Technical Canbus low, pin 14 battery voltage problem

[Keith Spencer]

Hi all,
Cutting a long story short, I have a 2009 fiat ducato bessacarr motorhome and on trying a new obd scanner, I found that the can low pin 14 would rise to 12.4volts when the ECU goes to sleep.
I have checked the canbus hi/low signal with oscilloscope and signal looks healthy. Checked the end resistors and I am getting slightly low 48 Ohms resistance, should be 60.
I am suspecting a slightly faulty module/ecu/node that is leaking the voltage back when asleep.
The low resistance could be the addition of a non standard device or module onto the canbus system, possibly the tow bar, by the previous owner.
I would like to find the location of all the canbus modules so I can do a systematic removal test to find the faulty module.
I have already disconnected the abs and air bag, but the voltage remains?
If anyone can point me in the direction to obtain a wiring diagram and or module diagram that would be excellent. Or tell me where they all sit?
Many thanks Keith

 

[bugsymike]

Aftermarket alarm system?
With power off 60 Ohms between high and low canbus?
You sound a lot more familiar with Canbus systems than me, I am only able to test using a break out box via OBD port and haven't got a decent Oscilloscope .
I am testing my 2010 Doblo 1.6, bit of a learning curve at 70 but don't like to be beat.

 

[Keith Spencer]

Hi bugsy,
There is a brilliant hand held twin channel osciloscopio on the market, it's a zeeweii dso2512g, about £80 if you hunt around the usual sellers. It's perfect for doing canbus hi and low comparisons with the twin channel. PS I am only measuring 48 Ohms which is too low and suggests an additional resistor is in the canbus circuit, probably from a faulty module which is also supplying the 12.4 volt when asleep. Do you know the location of any modules?

 

[bugsymike]

Hi bugsy,
There is a brilliant hand held twin channel osciloscopio on the market, it's a zeeweii dso2512g, about £80 if you hunt around the usual sellers. It's perfect for doing canbus hi and low comparisons with the twin channel. PS I am only measuring 48 Ohms which is too low and suggests an additional resistor is in the canbus circuit, probably from a faulty module which is also supplying the 12.4 volt when asleep. Do you know the location of any modules?

Hi Keith, I did look at a four channel Pico scope at a Mechanics Show some time ago , but being retired now cannot justify the cost involved, although being specialised it gave a lot of extra support and readings to be expected in different applications etc for fault finding, so good value.
So I will investigate the Zeeweii you mentioned, I did buy a chinese single channel one to get an idea of how they work, but it appears a bit basic.
As I understand there is usually a 120 Ohm resistor either end , usually ECU and ABS giving the 60 Ohm reading on older stuff but circuits are more involved and more of them in the newer stuff making it harder without circuit diagrams.
I understand if any past repair to a twisted pair of Canbus wires is badly done it can effect readings and cause errors etc.
You sound to be more familiar with the electronics side of vehicles than me, I started my apprenticeship in 1969 when life was a lot simpler.

 

[Keith Spencer]

Hi Bugsy,
I just tried to reply to your message using the email reply facilities and it's saying not sent. It took ages to write so I will retype or resend when I have a bit more time, you will find it useful.
Thanks Keith

 

[Keith Spencer]

In brief
forget the pico, it's for professionals with 4 channel demands.
You are similar age to me 70's.
I had professional engineering career ending in MOD Cornwall.
2 channel oscilloscope perfect for DIY diagnostics, zeeweii is excellent.
Watch on YouTube, schrodingers box and Pine hollow auto diagnostics and mechanics mindset. They will show you everything you need to know. And pine hollow uses the zeeweii.
60 ohms is not dependant on network complexity.
"Alldata" for all wiring diagrams +info but subscription expensive.
I'm stuck for wiring diagram and canbus node layout location.
Sorry brief but due out shortly.
Any other advice please ask.
Keith

 

[bugsymike]

Thanks for getting back, I will look at the uTube video etc.
Re your vehicle, like you I am suspicious of any non original mods such as the tow bar, but would also include any aftermarket alarm systems, etc.
Plus would Bessacarr be able to supply you as an owner any relevant wiring diagrams specific to the the Motorhome as opposed to the basic Fiat chassis?
Some owners have issues related to leisure battery and split circuit charging systems, possibly back feeding etc.

