CanBus on Transit Custom

If you are not a PicoScope user and want advice with a diagnostic problem then post here. Forum members may be able to help.
User avatar
Fat Freddy
TwoWaves
TwoWaves
Posts: 335
Joined: Fri May 04, 2012 4:52 am

Re: CanBus on Transit Custom

Post by Fat Freddy »

Hi Richard.

I must apologize. 'Good' is probably not the right wording. A lot better is a more suiting term. I hadn't applied the Maths for the download.

I agree. I would have considered it unusable also and was surprised it was still a valid bus with the right software/hardware.

And no I don't have a after capture after repair but here is a capture with the PCM disconnected. Still not perfect but IIRC other scan tools could then communicate.

User avatar
FioranoCars
TwoWaves
TwoWaves
Posts: 386
Joined: Thu Dec 13, 2012 11:26 am
Location: London, UK

Re: CanBus on Transit Custom

Post by FioranoCars »

Thanks FF
That's great, just wanted to see if it was a 2.5v base with something in the Engine ECU chipset pulling up the voltage to the weird levels, or if this was some other "new" operational voltage level ... clearly it should be 2.5v, which is re-assuring!

Hope the weather is good out there, we might be getting snow this weekend over here :-(

Cheers
Richard

User avatar
STC
Banned
Posts: 790
Joined: Sun Sep 13, 2015 2:10 am

Re: CanBus on Transit Custom

Post by STC »

There is no stipulation for Can Voltage - It can be anything.

Mercedes Benz Body CAN is recessive (asleep) at circa 8v.

When examining the system for parasitic drains, measuring 8v on that network is a PASS. Move on ...

The variables are numerous - endless ...

It is a case of Specialising in a brand or 2, either that or be a busy fool - like me - always playing catch up.

lukascz
Newbie
Posts: 1
Joined: Tue Jan 15, 2019 10:46 am

Re: CanBus on Transit Custom

Post by lukascz »

Hello, I have the same problem with Ford Custom. Can-bus data are sporadically wrong. What was your cause of the problem?
Best regards.

Mr. Wizard
Newbie
Posts: 2
Joined: Tue Mar 08, 2016 8:21 pm

Re: CanBus on Transit Custom

Post by Mr. Wizard »

It seems there are a lot of mysteries, myths, misunderstandings, smoke and mirrors, and just plain old misinformation out there regarding CAN Bus. I will share what little I know and muddy the waters even more. This is a high level overview and not a step by step guide. It assumes you are a master level tech with advance troubleshooting skills.
Note: The trace showing channel A minus channel B being below 2 volts is not an issue.
IMHO: you have the wrong Node on the Alternator.
Overview:
CAN Bus has two basic layers.
• Physical layer
• Data layer
The physical layer consist of
• Wiring (twisted pair / Balance Line)
• Termination Resisters
• Nodes
• Power and Grounds at each Node.
Data Layer
• Massages and signal information.
• part A is for the standard format with an 11-bit identifier
• part B is for the extended format with a 29-bit identifier
• CAN FD (Flexible Data Rate)
• And others.
For the most part Technician should ignore data layer part of the Bus. It is safe to have the mindset the vehicle worked right up to the point it came into the shop, there are thousands of others out in the world working fine, and the hardest pill to swallow; yes the engineers know what they were doing when the designed the system.








The Basics of the Physical Layer:
• Nodes communicate over a pair of twisted wires.
o The twisted pair of wires should only connect to nodes, NOT Ground or Battery Positive.
o By twisting the wires; induced voltages will be the same in both wires and canceled out in the transceivers.
o The twisted pair has a starting and ending point with branches in-between.
o The starting point will have a 120 ohm termination resister, along with the ending point.

o One wire is called CAN High
o One wire is called CAN Low

• Nodes use transceivers to connect and communicate with other Nodes over the Bus.

o The Bus network may consist of just two nodes or have hundreds if needed.

