# Auto electrics and Can Bus wiring



## HARRYH (May 18, 2005)

Hi 
Can anyone guide me to a web site that explains in plain english with wiring diagrams what Can Bus is?
All new Mh & cars now seem to have this wiring and it would be nice to have some knowledge of what its about.
Can a simple wiring of the light circuit be on Can bus, or is it only applicable complex systems?
Putting "CAN BUs " in to the web brings up info. that is to me to technical or to obscure.
Harry


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## Stanner (Aug 17, 2006)

As I understand it instead of lots of wires doing just one thing (e.g. power a light) as you get in "old fashioned" wiring looms CanBus has one wire telling lots of things all powered by a sort of ring main what to do.
Each item has a slave controller that is told what to do by a central controller via a "network".

http://en.wikipedia.org/wiki/Controller_area_network

And sorry it seems that's about as simple as it gets.

As the saying goes there are 10 types of people - those who understand binary and those who don't.

I'm not one of the 10.

Perhaps someone who is can explain it better to me as well.


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## pippin (Nov 15, 2007)

I am hexadecimal and I still cannot get my head around it!

That Wiki page is typical of theoretical explanations - what we need is the *applied*.

I will hunt around a bit more on the www.


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## b16duv (Feb 14, 2006)

Ok, I'll have a go!

The CANbus system uses two circuits - 1 for power and 1 for control.

The Power circuit is like a house ring main - a loop of wire running round the vehicle carrying 12v dc and connected to each 'appliance' by a 'relay'.

The control circuit sends messages round the vehicle from the switches.

At each 'appliance' say a tail light, there is a 'relay' that is controlled by the control circuit and this switches on the power from the ring main at this point, providing 12v dc to the appliance (ring main).

That's how I understand it, in non-techie speak. Apologies to the techies if I have used technical terms (Relay, appliance etc) incorrectly.

HTH

David


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## Dukeham (Feb 3, 2009)

The best way I can describe it is a load of more unneccessary crap to make the modern vehicle even more complicated than it already is !
Bring back the Moggy 1000.
GC


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## camallison (Jul 15, 2009)

Dukeham said:


> The best way I can describe it is a load of more unneccessary crap to make the modern vehicle even more complicated than it already is !
> Bring back the Moggy 1000.
> GC


.... but, it DOES take about 50kg of copper out of the vehicle build. Weight and cost are of great concern to us all?

Colin


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## Rio (Oct 17, 2007)

*can auto electrics*

Hi Harryh, here is my attempt to expain can this is a basic overview
as stanner explained , there are a number of control units ,
they communicate similar to your broadband internet with few wires and encoded signals,
they have a power supply and switch things when a command is given and send back a message to say the function was successfull,
as an example ; you press the remote key central locking which is checked by the body control unit , which is verified and an unlock command sent to the door control units , the body contol unit also switches the interior light on ,,the alarm off, the headlights on flashes the indicators and lights the dash display,and switch the fuel pump on to prime the fuel system ready for starting the engine,
the main control units are, engine, brake , body, door, and gateway which is a communications server which provides a very accurate diagnostic interface , there are many more
can wiring in the looms are twisted pairs, all the control unit loads are calculated , so that the battery manager can power save by shutting down non essentials to stay mobile or adjust the alternator output,
so if the extras are wired to a non acessory live , the control units dont shut down because they are confused, this also applies to direct wiring to the engine battery, which bypasses the battery manager which measures no load current, its a no no 
only use acessory feeds that are supplied for extras [ as per new ducato] or wire to the leisure battery, regards rio


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## erneboy (Feb 8, 2007)

It also takes the reliability out of lots of vehicles and make it hard to diagnose and fix faults, Alan.


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## Dukeham (Feb 3, 2009)

Hi Colin.
Alan has hit the nail ! Give me ease of repair & reliability over weight any day.
GC.


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## pete4x4 (Dec 20, 2006)

Actually it makes it much easier to diagnose faults, all you have to do is ask it what's wrong and it will tell you the offending module.
Ebay has OBD readers from around £30 upwards. I paid £70 for mine and it's a really useful tool for all 4 of my vehicles.

Pete


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## erneboy (Feb 8, 2007)

Live and learn Pete, thank you very much for that gem! Could you give us a little more detail please ie: 

Where do you plug it in, is it universal or does it come with a range of fittings. How does it display the info etc. 

Finally and most importantly can an old fashioned idiot spannerman like me operate and understand it, Alan.


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## sideways (Jun 2, 2008)

I understand from my local auto electrician that when they fit extras like those big rows of lights you see on lorry cab roofs, they make up a new loom and connect direct to battery so as not to interfere with the canbus system.


