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can bus ?

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8 years 10 months ago - 8 years 10 months ago #6951 by motamanacanic
can bus ? was created by motamanacanic
i have a merc slk in today problems with the can signals
can high and can low flat-lining,and not waking up on ignition or runing, no matter where i check !
any ideas before i start disconnecting control units and keep checking the signals
as i go as this takes a lot of time, checked verus scope on other cars and all ok ????
thanks


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Last edit: 8 years 10 months ago by Dylan. Reason: Adding attachment

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8 years 10 months ago #6953 by Ben
Replied by Ben on topic Re:can bus ?
Does your service manager hate you or what ?!?

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8 years 10 months ago - 8 years 10 months ago #6954 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic can bus ?
Only way I know is uncouple the modules one by one but you have to know which units have the 120 ohm terminating resistors as unplugging those brings the whole bus down.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Last edit: 8 years 10 months ago by Andy.MacFadyen.

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8 years 10 months ago #6975 by Dylan
Replied by Dylan on topic can bus ?
Deleted the other one since it was a double post. I'll add the attachment, funny picture :)

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8 years 10 months ago #6990 by Tyler
Replied by Tyler on topic can bus ?

motamanacanic wrote: i have a merc slk in today problems with the can signals
can high and can low flat-lining,and not waking up on ignition or runing, no matter where i check !
any ideas before i start disconnecting control units and keep checking the signals
as i go as this takes a lot of time, checked verus scope on other cars and all ok ????
thanks



Bwahahaha :lol:

Are your high and low flat lined at 0V, or 2.5V? 0V would suggest a short to ground somewhere. I'd start with some resistance testing at the DLC. Find your network pins, turn the key off, and measure resistance between both pins. Should be 60-ish ohms. Then check each individual pin for resistance to ground. Both should show OL or high megaohm readings.

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8 years 9 months ago #7220 by Gary B
Replied by Gary B on topic can bus ?

Tyler wrote:
Are your high and low flat lined at 0V, or 2.5V? 0V would suggest a short to ground somewhere. I'd start with some resistance testing at the DLC. Find your network pins, turn the key off, and measure resistance between both pins. Should be 60-ish ohms. Then check each individual pin for resistance to ground. Both should show OL or high megaohm readings.


I just went thru this with the Equinox, I saw that the power steering module was right by the DLC so I unplugged it and watched for the resistancd to rise to 120 ohms, then went module by module unplugging and plugging in again, till I got to the end of line resistor, which for that one was just behind the fuel tank, I left it unplugged and worked my way up to the ECM which serves as the EOL resistor for that end, with both EOL resistors off I think it read like 9 or 10 ohms between both pins.

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