• CAN High and Low
o CAN High (Blue)
 Is at rest at ±2.5 Volts (Recessive)
 Is at active at ±3.5 Volts (Dominate)
o CAN Low (Red)
 Is at rest at ±2.5 Volts (Recessive)
 Is at active at ±1.5 Volts (Dominate)

• The Bus has only two states, Recessive and Dominate
o Recessive (The Bus is at rest)
o Dominate (The Bus is active)


Troubleshooting CAN Bus:
As technicians we should focus on the Physical Layer, as this is the part of the system with the highest failure rates and the one we don’t need PHD and proprietary information to decode and understand.
I always start my CAN Bus troubleshooting the same way and follow the same basic test procedure and fix 99 plus % of all issues in a fairly short time frame. First we need to determine is this a CAN Bus issue or something else. Ask yourself, what leads me to believe this is a CAN issue, do I have a Communications DTC or is something not working and I’m assuming it’s CAN related?
Print out the Network Diagram and spend I few minutes studying it. (If the window will not work and the window is not controlled by a CAN Node, IT’S NOT A CAN BUS ISSUE!). Sorry for that, you would not believe how many times I get a call about CAN Bus problems and the non- working device is not CAN controlled or everything else on that Node works fine except the one thing they are asking about. i.e. if everything in a door is controlled by a Node/ door module and the window is the only thing not working, IT’S NOT THE CAN BUS!

Scan Tool:
Connect to the Bus and do a roll call (Scan all Nodes for DTC). Let the scanner scan the Bus and report back all the Nodes it communicated with, on some vehicles this may only be a few and on others more then I care to think about. On The Network Diagram you printed out Mark All The Nodes The Scan Tool Communicated with. This may take a few minutes depending on the number of Nodes but can pay great dividends if several Nodes are not working and are all located on the same branch of the network.

• Was the scan able to communicate with all known Nodes?
o Yes (Most likely not a CAN issue, possibly a Node issue.)
o No
 How many Nodes failed to communicate
• All (Confirm tool works on a different Vehicle)
o See troubleshooting with DMM
o Opens, Power and Grounds
• One (Is this Node associated with the issue?)
• Several (How are the Nodes connected or grouped on the Network?)
o Are they all connected to the Network beyond a point
o Do any Nodes Beyond them communicate
o Do they share Power or Grounds

DMM:
The Digital Multi Meter is not the best tool for troubleshoot the CAN Bus but most technicians have one and it is a good starting point.
With Key on and Network active set meter to DC voltage, Connect to a known good Ground with negative lead, with positive lead check the following.
CAN High line. Meter should read greater than 2.5 volts and less than 5 volts. (Between 2.5 and 3 volts is typical)
• Reading’s lower than 2.5 volts indicate CAN High is shorted to CAN Low or Ground. This could be the wiring or a Node.
• Reading’s Higher than 3.5 volts indicate CAN High is shorted to Power other than Node transceivers, Battery Positive. This could be the wiring or a Node issue.

CAN Low line. Meter should read less than 2.5 volts and greater than 1 volt. (Between 2.5 and 2 volts is typical)
• Reading’s greater than 2.5 volts indicate CAN low is shorted to CAN High or Battery Positive. This could be the wiring or a Node issue.
• Reading’s Lower than 1 volts indicate CAN Low is shorted to Ground other than Node transceivers, Battery Negative. This could be the wiring or a Node issue.
CAN Bus Resistance:
Disconnect the vehicle battery, using you DMM set to resistance measure between the CAN High and CAN Low terminals of the Network. You should read about 60 ohms of resistance; this is an important part of the Bus Net Work and should not be overlooked.
• A reading of 60Ω indicates both termination resistors are connected to the Bus
• A reading of 120Ω indicates one of the termination resistors is not connected to the Bus and will need resolved before moving on.
• In some rare cases you may see a reading below 60Ω, about 40Ω. This is an indication Both termination resistors are connected to the Bus and one of the Nose also has a termination resistor built in. This is not typical but can happen; checking with the OEM or a known good source of information as needed.
• If you think you have a Node Not communicating on the Bus test the wiring at this point.
o Back probe the suspect Node’s connector on the CAN High and Low wires for resistance.
 Do you have the same reading 60Ω reading as before on the main Bus?
• Yes (Confirm pin and socket connection tension and connectivity. Bus is not your issue.
• No (Remove the Neg. lead from CAN Lo and connect to the CAN Lo of a different Node, Did this restore the 60Ω reading. If yes find the open in the CAN Lo wire to that node. Use the same test procedure for the CAN High wire.
• Connect DMM negative lead to a good body ground. Then test both CAN High and Low wires for shorts to vehicle body. Most systems will read in the KΩ
• Reconnect the Vehicle Battery.
• Connect DMM negative lead to Battery Negative. Then test both CAN High and Low wires for shorts to Battery Negative. Most systems will read in the KΩ
• Connect DMM negative lead Battery Positive. Then test both CAN High and Low wires for shorts to Battery positive. Most systems will read in the KΩ
Testing the CAN Bus wiring integrity CANNOT BE OVERSTATED and requires the use of a DMM. Wire integrity/ continuity are a must. I personally use the Min/Max function when wiggle test the harness because it alarms if the resistance reading changes.

