Motoring Discussion > CANBUS wiring: How does it work? Miscellaneous
Thread Author: Baz Replies: 42

 CANBUS wiring: How does it work? - Baz
Can anyone explain in laymans terms what this is all about and what it means in practical terms for DIYers? I am reasonably competent on 12v electrics on older stuff but confess to knowing little of this -despite its use in all modern vehicles! Have read a bit on the net but still can't really visualise this. Any experts care to have a go?
 CANBUS wiring: How does it work? - Zero
Its basically a computer to computer communication link with the electrical systems basically broken down into functional units.

Lets take side lights for example.

You want to turn on the lights? In the old days 12v would be provided to your light switch, your switch would then switch this 12v through to the front and rear side lights (possibly through a relay) You have 4 main power wires to the 4 side lights.

These days the lighting controller takes charge of the light. The light switch is just connecting one of the control pins of the lighting controller to earth. You press the button and signal the controller to turn on the lights. The lighting controller will tell the rear lighting controller (over the can bus) to apply power to the appropriate rear lighting cluster taking power from the single 12V rear power ring main.

This of course allows the system to be operated by the environmental light sensors, to turn on lights automatically when its dark. The lighting control is also talking over the can bus to the system that controls the wipers, so if the wipers are on full, it could turn on the lights.

This of course could be linked to the intelligent battery charging system telling it to put more power into the battery, and of course signal the engine controller to up the idle speed a tad due to the increased electrical load.


Basically its to reduce all the thick current carrying cables down to a minimum, replace them with a single signal cable, and be able to control all aspects of what the car is doing.
 CANBUS wiring: How does it work? - R.P.
Thanks Zero - I sort of knew that ! But that was very illuminating


Explains why there's a slight delay in CANbus cars when you turn the lights on or sound the horn !
 CANBUS wiring: How does it work? - Zero
>> Thanks Zero - I sort of knew that ! But that was very illuminating
>>
>>
>> Explains why there's a slight delay in CANbus cars when you turn the lights on
>> or sound the horn !

Its checking to see if you meet all of the "allowed to sound horn" criteria from the rest of the car.
 CANBUS wiring: How does it work? - Baz
Indeed, thanks Z, best explanation I've read, does that mean then that if I wanted to fit a set of cheapo reversing sensors, which apparently take the 12v feed off a reversing light, that the power drain could confuse the relevant controller? Maybe I won't bother!
 CANBUS wiring: How does it work? - Zero
>> Indeed, thanks Z, best explanation I've read, does that mean then that if I wanted
>> to fit a set of cheapo reversing sensors, which apparently take the 12v feed off
>> a reversing light, that the power drain could confuse the relevant controller? Maybe I won't
>> bother!

Yes that is entirely possible, and you may have to purchase an approved makers after market kit.

It also causes a shedload of agro when fitting tow bar electrical sockets to some cars,
 CANBUS wiring: How does it work? - Dave_C220CDI
It does allow for some clever tricks, though.

The Vectra C has two tail light bulbs in each rear cluster. All the bulbs are 21w single filament items. With all bulbs in working order, the electronics will pass a small current through all four when the sidelights are switched on, giving the impression of conventional 5w bulbs. When the brakes are used, the electronics increase the current to the upper pair of bulbs, giving the impression of conventional twin filament 21w/5w bulbs. If either upper bulb should blow, the electronics will then divert the brake light signal to the lower bulb, giving two full brightness brake lights even with one blown bulb. Clever.

EDIT: Like this: www.vectra-c.com/forum/showthread.php?t=3832
Last edited by: Dave_TDCi on Fri 27 Jan 12 at 20:37
 CANBUS wiring: How does it work? - Zero
The Touran I had was like that, it could even reconfigure in the event of a blown rear sidelight bulb, It was so clever it could also turn off the offside front headlight at over 70 MPH, and turn on the rear brake lights when the temp dropped to 5c and everyone was in bed.

It cleverly made a kinda dead cat squeal to indicate it had a flat battery when you opened the door, and it cleverly took 100 miles to extinguish the plethora of warning lights when you had recovered it from its flat battery state, Also clever enough to overflow the fault code log with low power warnings wiping out any other fault state that may have caused the flat battery in the first place.
 CANBUS wiring: How does it work? - VxFan
>> It does allow for some clever tricks, though.
>>
>> The Vectra C .....

Also if a front side light were to blow, it will put the indicator bulb on dimly instead. However, this isn't the case with all Vectra-Cs. Some will, some won't. Guess it depends on the year it was made.
 CANBUS wiring: How does it work? - Kevin
>..the power drain could confuse the relevant controller?

