can bus connector problem

irideforlife

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Jan 8, 2009
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15
I have a 99 W210 with the ever increasing electric problem inside. Seats, windows etc. I have located the can bus connector near the A pillar and pulled it out, small connector block in brown. I wanted to start removing each one over a period of time to try to find the problematic module as this is what I have been told to do but I could not get the first plug out and eventually it broke. O dear, what to do now? the part that has broke is the small plug holding the first two wires. Any advice please regarding repair and how to remove the rest?
 

Zulu 10

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Sep 21, 2013
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Car
R171 SLK200, W203 C220CDI
Do bear in mind that if you disconnect CAN Bus modules then the cables must be suitably terminated in order to avoid mismatches which may cause further/different problems.

All connector shell and pin/socket part numbers are contained in the M-B Electronic Parts Catalogue - there are plenty of downloads available on the web, usually bundled with WIS.
 
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irideforlife

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Jan 8, 2009
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I didn't understand a word of that sorry. Sufficiently terminated means?
 

Zulu 10

Active Member
Joined
Sep 21, 2013
Messages
85
Car
R171 SLK200, W203 C220CDI
A CAN Bus is treated as a 'transmission line' which means that the signal should propagate along it whilst 'seeing' a consistent load impedance between CAN-High and CAN-Low wires.

Wherever the impedance changes, depending on the size of the difference, and the 'sudden-ness' of the change, a percentage of the original signal will be reflected back the way it came.

If for any design reason it is necessary to make a change then it should be done gradually and not as a step change.

(This is analogous to a stealth aircraft and the reason for some of the saw tooth panel edges, but I digress.)

In the case of an instantaneous open circuit or a short circuit, all the signal will be reflected.

This is what would happen if you simply pull the plug out of a CAN connected module: all the signal will be reflected back into the network.

In the case of the CAN network these reflections would/could cause interference with legitimate signals.

Therefore, to prevent this you should replace the disconnected module with a 120 Ohm resistor.

(If you struggle to find the connectors in EPC then reply with your VIN and I'll have a look for you)
 
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