CAN BUS question

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CAN BUS question

Postby s4c » Mon May 08, 2017 4:08 am

Hi

I am working on a 2007 Fiat Ducato with a fuel gauge not working. We have checked the tank sensor circuit to BCM and all is good. The BCM then sends the fuel message on the network via CAN to the cluster.

I can operate the fuel gauge via the scan tool showing the CAN network is potentially good.

I have checked the CAN network for shorts to Batt+ and to grounds.

My question is, is it possible to see a 'missing packet' on a CAN network?

I have attached a PSD of the CAN network.

Any thoughts would be helpful.

Regards

Simon
Attachments
Fiat_Ducato_2007_CANH and L 004.psdata
Fiat Ducato 2007 X250 CAN
(2.21 MiB) Downloaded 48 times
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Re: CAN BUS question

Postby liviu2004 » Mon May 08, 2017 7:47 am

To be able to see if message comes through, you need to reverse engineer the canbus data.
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Re: CAN BUS question

Postby Martinjensen » Mon May 08, 2017 12:28 pm

Did you try to remove the battery terminals and holding them toghether. I had one where the system returned to normal operation after the batteri was disconnected for 10 minutes.

Regards Martin
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Re: CAN BUS question

Postby Mark Dalton » Tue May 09, 2017 12:25 pm

For a couple of reasons I think you're chasing the wrong thing here.
-Chasing things like packet data is going down a very deep rabbit hole.
> What is the PID?
> What's the formula to convert the data.
> Is it CAN or a proprietary mutation in a similar fashion to GMLAN.
- Why would the module that's transmitting the fuel level data stop transmitting only that data?
- Or why would the Instrument Cluster start ignoring only that data?
- If you think it's getting lost in transmission, why only that data?

A short to B+ or B- would destroy all data on the bus, not just certain PID's
Driving the gauge with the scan tool only tells you that the driver for that stepper motor is working ok, it doesn't tell you anything else.

Can you see the fuel level as a data parameter in the BCM and can you then do the same for the cluster, do they both state the same figure?
How often does the BCM transmit the fuel level data? You BCM fuel level data may be "live" but the Cluster data is very unlikely to be, otherwise you're fuel gauge would never sit still as the fuel sloshed around in the tank.
If there was an intermittent high resistance in the fuel sender and the BCM transmitted 0% to the cluster and then the conditions were not met to trigger the BCM to transmit the data again you could have one module with correct data and another with incorrect data.

Does the Cluster have a trip computer i.e. fuel range, fuel consumption etc. and does it work?
Maybe fuel data comes from the Engine ECU, not directly from the BCM
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Re: CAN BUS question

Postby s4c » Wed May 10, 2017 4:02 am

HI Mark

Thanks for taking the time to answer this one.

'Can you see the fuel level as a data parameter in the BCM and can you then do the same for the cluster,'

BCM does not show fuel tank level, however, cluster shows 0%

'Does the Cluster have a trip computer i.e. fuel range, fuel consumption etc'

No it doesn't

'Maybe fuel data comes from the Engine ECU, not directly from the BCM'

According to the wiring diagrams, fuel level sensor sends a varying voltage to the BCM, we have removed and tested the level sensor and even substituted it is variable resistors. It is then sent via CAN to the cluster

Seeing how the scan tool can drive the gauge, via CAN, im at a loss where to go from here.

Any comments would be great.

Simon
Attachments
Ducato 03.png
Ducato 02.png
N040 Fuel Sender
Ducato 01.png
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Re: CAN BUS question

Postby Technician » Wed May 10, 2017 10:31 am

Is there any stored fault codes for this?

Found this link, not a electrical investigation with scopes as such but might be of some help for advice.

https://www.youtube.com/watch?v=_hZW2FZeNU8

P.S. Think this thread should be in diagnostic discussion!
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Re: CAN BUS question

Postby s4c » Thu May 11, 2017 12:24 am

P.S. Think this thread should be in diagnostic discussion!


You could be right, but I started this post as a software question!

I will check log and report back

Simon
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Re: CAN BUS question

Postby Mark Dalton » Mon May 15, 2017 4:10 am

It's a pain the ass we can't see the fuel level as the BCM sees it.
The psdata file you uploaded isn't much use unless you knew the PID for the fuel level before hand.
Reverse engineering is tricky for numerous reason as I said in my last post, but on top of that Fuel Level is gonna be one of those messages that is not transmitted regularly, other than maybe at Ignition On.
If you disconnect the fuel sender do you get a DTC, Open Circuit?
If you bridge the Sender Circuit do you get a short circuit DTC?
Is there Fuel Level data in the Engine Data? The engine ECU might use fuel level data for EVAP or to disable misfire detection below a certain level.
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