 

[Communicator]

Hi all,
Cutting a long story short, I have a 2009 fiat ducato bessacarr motorhome and on trying a new obd scanner, I found that the can low pin 14 would rise to 12.4volts when the ECU goes to sleep.
I have checked the canbus hi/low signal with oscilloscope and signal looks healthy. Checked the end resistors and I am getting slightly low 48 Ohms resistance, should be 60.
I am suspecting a slightly faulty module/ecu/node that is leaking the voltage back when asleep.
The low resistance could be the addition of a non standard device or module onto the canbus system, possibly the tow bar, by the previous owner.
I would like to find the location of all the canbus modules so I can do a systematic removal test to find the faulty module.
I have already disconnected the abs and air bag, but the voltage remains?
If anyone can point me in the direction to obtain a wiring diagram and or module diagram that would be excellent. Or tell me where they all sit?
Many thanks Keith

Hi Keith,
Have you looked at the x250 Training Manual, which ia available in the Downloads section, at the top of the page.

Before I retired over 20 years ago, a twin channel Fluke Scopemeter was part of my toolkit. As my x244, has only a few nodes, I have not needed to use a scope, but have two other more complex vehicles, and there are other applications. I will investigate your suggestion.

 

[Keith Spencer]

I have ordered a dvd workshop manual, said to have all diagrams. Due to arrive Friday 16th June can't wait. Checked the solar panels, towbar electrics and key fob module in the passenger footwell. No joy so far.

 

[bugsymike]

Have you been able to rule out aftermarket alarms can causing issues?

 

[Keith Spencer]

Hi bugsy,
As far as I can tell it has fiat alarm fitted, found the radio had a cobbled in power supply, so pulled its fuse and made no difference :-{. Waiting for the dvd diagram to find its location, to pull the plug and see.
Strange thing is when it's running the canbus is on spec and the waveforms are perfect, including their operating voltages.

The initial thing that threw me a curve ball was that the canbus is a slow speed one in the ducato 2009, (not to be confused with can low).
So it's operating voltages are 1v to 5v can hi and 4v to 0v can low.
On a high speed Canbus the voltages are 2.5v to 3.5v can hi and 2.5v to 1.5v can low.
Also on the slow speed can bus you can only confirm those voltages with an oscilloscope set to show max/min readings, unlike the high speed network you don't get the mean of the voltages when using a dvm, across the hi/low to earth.
The fact I am getting 48 Ohms resistance, 60 is norm, 50 to 70 is just acceptable. Suggest a node is contributing additional resistance to the circuit, ie an internal diode failure, which is also allowing a small voltage onto the can low wire when inactive, it tends to vary each time measured 12.4v to 11.2v. Also suggesting a fault rather than by design, the battery being 13 to 14v on the solar system.
Anyway keep digging, plenty of thinking time at our ages lol.
Keith

 

[bugsymike]

Re the voltages, in the past on a 05 1.9 Doblo I was able to locate an issue with the wiring plug at the MAF sensor using a basic voltmeter, but on my 2010 one the readings don't seem to correlate which is one reason why I was looking at oscilloscope's as an alternative.
Still gives plenty of thinking time as you say. My problem is over thinking and knowing in the back of my mind the fault is probably something really small, but that once you give it to a "specialist" the meter starts running away with the £££££s and has been mentioned here before on Forum "the parts scatter gun approach when you look under the bonnet".

 

[SmiffDaMista]

Re the voltages, in the past on a 05 1.9 Doblo I was able to locate an issue with the wiring plug at the MAF sensor using a basic voltmeter, but on my 2010 one the readings don't seem to correlate which is one reason why I was looking at oscilloscope's as an alternative.
Still gives plenty of thinking time as you say. My problem is over thinking and knowing in the back of my mind the fault is probably something really small, but that once you give it to a "specialist" the meter starts running away with the £££££s and has been mentioned here before on Forum "the parts scatter gun approach when you look under the bonnet".

hi mate i have a doblo 1.9d 2002 do you know if the air intake temp sensor is combined with the mass airflow

 

[bugsymike]

hi mate i have a doblo 1.9d 2002 do you know if the air intake temp sensor is combined with the mass airflow

I think it is, mine had a five pin connector.
When I bought it, it chucked out loads of black smoke and that sensor had been disconnected, it was even worse when connected.
After trying a new sensor eventually I checked the readings at the plug and then tried for the same readings in the wires a short way along the loom, the result was the wiring plug terminals were knackered, once sorted I ran the care for four years , no issues apart from a Crank shaft Sensor, which once cooled down still let me drive home, so not bad for over 220k miles.

