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OBD Scanners Discussions on using On Board Diagnostic (OBD) scanners/ Diagnostic Equipment related to TDIs

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Old December 12th, 2013, 20:31   #1
macoombi
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Default Running two devices from OBDII port??

Anyone tried using a y-splitter cable on the OBDII port to run two devices at the same time?

I've got a new insurance nanny device and I'd like to run something like a scangauge or Car Chip at the same time. Wonder if this is possible on my '02?
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Old December 12th, 2013, 20:33   #2
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Yup. Works fine.
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Old December 12th, 2013, 20:35   #3
macoombi
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Found my own answer here:
http://forums.tdiclub.com/showthread.php?t=308987

Now I just need to find out if the nanny device actually communicates with the PCM or if it's just using the power from it. Apparently it does contain an accelerometer and a GPS.
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Old December 13th, 2013, 00:32   #4
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Seconded. Run my scan gage and VCDS using a Y cable. I think those nannies just pull power. Take a look at how many pins it has. if only 2, its power. I doubt it 'speaks' german.
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Old December 13th, 2013, 05:21   #5
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I'm confused. This thread says yes it's fine. The linked thread says no it's not fine.
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Old December 13th, 2013, 06:16   #6
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It doesn't work for me... well kind of. I run SGII full time and was tired of having to unplug it for the sake of VCDS. Also, the SGII connector was a little fiddly to get on/off sometimes. I ended up getting a Y-Cord and it appears only one device can grab the line at a time, for me anyways. Whether the car's running or not, plugging VCDS into the 2nd port results in one of the two working, the other not. I can 'steal' the port from SGII using VCDS setup menu by testing the connection then saving but only sometimes. Other times it may take a couple tries. SGII will go blank when successful.

KWP protocols are pretty timing sensitive and if two devices are bombarding the ECU w/requests, things could get messy. Both devices will get all requested data regardless. When done, unplugging VCDS does not restore the display on SGII. I have to hit the menu button on SGII and then it re-establishes communication without further fiddling.

Dunno if CANBUS will handle this better. Could be on later model VW's two or more devices could play together just fine. Not so much on my older Mk4.
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Old December 13th, 2013, 09:17   #7
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Here is the issue. All OBDII communications must go through the CAN gateway. The CAN gateway can only handle one instruction at a time. It is possible to plug 2 devices into the connector with a "Y" cable. However, there will be problems if both devices try to talk to the car at the exact same time. The CAN gateway has no way to know that there are 2 devices, so it cannot address only one to send data to only one device. As long as one of the 2 devices is relatively quiet (not constantly demanding info), both devices will probably work OK. However, if one of the devices is polling for data constantly (like the Torque App running 6 gauges), I would not expect any other device to reliably communicate.

In other words, 2 devices can be plugged in at the same time, but they might not both work as intended. For any important function, I would not recommend plugging 2 devices in at the same time.

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