On X308 and X100 Jags the system was so sensitive that you would get spurious "Bulb Failure" messages if you replaced an OEM bulb with a cheaper generic item.
 CANBUS wiring: How does it work? - R.P.
Same on BMWs
 CANBUS wiring: How does it work? - Kevin
A section of source code from the Bosch CANbus Specifications:

if(turn_signal){

switch (manufacturer){

case BMW:
return(ERROR);

default:
.
.
.
}
}
 CANBUS wiring: How does it work? - R.P.
Don't need indies !
 CANBUS wiring: How does it work? - spamcan61
>> Same on BMWs
>>

Similar scenario with the stop and tail bulbs on SWMBO's Zafira, as I recounted some while back, the two bulbs need to be well matched in terms of cold resistance. Tried to buy a twin pack of bulbs for said Zafira in the local motor factors, the guy behind the counter couldn't understand why I wouldn't buy two random bulbs from his big box, he got quite shirty about it!
 CANBUS wiring: How does it work? - spamcan61
>> >..the power drain could confuse the relevant controller?
>>
>> On X308 and X100 Jags the system was so sensitive that you would get spurious
>> "Bulb Failure" messages if you replaced an OEM bulb with a cheaper generic item.
>>
As recounted somewhere in the backroom I had to change both brake lights on SWMBO's Zafira when one blew, otherwise the check control moaned abut bulb failure...and that doesn't use CANBUS thankfully. BMW motorbikes are very bulb brand sensitive as well IIRC.
 CANBUS wiring: How does it work? - R.P.
They are my new GS only has two though (Main and dip beam) the rest are LEDs.
 CANBUS wiring: How does it work? - Britisle
I just added 4 x reversing sensors to my 2009 Vauxhall Insignia with no problem. I wired them into the final wire going into the NS reversing light cluster. They only take 3.5 watts (according to the supplier) and they work perfectly.
 CANBUS wiring: How does it work? - Runfer D'Hills
Wish you'd stop blowing that sodding horn. It's just not necessary. Engage eyes and and idiot filter and you can waft along in serene calm....

:-)
 CANBUS wiring: How does it work? - R.P.
How else does one's acknowledge the staff when one encounters them on the byways ?
Last edited by: R.P. on Fri 27 Jan 12 at 20:59
 CANBUS wiring: How does it work? - Zero
Why did we never offer an invite to Toad of Toad hall to join this site?
 CANBUS wiring: How does it work? - Runfer D'Hills
Mine salute me and I in turn nod almost imperceptibly in return.
Last edited by: Humph D'Bout on Fri 27 Jan 12 at 20:53
 CANBUS wiring: How does it work? - -
Thanks for this thread, just got round to thinking seriously about a 59 reg C250CDi MB bluewhatever it is estate, seen one we fancy too in a lovely light blue metallic.

That silly idea now scrapped, phew.
Last edited by: gordonbennet on Fri 27 Jan 12 at 20:54
 CANBUS wiring: How does it work? - Runfer D'Hills
Luddite
 CANBUS wiring: How does it work? - -
Thanks Hump, thats real praise and i'm delighted.
 CANBUS wiring: How does it work? - Zero
To be fair, systems are much better understood, designed and implemented (things like not fitting one of the controllers in a well under the floor mat under the leaking pollen filter for example), so work much better on new cars. As long as you have no intention of fiddling with them.
 CANBUS wiring: How does it work? - R.P.
The bike has CANbus - needs specially configured chargers and that - but a bit of a pain really.
 CANBUS wiring: How does it work? - Dave_C220CDI
>> just got round to thinking seriously about a 59 reg
>> That silly idea now scrapped, phew.

Is everything CANBUSsed now? I've been towing with a 61 reg Hilux Invincible for the last couple of days and it behaves in a pretty old-school way. When I use the fairly meaty stalk to flash the (H4) headlights whilst the dipped beams are on, it toggles between main and dip rather than overlays one on the other, with a clicking relay to be heard behind the dashboard as the switch makes contact. My N-reg Carina did the same thing.

The Hilux really seems built to last, even down to the computer and stereo both using 7-segment LCD displays rather than less resilient multi-pixel screens. I can easily see this one battering around an African desert in 20 years' time.
Last edited by: Dave_TDCi on Fri 27 Jan 12 at 22:12
 CANBUS wiring: How does it work? - Zero
Not all news cars embrace canbus fully, some are half old tech new tech hybrids
 CANBUS wiring: How does it work? - Dave_C220CDI
That would seem reasonable, it's got lots of mod cons (climate, cruise, buttons on the 'wheel etc) but nothing that couldn't be had on a Vauxhall Carlton twenty years ago.
 CANBUS wiring: How does it work? - Old Navy
Are the CANBUS controllers robust enough to switch heavy loads, (like headlights) or do they activate relays? My car has CANBUS and relays for the heavy stuff, as did my MK2 Focus.
Last edited by: Old Navy on Sat 28 Jan 12 at 08:47
 CANBUS wiring: How does it work? - sajid
i heard about canbus, a clever wiring set up, using the controllers, it also saves the manufacturers meters of cable not required by canbus, thus saving additional weight, if canbus wasnt fitted.

On the downside, there the reliabilty, of canbus wiring, think some french cars, vauxhall cars do have problems with the wiring looms, see the honest john car by car reviews
 CANBUS wiring: How does it work? - Zero
Can be a mixture of electronic switching and relays depending on the application and current.