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## CliveMott (Mar 10, 2008)

4 wires can do it all -:
Positive supply
Negative supply
CAN HI data line
CAN LO data line.

Any CAN module can send or recieve data / instructions to any other.

But it has one major downfall, it requires SOFTWARE and you cannot sort it with a test lamp and a couple of wires. Its a CAN box and a Laptop jobbie.

Its all about reducing the cost and weight of wiring.

Its here to stay for most vans and most modern cars.

C.


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## Codfinger (Jan 11, 2008)

*can bus*



pete4x4 said:


> Actually it makes it much easier to diagnose faults, all you have to do is ask it what's wrong and it will tell you the offending module.
> Ebay has OBD readers from around £30 upwards. I paid £70 for mine and it's a really useful tool for all 4 of my vehicles.
> 
> Pete


Sure but £350 to repair an indicator fault ????????? sorry sir its not just a case of faulty bulb or flasher unit you need a new control unit oh and by the way that will have to be programed into the vehicle ecu!!!!

Progress :roll:


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## erneboy (Feb 8, 2007)

Clive, I take it then that a 30 quid home diagnostic thingy will not do the job, Alan.


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## CliveMott (Mar 10, 2008)

Dunno about the £30 jobbie. I have never (yet) had need for one with any cars or motorhome. Our previous MH was non CAN. Our current one is CAN and works Ok (CBE). Our larger fork lift trucks are all CAN and you need a CANBOX, LAPTOP and the requesite software to do anything. Different access levels of software for different customers. Like the designers can get at everything, the factory can get at lots, service engineers have limited access and customers in the most part can only look. 

But even the most sophisticated CAN structured MH can be made to work if the CAN goes belly up. With a few links fitted around the fuse box the CAN system can be totally by-passed and lights heating TV, water, loo etc be made to work.

C.


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## wobby (May 1, 2005)

pete4x4 said:


> Actually it makes it much easier to diagnose faults, all you have to do is ask it what's wrong and it will tell you the offending module.
> Ebay has OBD readers from around £30 upwards. I paid £70 for mine and it's a really useful tool for all 4 of my vehicles.
> 
> Pete


Thats if you know what your doing, I don't.

Wobby


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## wobby (May 1, 2005)

CliveMott said:


> Dunno about the £30 jobbie. I have never (yet) had need for one with any cars or motorhome. Our previous MH was non CAN. Our current one is CAN and works Ok (CBE). Our larger fork lift trucks are all CAN and you need a CANBOX, LAPTOP and the requesite software to do anything. Different access levels of software for different customers. Like the designers can get at everything, the factory can get at lots, service engineers have limited access and customers in the most part can only look.
> 
> But even the most sophisticated CAN structured MH can be made to work if the CAN goes belly up. With a few links fitted around the fuse box the CAN system can be totally by-passed and lights heating TV, water, loo etc be made to work.
> 
> C.


Again, if you know what your doing


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## pete4x4 (Dec 20, 2006)

£30 will provide you with the ability to read the fault codes and reset the Check engine light. You will then need to look up what that numeric code means.

£70 will tell you in english what the fault code means so you don't have to look it up It will also tell you loads of other stuff like turbo boost pressure, oil temperature O2 sensore etc etc.

It is a standard so there is a standard connector, the interface between manufactures can vary but most of the modern readers cope with that and they are upgradable via the internet.

Most useful feature is to be able to reset the Check Engine Light and take you out of limp home mode. Allows youn to check it is a genuine fault and avoid the £350 repair bill for a faulty indicator. By the way change your garage, your being ripped off!

You can also get a reader interface for your laptop, but to be honest readers are so cheap now I wouldn't bother unless you want to get into re-mapping.

Just search ebay for OBD Reader

Edit, I haven't yet looked for the connector on my 09 X250 so I don't know where it is but it should be drivers side in the footwell. Although there are rumours around that FIAT still use their own but that's against European law so I doubt it  I'll have a look tomorrow


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## Codfinger (Jan 11, 2008)

*can bus*

Is this any good? http://www.gendan.co.uk/product_GDEOBD.html


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## gnscloz (Oct 4, 2008)

dont necessarily make things easy to diagnose, previous mh, peugeot x250 base started acting weird lights on off without touching switch, running like bag spanners went into dealers cut long story short new ecu fuse box body control unit all new stalks to no avail, turned out internal fuel cut out switch faulty, 4 weeks £2850 luckily covered under warranty, spoke personally to a "master tec" who said was not uncommon to be led up garden path by the can bus giving out false readings to the obd reader


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## erneboy (Feb 8, 2007)

Thanks Pete, would you mind explaining what the 70 quid option is please, what is it called, Alan.