 

[SmiffDaMista]

I think it is, mine had a five pin connector.
When I bought it, it chucked out loads of black smoke and that sensor had been disconnected, it was even worse when connected.
After trying a new sensor eventually I checked the readings at the plug and then tried for the same readings in the wires a short way along the loom, the result was the wiring plug terminals were knackered, once sorted I ran the care for four years , no issues apart from a Crank shaft Sensor, which once cooled down still let me drive home, so not bad for over 220k miles.

mine keeps cutting out and not starting , got a fault code saying air temp intake sensor was shot, a weird thing i found which may have knackered it possibly i think was the cold air intake was right infront of the radiator essentially breathing hot air all the time, this also caused my heater matrix to burst also, on close inspection i think they may have been an engine swap at some point in its life, as the hole chopped out of the front where the cold air was supposed to come in was on the opposite side of the car. Do you think this could of caused these issues, thanks

 

[SmiffDaMista]

and yes this is a 5 pin connector , getting the heater matrix out was a big bloody job lol, its still in bits waitng for new one ,wow what a job

 

[Keith Spencer]

Re the voltages, in the past on a 05 1.9 Doblo I was able to locate an issue with the wiring plug at the MAF sensor using a basic voltmeter, but on my 2010 one the readings don't seem to correlate which is one reason why I was looking at oscilloscope's as an alternative.
Still gives plenty of thinking time as you say. My problem is over thinking and knowing in the back of my mind the fault is probably something really small, but that once you give it to a "specialist" the meter starts running away with the £££££s and has been mentioned here before on Forum "the parts scatter gun approach when you look under the bonnet".

Hi bugsy,
Get a good scan tool, I use the xtool d7. Gives you 4 graph facility with merge option, also bi directional control, use to pinpoint the issue and then zeeweii oscilloscope to confirm.
Good hunting

 

[bugsymike]

mine keeps cutting out and not starting , got a fault code saying air temp intake sensor was shot, a weird thing i found which may have knackered it possibly i think was the cold air intake was right infront of the radiator essentially breathing hot air all the time, this also caused my heater matrix to burst also, on close inspection i think they may have been an engine swap at some point in its life, as the hole chopped out of the front where the cold air was supposed to come in was on the opposite side of the car. Do you think this could of caused these issues, thanks

I think that sensor is unlikely to be the cause of cutting out, or the air intake position.
Do you lose water/ overheating etc.
I had a VW Golf years ago that burst a radiator due to it having stood for so long the rad cap had stuck so not relieving pressure and blew the crimped joints on the plastic/aluminium radiator.
You may want to start a new thread for this and others can advise too.

 

[bugsymike]

Hi bugsy,
Get a good scan tool, I use the xtool d7. Gives you 4 graph facility with merge option, also bi directional control, use to pinpoint the issue and then zeeweii oscilloscope to confirm.
Good hunting

Hi Keith, I use a couple of basic Launch tools and if want more a friend has a garage where I can use his Snap On Zeus with all the latest updates. I used that on one of my daughters car a Punto Evo to install a new BCM and run the "proxi alignment " program.
The problem with most generic tools I find is they are great for some and useless for others.
If I gain enough knowledge to use an oscilloscope for diagnosis properly (before I die ) another friend has a Pico version, but he is not local to me here.

 

[SmiffDaMista]

I think that sensor is unlikely to be the cause of cutting out, or the air intake position.
Do you lose water/ overheating etc.
I had a VW Golf years ago that burst a radiator due to it having stood for so long the rad cap had stuck so not relieving pressure and blew the crimped joints on the plastic/aluminium radiator.
You may want to start a new thread for this and others can advise too.

only losing water from the heater matrix, the metal work underneath the dash was all rusted so im thinking it was leaking some time, its been a brill van upto this cutting out issue, and lol im not sure how to start a thread,quite new here