let you know how I get on

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[Speed-FReek]

No probs

Alternatively, try and find someone near to you who has VCP and get them to re-program your BCM with the bulb diagnostics check switched off for any bulb circuits where you have (or want) LED bulbs instead of an incandescent ones. Then you can fit LED bulbs without needing to bother with the correct resistors (or any resistors at all for that matter) because you will never get the bulb check light coming on for any bulb circuits where the bulb diagnostics has been switched off. If you decide to go down this route, just make sure that whoever does it is using a genuine VCP cable and not a clone because this change re-programs memory cells in your BCM and if anything goes wrong while this is being done (which is far more likely with a knock-off cable) then there will be a risk that your BCM could get bricked. Note that this cannot be done with VCDS. It has to be done with VCP or dealer diagnostic tools.

 

[MrJohn91]

No probs

Alternatively, try and find someone near to you who has VCP and get them to re-program your BCM with the bulb diagnostics check switched off for any bulb circuits where you have (or want) LED bulbs instead of an incandescent ones. Then you can fit LED bulbs without needing to bother with the correct resistors (or any resistors at all for that matter) because you will never get the bulb check light coming on for any bulb circuits where the bulb diagnostics has been switched off. If you decide to go down this route, just make sure that whoever does it is using a genuine VCP cable and not a clone because this change re-programs memory cells in your BCM and if anything goes wrong while this is being done (which is far more likely with a knock-off cable) then there will be a risk that your BCM could get bricked. Note that this cannot be done with VCDS. It has to be done with VCP or dealer diagnostic tools.

That sounds like a better idea for me. Now just to find someone near me with VCP!

Sent from my E6853 using Tapatalk

 

[MrJohn91]

Your original H3 incandescent fog light bulbs would have been 12V 55W ones which have a resistance of 2.6 ohms and a current draw of 4.6 amps...

• R = V² / P, so (12 x 12) / 55 = 2.62 ohms
• I = P / V, so 55 / 12 = 4.58 amps

The resistors you have fitted are 6 ohm ones and will be drawing 2 amps of current...

• I = V / R, so 12 / 6 = 2 amps

So the resistors you've fitted may have a resistance and current draw that are outside the tolerances that the CAN BUS uses to check for faulty bulbs.

For 55W bulbs you need to use 3.6 ohm resistors which I believe are the closest you will get in that type of resistor to the resistance of the original 55W incandescent bulbs. A 3.6 ohm resistors that draws 3.3 amps of current.

You can get some here: http://www.hids-direct.co.uk/2-x-100w-3-6ohm-resistor-led-fix-for-55w-bulbs-such-as-h1-h4-h7

Also, ensure that you are wiring them in parallel with the LED bulbs and not in series.

These worked a treat. Thanks very much for your help!!

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