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## pete4x4 (Dec 20, 2006)

OBD Reader

Now £59.99 and its got a helpline. I have found it useful but haven't used on my FIAT motorhome.


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## CliveMott (Mar 10, 2008)

All motorhomes should come with a manual which includes a connection diagram. In the event of an emergency if the CAN goes belly up then things can be got working by pulling the individual fuses for the required MH functions and after identifying which side of the fuses is the function side linking them to a positive supply VIA A FUSE.

But if you don,t know what you are doing then don,t dabble. Find a man who CAN .

(CAN geddit?)

(Doesn,t everybody carry a full toolkit, solering iron, spare fuses, multimeter etc?)


Pardon? Payload. Yes loads and loads!


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## Autoquest (May 16, 2007)

All easily bypassed as has already been mentioned. I wired a fused electrical block to the back of the van from the leisure battery plus a further block relay switched from an ignition feed from the radio - same again to the front of the van. Now I have a ready source of electrics either directly fed for say the fridge fans or switched for the reversing camera - up front I can have a permanent live feed to the radio and tap in for stebel horns etc

simples


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## CliveMott (Mar 10, 2008)

Simples is spelt with a Z
simplez!


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## Autoquest (May 16, 2007)

Thanks Clive 

http://www.comparethemeerkat.com/home


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## CliveMott (Mar 10, 2008)

Well it is when I write it!


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## eribiste (May 1, 2005)

gnscloz said:


> 4 weeks £2850 luckily covered under warranty, spoke personally to a "master tec" who said was not uncommon to be led up garden path by the can bus giving out false readings to the obd reader


We can all get led up the garden path by the artifice of man. Some years ago our new Rapido 740F developed a disconcerting habit of having the engine die, usually at awkward and embarrassing moments. The middle of Dieppe in rush hour was a particular horror! I did all the fuel supply checks I could think of to no avail. So did the dealer's best technician. Hours later, it turned out to be an intermittent fault in the impact sensor, that doo-hickey that shuts off the fuel supply in the event of a shunt. Thankfully, all the work was done under warranty, but it must have been a small fortune.


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## Patrick_Phillips (Aug 17, 2006)

For those who want to know a bit more about how CANBUS wiring works and have some basic electronics know-how, here is a brilliant e-learning site. Not only is it good for getting the stuff learnt but it is an exemplary site for the way it is presented, IMHO.
http://www.vector-elearning.com/vl_einfuehrungcan_portal_en,,378422.html
and it is free!

Patrick


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## pete4x4 (Dec 20, 2006)

*Re: can bus*



Codfinger said:


> Is this any good? http://www.gendan.co.uk/product_GDEOBD.html


I've no idea, I've only tried two, one for the laptop and then because my Jeep developed annoying habit of saying my Throttle position sensor was open circuit and put me into limp home mode I bought the portable one that I have already mentioned to take with me and get me out of limp home mode.

They all do more or less the same thing, you pays your money you takes your choice I'm afraid. It looks like a good entry level device. It allows you to turn off the Check engine light and seems to suggest it will tell you what the fault is in English.


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## Rainbow-Chasers (Sep 2, 2008)

In laymans terms - if you add any electronics, it has to be programmed in so the brain knows it is there or it will shut the lot down.

You can bypass the whole system as already explained.


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## Hymie (May 9, 2005)

*Canbus*

I remember reading somewhere that on X250 based motorhomes, only the cab area runs on the original "Canbus" system - the rest of the vehicle runs traditionally via an adaptor of some sort??

Does that sound correct??

I cant remember where i read it but it was when the first X250 based units were produced.

Im interested to know if this is so??.

Happy Travels

Dave


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## CliveMott (Mar 10, 2008)

Sargent make a CAN adapter for UK MHs on this chassis.

C.


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## pete4x4 (Dec 20, 2006)

My step is connected to the Canbus as is the towbar electrics, that allows it to link into the bulb failure bit so it doesn't need a tell tale on the dash when you indicate.

Fiat X250 2008/9


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## pete4x4 (Dec 20, 2006)

Rainbow-Chasers said:


> In laymans terms - if you add any electronics, it has to be programmed in so the brain knows it is there or it will shut the lot down.
> 
> You can bypass the whole system as already explained.


It only needs to be programmed in if you want the canbus to know its there. There are plenty of after-market accessories that take feeds off the Canbus, In car entertainment is probably the biggest, looking for canbus info on whether lights are on, ignition, speed to auto adjust volume, handbrake so you can't watch dvd while your moving, simplest one for us is the electric step which looks out for the ignition being enabled and then retract.


