CAN bus speed

[Remittub]

Hi,  First of all. I assume my Mark 2 57 plate Focus has a CAN bus - yes ?  ( I am trying to get my Arduino based code reader to connect to the bus) Does anybody know what speed  the bus runs at ? (My Sparkfun Arduino shield offers 3 alternaive settings 125kb/sec, 250 kb/sec or 500 kb/sec) Any help would be appreciated !!

[isetta]

I don't know the answer but I am pretty sure tdci-peter has mentioned it at some point in posts where he has answered stuff about canbus problems on mk2 focus (I am sure he was comparing the slowness of it compared to computer usb speeds). I have always found it difficult using the search function on this forum.

[isetta]

actually there are two CAn Buses on these cars. the higher speed one for the engine ecu and the lower speed one for the body control module built into the fusebox  (I think)

[JW1982]

HS (High Speed) CANbus has a network speed of 500 Kbps

MS (Medium Speed) CANbus has a network speed of 125 Kbps

 

On newer Ford models there is also MM (MultiMedia) CANbus. The MM CANbus network is connected to both the HS and MS CANbus networks by a gateway. The MM CANbus network can be accessed from both the HS and MS CANbus network.

[Remittub]

So, are both CAN busses accessible from the socket under the steering wheel ?   If so, how do I know what speed to use ?  Many thanks for the replies by the way !!

[isetta]

yes they are both on the same OBD socket. 

when you buy a fault code reader with a switch on like these here:

https://tunnelrat-electronics.fwscart.com/

the switch alters which pins the code reader electronics are connected to. 

if you have a more basic code reader it will just connect to the high speed canbus

 

 

[Remittub]

I thought that CAN was only on two pins (CAN-H on 6 and CAN-L on 14) ?  But my question is how does the tester know what rate to use to access the high or low rate CAN bus ?  If I have understood this correctly, most of the useful stuff is on the high rate CAN, so I guess (from JW1928's info) that I should use 500 kb/sec.

[isetta]

As far as I know engine stuff is high speed canbus, other stuff like airbags etc is on ms canbus . The ms canbus is on two different pins in same socket, cant recall which pins. Some pins are standard for all makes of car, other pins are used differently by other car makes.

[Remittub]

Ah ..... !! Different pins !

Found some info on MSCAN-H and MSCAN-L here  https://forscan.org/forum/viewtopic.php?t=4

MSCAN-H is pin 3 (as opposed to pin 6 for HSCAN-H)

MSCAN-L is pin 11 (as opposed to pin 14 for HSCAN-L)

MSCAN runs at 125kb/sec whereas HSCAN runs at 500kb/sec

Think that I know where I'm going now - thanks to all !!