DSO:
Digital Storage Oscilloscope is an invaluable tool when working on CAN Bus. It lets us see the Bus signals and we can confirm very quickly if the signals are as they should be. We can see signal deformity and glitches but it is not a replacement for the DMM. Using all three together (Scan Tool, DMM, and DSO) will make troubleshooting the CAN Network easier by far.
A personal note regarding using a DSO, I have traces sent to me most days and they all have the same issue. Low sample rate and short time base. Not enough information to make a determination.
1. Increasing the Sample rate cost nothing! Crank it to the Max!!!!!!
2. Turn off all filters and math channels while recording; add them later if needed.
3. Increasing the Time per division. Stop looking at the signal when recording it. Use the DSO as it should be, use Seconds or Minutes per division not milliseconds.
4. Once recorded use the horizontal zoom.
5. Then if needed go back and get the detailed trace if needed.
I use the Pico Automotive 4 channel scope for its ability to do deep recordings and zoom capability. The software works great and has a lot of need tools. The software is free and downloadable, this allows file sharing with others who may not have a Pico but need to review the recorded files.

Please keep in mind this is just an overview and much more then I intended on writing.


If you would like to know the history of CAN Bus please take the time to read the vast amount of information on the Web.

Iver
TwoWaves
TwoWaves
Posts: 182
Joined: Mon May 27, 2019 2:55 pm

Re: CanBus on Transit Custom

Post by Iver »

if you would like to know the history of CAN Bus please take the time to read the vast amount of information on the Web
Why bother, its been around since 1991 / 92 ? in cars. Old news!

Shimano use to change gears on a push bike !

Not difficult to understand & fix issues with it, easier than replacing brake pads ! (Never spending half a day looking for the Locking wheel nut key)

K444LUN
Newbie
Posts: 1
Joined: Sat Oct 26, 2019 6:50 am

Re: CanBus on Transit Custom

Post by K444LUN »

Hi, hope you can help me out? did sort out the transit with abs, traction control, airbag light and speedo not working? my 2013 2.2 custom is the same but hasn't gone to limp mode (yet!) drives absolutely fine otherwise. thanks

Jamieg2010
Newbie
Posts: 1
Joined: Fri Mar 27, 2020 10:06 am

Re: CanBus on Transit Custom

Post by Jamieg2010 »

Hi did anyone get to the bottom of the no cluster /loss of power fault got the same problem and can’t get to the bottom of it

User avatar
FioranoCars
TwoWaves
TwoWaves
Posts: 386
Joined: Thu Dec 13, 2012 11:26 am
Location: London, UK

Re: CanBus on Transit Custom

Post by FioranoCars »

Jamieg2010 wrote:
Fri Mar 27, 2020 10:09 am
Hi did anyone get to the bottom of the no cluster /loss of power fault got the same problem and can’t get to the bottom of it
Hi Jamie
I think the moral of the story with CAN-BUS or any other fault is that there are no silver bullets, and that testing, not guessing, is the only way to go!

Now I fully understand your request for guidance seeing possibly similar symptoms here and that is always a good thing, but without knowing your exact symptoms and the tests you have done, then it's hard to give specific advice ... is it intermittent or relatively constant? etc

I would start by checking the body control ECU and the main cables feeding it, wiggle testng while using the scope to monitor CAN signals, most of these issues seem to be from oxidised connectors or chaffed cables, often in the back of the plugs (inter connectors as well as ECU plugs etc).

I've seen 4-5 in the last 3 years, all slightly different, so no "one-fix". Do some testing and narrow the symptoms and rule in/out various options.


Use an accurate wiring diagram and network topology to find commonality points for the issues, to help focus your testing.

Post your specific issue with what you've done (with captures showing the issue - so we can see if it's short to ground, open, short together etc etc) as well as wiring resources, and people will often invest huge amounts of time to review and help you. We are in this together, now more than ever.

Stay safe during these troubling times and good luck, hope to hear more and help you further
Best
Richard

Post Reply