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## Rainbow-Chasers (Sep 2, 2008)

Step probably would cause no problems - I have seen many cooked ECU's through having after market towbars fitted without the system being programmed - doesn't always cook straight away either! I have seen cars that have had the towbar on for 7 months, and all of a sudden the car shuts down. 

We had to be careful on the recovery vans with all the extras on them. 

It is all just a rip of by the dealers to stop you getting cheaper, or non approved add-ons!


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## HARRYH (May 18, 2005)

*can bus*

Thank you all for the infomation.
Interesting but Im still confused
Is this it?
Ring main 12volt I undestand as simple electrics 
Relay control at each function with each relay controlled by the switch or the operation of an action. Thats not a problem.
A wired in computer chip measures elctric loads and that all relays that are in that particular circuit programme are working as they should either open or closed. If there is a fault the warning shows and programmed action is take and recorded in the memory.
What I would like to see is a simple circuit diagram that compares a "can bus" to a "old circuit"
It would be helpfull to be able to talk to and undestand the Guy thats taking my money for repairs.
When that warning light comes on it seem that you,r giving a blank check .Because even if you pay for the diagnostic that shows a faulty ECU "relay with a chipI think" when that Ecu is replaced a futher diagnostic check could show another fault and so on.
The garage are unable to give a reasonable fixed Quotation for repair costs.
I was interested in a sugestion that a "can bus" circuit could be by-passed in an emergency. I suppose that only would apply to some circuits. and you would require a circuit diagram and details of the wire locations. 
Any one got the wiring diagrame for a Ducato X250 2007 or know where to buy one.
The x250 is a nice van to drive, pity about xxxxxxxxxxxxxxxx.
Harry


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## Patrick_Phillips (Aug 17, 2006)

Let me see if I can pitch this explanation right :? 

In the first diagran we have a conventional setup where turning on a switch completes the positive wire all the way to the bulb and the return is via the chassis earth.

In the second diagram the CAN system is added.
Here the bulb is plugged into a CAN transceiver. This tranceiver has small "message" wires (called CANHigh & CANLow) to the ECU or controlling computer.
The CAN transceiver has a relay that can be switched so that the bulb is connected to the heavy-weight Positive bus (or ring) in much the same way as throwing the switch in the conventional wiring.

The switch, however, is connected to the computer or ECU. Operating the switch causes the computer to send out a message to the CAN that operates the relevant bulb etc.

The CAN unit at the bulb not only switches the bulb on but sends a message back to the ECU to say that it has done so and that the bulb is drawing current (ie. working).

The message bit is called a packet. It is a short burst of information that has an "address" at the front of it. Only the CAN which is listening for that specific address will react to it. The rest of the CANs in the system will see the message but just ignore it.
This means that just two wires going round the whole system carry all messages back and forth. The only other wire that is needed is the heavy bus wire carrying the positive to the battery.

CAN units can read and send a variety of messages, ie:
"I have switched it on"
"The device is drawing current"
"The device is drawing n amps of current"
"The temerature of the device is n degrees"
etc. etc.

Sometimes these messages show more useful information if you look at a whole series of them over time.
A CAN might be reporting the temperature of the engine. This means more once the engine has warmed up. If the temperature continues to rise, maybe something is wrong.
For this reason, the ECU stores many thousands of messages and will make decisions about the state of the vehicle from its history log.
If the engine is getting too hot because the engine is having to work very hard, that may be OK for a while.
If, on the other hand the engine is getting too hot when just light duties are being done, then the situation needs watching - not by you, the dumb driver, but by the ECU.
When it feels that a bad situation has built up, the ECU may decide to put everything into "limp home" mode to protect the engine.

Unfortunately, the history log may lead it astray and you could find yourself limping home for no good reason.
If the history log is wiped clean then the ECU starts all over again and the ECU is said to be "reset"

The devices that the garage use, and you can too, allow you to read the history logs for each device and, most of them will allow you to reset the devices.

Of course, if you disconnect the bulb (ro whatever device) from the CAN and give it a switched line to the positive terminal on your fuse box, you will have bypassed the ECU/CAN system altogether and it will work like a conventional (or older) vehicle.

Gosh, if I have pitched that explanation wrong, that is a lot of wasted electrons. But heres hoping!
Patrick


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## granneb (May 27, 2008)

Hi

This thread is quite a revelation, and I think I'm begining to understand some of it, :roll: 
However just one question, to Clive, I take it that connecting the leisure battery to the vehicle battery with one wire and a fuse, for charging purposes, doesn't effect the can system?