The canbus controllers will not actually do any direct switching.

You can't expect the supervisor to do the manual work now can you.
Last edited by: Zero on Sat 28 Jan 12 at 12:06
 CANBUS wiring: How does it work? - Old Navy
>> The canbus controllers will not actually do any direct switching.
>>
>> You can't expect the supervisor to do the manual work now can you.
>>

No wonder DIY dabbling with car electrics is risky, canbus will want a union and a jobsworth award next. :-)
Last edited by: Old Navy on Sat 28 Jan 12 at 12:25
 CANBUS wiring: How does it work? - Bagpuss
I was working for a company in the late 90s designing control systems for industrial automation. CAN bus was starting to become established for networking of industrial equipment back then, due to its low cost and robustness. It's very often used these days in control systems for lifts.
 CANBUS wiring: How does it work? - Zero
I know a project manager at a satellite making company, they use canbus as well.
 CANBUS wiring: How does it work? - Old Navy
Does anyone know what happened to electrically operated (as opposed to hydraulic) brakes? There were rumblings about them a few years ago.
 CANBUS wiring: How does it work? - Bagpuss
I don't know of any purely electrical brake systems in production, though I saw prototypes about 10 years ago. It would be difficult to implement cost effectively as motoring regulations mean you need at least one redundant hydraulic braking circuit, so you would still need a complete hydraulic system as backup.

There are some electrohydraulic systems in use, where there is a sensor on the brake pedal which transmits the braking effort electrically to a pump on a hydraulic braking circuit. The Mercedes W211 E-Class initially had such an electrohydraulic brake system (called SBC) which was a disaster and Mercedes ended up retrofitting all pre facelift W211s with conventional brakes. Some hybrids use a more successful electrohydraulic setup, such as the Toyota Prius.
 CANBUS wiring: How does it work? - Zero
Regenerative braking is the holly grail now, convert as much braking energy into electricity as possible.
 CANBUS wiring: How does it work? - Old Navy
>> Regenerative braking is the holly grail now, convert as much braking energy into electricity as
>> possible.
>>

That sounds like desperation, a bit like wind farms. The tree huggers have a lot to answer for.

Mainly for giving the politicians a taxation excuse.
Last edited by: Old Navy on Sat 28 Jan 12 at 13:31
 CANBUS wiring: How does it work? - PeterS
>> The Mercedes W211 E-Class initially had such an electrohydraulic brake system (called SBC) which was
>> a disaster and Mercedes ended up retrofitting all pre facelift W211s with conventional brakes.


I don't think that's quite right; SBC was deleted from facelift cars, but there was no wholesale replacement of the system on cars already in service. MB extended the warranty on the SBC pump/controller, but AFAIK that's all they did. IIRC the pump was designed to stop after a given number of cycles, but I think MB replace them for free now.

I had an early S211, with SBC brakes, and had no problems with them. They had the now common hill-hold function, but also a system called SBC-STOP, which braked the car to halt when teh accelerator was released. Always fun trying to judge when to stop accelerating such that the car would brake iteself to a halt at the right moment - definitely a solution to a problem that didn't exist!!
 CANBUS wiring: How does it work? - swiss tony
>> >> The Mercedes W211 E-Class initially had such an electrohydraulic brake system (called SBC) which was a disaster and Mercedes ended up retrofitting all pre facelift W211s with conventional brakes.
>>
>> I don't think that's quite right; SBC was deleted from facelift cars, but there was
>> no wholesale replacement of the system on cars already in service. MB extended the warranty
>> on the SBC pump/controller, but AFAIK that's all they did. IIRC the pump was designed
>> to stop after a given number of cycles, but I think MB replace them for
>> free now.

That's closer to the truth.
The SBC pump has been replaced FOC in some cases, but its not a definite freebee.
It was designed to have a service life, that has been updated via software - a welcome bonus of the car being serviced by the dealer network.
 CANBUS wiring: How does it work? - sherlock47
Lucas (or was it Smiths?) had a demo developement system in 1968. Not the same protocol, but the same principles of centralised control with a BUS. I believe that it was abandonned because 'hardening' the electronics to cope with an automotive enviroment was too diificult at the time. Cheap integration and lack of volume production probably had cost implications as well.
 CANBUS wiring: How does it work? - -
I've been towing with a 61 reg Hilux Invincible for the
>> last couple of days and it behaves in a pretty old-school way.

Still a good motor and seeing as it wan't broke they didn't fix it. Very old fashioned company Toyota and none the worse for that, even though their hybrid cars are very technically advanced they didn't release them till they got it right.

Quick question Dave seeing as you've been using a brand new version of my now sold 57 plate, has the fuel consumption improved at all, i assume you have been using a 3 litre, mine was auto too which obviously didn't help consumption.

What sort of fuel consumption have you been averaging please?

I ask because if i do go Hilux again, blame this thread, i had considered getting a grey import 2.7 petrol Vigo and getting it LPG'd, but i'd be interested to see if the Diesel has improved in the last 4 years.
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