Canbus

znww5

Active Member
Mar 27, 2011
146
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Thanks for the replies guys - the thing that also puzzled me was the fact that the bulb failure light doesn't come on during the 'bulb test' at start-up. Sounds like a case of 'computer says no' :)
 

MrTSI

Guest
im a little confused with this canbus thing.......... Im looking to change my current bulbs, the H7 dipped beam and the sides 501, and i dont know if it is canbus or not. I was looking for Phillips diamond vision 5000K

any help? :confused:
 

Nutkin

Pop-a-Keg ya?
Aug 24, 2006
2,581
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Schnaitsee
I used to design CANBUS in cars for a living, The easiest way to understand it would be to think of a twitter network for your car, with each module having an account to shout things out.

The headlamps will be controlled by the BCM (body control module) or they might have a separate Headlamp control module (HCM).

This will supply power to the lights and monitor what current they use to ascertain if it is healthy or not. On start up it will just pulse a signal to confirm the loop is connected, IE just make sure a bulb is there. When the lights are on and stable, it will monitor current going through each bulb and if it detects the current draw is out of normal range it will flash up a warning.

There is no such thing as a CANbus bulb etc or anything like that, all that happens is LEDs use a lot less current than normal filament bulbs, so to the module who is looking for a normal resistance from a filament bulb it thinks it has short circuited and is now faulty as very little current is drawn and so sends a message saying Cluster please light up the bulb warning light.

The error free bulbs just have resistors stuck on them to boost the current drawn and trick the Module into thinking the bulbs are good.

the cluster sees this message and does so.

CAN has been going on most cars since pre 2005 and is now industry standard although there are a few other networks in your car such as LIN nodes and sometimes Ethernet/fiber optic.

If you have any questions ill be happy to answer them.
 
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Nutkin

Pop-a-Keg ya?
Aug 24, 2006
2,581
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Schnaitsee
im a little confused with this canbus thing.......... Im looking to change my current bulbs, the H7 dipped beam and the sides 501, and i dont know if it is canbus or not. I was looking for Phillips diamond vision 5000K

any help? :confused:


you will be fine :)
 
Feb 8, 2011
743
1
all that happens is LEDs use a lot less current than normal filament bulbs, so to the module who is looking for a normal resistance from a filament bulb it thinks it has short circuited and is now faulty as very little current is drawn

Open circuit not short
 

Nutkin

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Aug 24, 2006
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No it is short. As a low current represents the filiment welding to itself short and has less resistance.

If it was open then it would come up at the start up check ;)
 

phil750

Active Member
Jul 24, 2012
213
1
My understanding on CANBUS is in fact it is not the wiring itself (it just runs on normal wires) but CANBUS is infact the protocol which runs ontop of them wires.

Did a lot of stuff at uni about it and programming stuff to do with CANBUS , more how it works then how it is used.

But i now it is used in most trucks, and is filtering it way down into cars.

The point being, if its is/not checking certain lights for errors, it should be able to changed as it effectivly software based. on vag.com or something like that?

Might be getting wrong end of the stick though as im a computer guy and now very little about cars!

I can go into a much more indepth description of CANBUS if someone wants it and what it actually does and how it differs from most other protocols.
 

Nutkin

Pop-a-Keg ya?
Aug 24, 2006
2,581
0
Schnaitsee
My understanding on CANBUS is in fact it is not the wiring itself (it just runs on normal wires) but CANBUS is infact the protocol which runs ontop of them wires.

Did a lot of stuff at uni about it and programming stuff to do with CANBUS , more how it works then how it is used.

But i now it is used in most trucks, and is filtering it way down into cars.

The point being, if its is/not checking certain lights for errors, it should be able to changed as it effectivly software based. on vag.com or something like that?

Might be getting wrong end of the stick though as im a computer guy and now very little about cars!

I can go into a much more indepth description of CANBUS if someone wants it and what it actually does and how it differs from most other protocols.


The wires have to be wired in a loop for it to work and certain modules run on nodes. The canbus is the wire system and protocol, The light checking is not really anything to do with CANbus, but more the software on the bcm or hcm.
 

Nutkin

Pop-a-Keg ya?
Aug 24, 2006
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Schnaitsee
I turned off error checking for the sidelights in VAGCOM but the error still came up.
My ECU tends to ignore a lot of my VAGCOM settings, and I have the genuine RossTech lead!

You might be in the wrong module and also it might default the settings when the car is switched on based on a car configuration file present.
 

MrTSI

Guest
so im going to get a regular H7 with no canbus but how about the parking lights (501/w5w)?
 
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