Regards

Graham


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## HARRYH (May 18, 2005)

Thanks Patric- Philips
Thats an explanation I understand. A sketch is worth a load of words.
and the words made sense to me as well. Thanks again.
It seems we are all stuck with Can BUS in new vans like it or not.
At least in the MH we have the other simple system in the back " as yet."
Ps just had a engine management light come on and diagnosed as a EGR valve fault not covered by warranty. £80 to diagnose the fault, £165 quote to change it. and the garage cant say for sure if thats all it is.
An open check book for putting the dash light out??????.
Oct 2007 and only 6000miles covered. Fiat have offered to supply the part free of charge, but it all hassle and expense I can well do with out.
Thank goodness my other cars are Honda


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## emmbeedee (Oct 31, 2008)

HARRYH said:


> Thank goodness my other cars are Honda


Don't think this doesn't happen to Japanese cars!
Our neighbours two doors down have a Lexus diesel. 07 reg., they have had it from new, now 24k on the clock. Very happy with it, always telling us how good it is, better than their previous Jag., etc., etc.
So imagine how surprised we were when it went off up the close on the back of an RAC truck. This was two months ago, but it has now happened five times so far & the dealer still doesn't know what the problem is. Goes in to limp home mode quite regularly.
First diagnosis was EGR valve, then pipe blocked, then another pipe blocked, but since had engine stripped down & piston rings changed & still not solved. 35 hours labour to date. Fortunately they are doing it under warranty, but you can imagine the bill if out of warranty.
The dealer did say it was neighbour's wife, not driving it hard enough, as she is the main driver. So last time it was "fixed" the service manager decided to take it home himself every night for a week. Guess what, happened to him several times. Still at the dealers & my neighbour is not a happy bunny! :evil:


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## HARRYH (May 18, 2005)

Frightening that all these electric checks seem to result in none faults or a wrong diagnosis. Is it that in the end the car electrics will be all disposable modules because the garages lack the experts that are needed to understand and repair the complex systems
It seem that "warning light on" and if the garage are not sure whats wrong "change an EGR valve " as a safe stab in the dark that a costumer wont question the charges.

Whats an Egr valve and how and why does it fail or show fault?
Are some "Can bus" systems more tolerant than others?.
One of the Mh. pleasures at least to me was the adding of gadgets to my old motor home a pleasure Ill have to forgo with this new one. At least if its to the cab side of the electrics.


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## tlittle (Sep 11, 2008)

Hi,
If it helps I use a Autel MS509 on a 2008 Fiat ducato.

see http://www.auteltech.com/ms509.htm

Is read all codes and reports the code in english+ a few other features

£60 on EBAY

I thought I add a reply tp this post just in case someone wants a code reader that works on the FIAT
I hope this helps.

Thanks


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## emmbeedee (Oct 31, 2008)

HARRYH said:


> Whats an Egr valve and how and why does it fail or show fault?


Well, I can answer this bit. An "EGR valve" is an exhaust gas recirculation valve & is used to recirculate exhaust gas from the exhaust manifold into the inlet side of the engine. As such it has to deal with extremely hot gas which can cause it to clog & stick. 
Why is it there? To reduce emissions of harmful exhaust gases. Feeding controlled amounts of exhaust gas into the engine in this way does significantly reduce certain pollutants.
No doubt about it, though, all of these gizmo's, fitted with the best of intentions, do make diagnosing & fixing problems a nightmare at times.
I had this a few years ago with my Alhambra (1.9 TDi). Kept going into limp home mode, with increasing frequency. Back to the dealer multiple times, keeping it for longer each time (four weeks last time) & couldn't find the fault. (ECU said "charge pressure difference"). Eventually, after FIFTEEN months, they found leaking seals in the turbo. To rub salt into the wound, they then tried to charge me for the turbo (£750), but agreed not to charge labour "as a gesture of goodwill". Needless to say, as it was first reported under guarantee they got a very dusty answer to that one.
As with all of these systems, they are all wonderful in theory, with designers sitting in offices agreeing how good they are. Unfortunately, reality is often somewhat different to their dreams.


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## SpeedyDux (Jul 13, 2007)

Yikes, after reading this thread I think I will stick with the old-fashioned wiring loom type of vehicle electrics. I never thought the electrics were a Fiat strong point anyway, although their mechanicals seem quite rugged (apart from certain gearboxes).

Canbus doesn't look to me to be a very resilient way of doing things. Nor is it well suited to the skill level you find nowadays in Main Stealerships if you need to get a problem diagnosed correctly and fixed without incurring inflated bills.


SD


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