SL/R230: CAN BUS Anyone help with scope waveforms?
Thread Starter
Newbie
Joined: Jul 2017
Posts: 14
Likes: 3
From: Sunny North Wales
SL55 AMG
CAN BUS Anyone help with scope waveforms?
Continuing with my ESM P1925 Drive Authorisation fault
What should the waveforms look like?
There seems to be very little info on this.
I have a dual trace oscilloscope and have done some probing on the brown CAN pairs and the Wakeup Green pairs.
DC volts checks are pretty normal and can be seen changing after couple of minutes to the sleep state.
Also if I were to power up the ESM on a bench would I expect to see CANBUS waveforms on pin 6 and 7 of the ESM PCB or is that comms only generated from the EIS key module?
Thanks in advance
What should the waveforms look like?
There seems to be very little info on this.
I have a dual trace oscilloscope and have done some probing on the brown CAN pairs and the Wakeup Green pairs.
DC volts checks are pretty normal and can be seen changing after couple of minutes to the sleep state.
Also if I were to power up the ESM on a bench would I expect to see CANBUS waveforms on pin 6 and 7 of the ESM PCB or is that comms only generated from the EIS key module?
Thanks in advance
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
Check out pages 11-14 of this CAN training document for details on the CAN message wave forms, Jules.
The ESM is on the drivetrain CAN, and any module can put a message onto the CAN for other modules to read.
The ESM is on the drivetrain CAN, and any module can put a message onto the CAN for other modules to read.
Thread Starter
Newbie
Joined: Jul 2017
Posts: 14
Likes: 3
From: Sunny North Wales
SL55 AMG
Check out pages 11-14 of this CAN training document for details on the CAN message wave forms, Jules.
The ESM is on the drivetrain CAN, and any module can put a message onto the CAN for other modules to read.
The ESM is on the drivetrain CAN, and any module can put a message onto the CAN for other modules to read.
Thanks for that.
Now I'm not sure if I've found something odd with my CAN B (Brown pairs) in that I've always assumed a CANBUS network should have termination resistors at either end.
My CAN C (Green pairs) measure 60 ohms but the Brown Pairs measure infinity between LO and HI.
Can someone confirm if this is correct?
I've measured at the Rear SAM and passenger sill X30/15.
Same infinity reading at both ends 🤔
Rear battery disconnect of course
Thread Starter
Newbie
Joined: Jul 2017
Posts: 14
Likes: 3
From: Sunny North Wales
SL55 AMG
Double checked again and brown pairs have no network resistance ie open circuit.
Measured at the EIS N73 key switch pins and open circuit.
My virtual Star diagrams don't indicate which modules the resistors are in? Anyone know ?
Like I say CAN C measures 60 ohms
CAN B is open circuit.
Or am I on a goose chase here?!
Measured at the EIS N73 key switch pins and open circuit.
My virtual Star diagrams don't indicate which modules the resistors are in? Anyone know ?
Like I say CAN C measures 60 ohms
CAN B is open circuit.
Or am I on a goose chase here?!
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
In engineering parlance CAN is a transmission line. In practice, generally a terminating resistance is required at each end of the line. With CAN the value is 120 ohms. The need for resistances is dependent upon both the length of the line and the communication rate, with longer lines and faster rates requiring the resistances.
Looking at how the CAN is wired in an R230, I can not discern where there is a beginning or an end to the line. So I do not know the answer to your question. But in the case of the body CAN, your measurement suggests to me that there are no resistances; because if there were, then this would require two to be missing, and that seems very unlikely to me.
At any rate, if there are communication issues on the body CAN, then I don't see how this would have any bearing on your issue with the gear selection module.
At any rate, if there are communication issues on the body CAN, then I don't see how this would have any bearing on your issue with the gear selection module.
Thread Starter
Newbie
Joined: Jul 2017
Posts: 14
Likes: 3
From: Sunny North Wales
SL55 AMG
That's my thoughts exactly it's unlikely 2 resistors are missing.
However according to CAN networks principles of operation they require resistors to reduce signal bounce and interference, and to "prevent the signal getting damaged" was in one article.
I'm amazed this hasn't been raised before with the 230?!
But it sounds like Mercedes hasn't put resistance in CAN B, or have they?
Unless someone can confirm this on their working car for me , we'll never know?
It would take 5 minutes to access the rear SAM and take a measurement for me 😎
Maybe someone has got their 230 already in pieces ?
However according to CAN networks principles of operation they require resistors to reduce signal bounce and interference, and to "prevent the signal getting damaged" was in one article.
I'm amazed this hasn't been raised before with the 230?!
But it sounds like Mercedes hasn't put resistance in CAN B, or have they?
Unless someone can confirm this on their working car for me , we'll never know?
It would take 5 minutes to access the rear SAM and take a measurement for me 😎
Maybe someone has got their 230 already in pieces ?
Trending Topics
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
This thread hasn't got many people reading it, so there may be no answer for a while.
MB World Stories
The Best of Mercedes & AMG
Dubai Tuner Gives the Mercedes G-Class An Entirely New Look
Verdad Gallardo
Six Gift Ideas Your AMG Loving Dad or Grad Will Cherish
7 Craziest Things AMG Gas Ever Built
Verdad Gallardo
New Electric Mercedes-AMG GT 4-Door Coupe Unveiled: 10 Things You Need to Know
Verdad Gallardo
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
