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Old 02-12-2011, 05:20 AM   #1
Jeffreypang911
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Default CAN High/CAN Low

Anyone know what CAN High/CAN Low is from the OBD2 Connector plug for your scan tool does?

http://pinoutsguide.com/CarElectroni...s_pinout.shtml

Pin 14/16 on the connector.

Jeff
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Old 02-12-2011, 07:59 PM   #2
Matt L
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CAN low is usually about 2.4v and CAN high 2.6v
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Old 02-12-2011, 08:55 PM   #3
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I don't get the question, can you be more specific?

Canh and canl both carry the same signal,usually at a slight voltage offset , done for redundancy, both carry data between computers on the car and are coupled at each " end" by 120ohm resistors. Take an ecu without termination resistors out the network and the network lives, take both ( and sometimes one) ecu out the network with the termination resistor and the network dies.

More complicated on some cars as if a fault is detected ( short to earth or short to live) the suspect part of the network is removed by isolation relays. That's about it in the physical sence.
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Old 02-12-2011, 09:27 PM   #4
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Try http://en.wikipedia.org/wiki/Controller_Area_Network

Last edited by Laurence; 02-12-2011 at 09:31 PM.
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Old 03-12-2011, 01:25 AM   #5
Jeffreypang911
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I was playing around with the wiring, and I must have accidently cut the CAN Low wire going to the back of the OBD2 scanner port (light blue). It does not go back to the ECU like the CAN Hi so I am trying to get more information on it, kind of confused that it doesn't go back to the ECU so I am questioning if I need that wire or not.

From the following webpage:
http://digital.ni.com/public.nsf/all...256C1C006BE6AE

"High Speed CAN offers baud rates from 40 Kbit/s to 1 Mbit/sec, depending on cable length. This is the most popular standard for the physical layer, since it allows for simple cable connection between devices. This is the physical standard used in the DeviceNet and CANopen specifications. High speed CAN networks are terminated with 120 Ohms on each end of the network.

Low Speed/Fault Tolerant CAN offers baud rates from 40 Kbit/s to 125 Kbits/sec. This standard allows CAN bus communication to continue in case of a wiring failure on the CAN bus lines. In low speed/fault tolerant CAN networks, each device has its own termination. "

Does this mean the CAN Low operates as a back up in case CAN Hi fails? Am I searching in the wrong direction? Excuse my lack of knowledge, this is the area where I am the weakest.

Hope the clears things up a bit?

Thanks,
Jeff

Last edited by Jeffreypang911; 03-12-2011 at 01:28 AM.
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