Can the OBD2 port feed 2 devices?

[Turbo]

Wondering if anyone here has had success using the OBD2 port to feed 2 devices simultaneously?


Currently I have a very fast bluetooth OBD2 scanner hooked up to the port, and that data is being read by RaceChrono.

I would also like to utilize the OBD2 data-stream to supply a digital dash like an AIM or Racepak for display purposes while I'm driving.


I know they make OBD2 'y' connectors that split the one port into 2, but what I don't know is whether this will allow 2 devices to access the ECU data at the same time.


Would love to hear from anyone who has some experience or thoughts on this.

[sharpsicle]

From what I've been told on CAN bus systems, they will interfere with each other if both devices attempt to pull data simultaneously.

[UT_BRZ]

I installed an Alpine ILX-207 with the idatalink maestro unit to run gauges on the head unit. I have it connected to the port behind the head unit near the glovebox. Whenever I have had to collect data for tuning with the Ecutek, it will force me to disable info on the head unit. I'm not familiar with the programs you are attempting to use, but it's only one or the other with my setup.

The idatalink setup is pretty awesome as it pulls and displays a lot more gauges as well as reads any CEL codes. You are also able to reset the codes from the head unit itself.

[ermax]

Yes you can run 2 devices but it depends on what they are doing. I log with my Tactrix while also having a Raspberry Pi connected and watching for specific packets at the same time. The Y cables are cheap, give it a shot. The only warning I would give is unplug other devices when flashing the ECU because it will need exclusive access while flashing and you don't want to have a failed flash.

[mabviper]

You can connect multiple devices on the OBD2 bus so long as only 1 device is sending out packets to the car. You can have 1 OBD2 reader (it'll send and receive) and 1 passive canbus reader (only receive) and it'll work. However, if you have 2 OBD2 readers, it won't work since both will try to actively send and receive packets from the car.

In your application, I don't believe it'll work. I do not think an AIM or Racepak is 100% passive. I do believe they query the car for data. If you want do use both of these, I would connect your ODB2 reader to the OBD2 port and hardwire the AIM or Racepak on the canbus connector behind the radio unit.

[ermax]

My Raspberry Pi sends and receives packets and doesn’t interfere with my Bluetooth adapter. OBD2 is basically an I2C bus so it’s designed for multiple devices talking at once. There are already a ton of devices talking over this bus without even plugging something into the OBD2 port. For example all the ECUs are talking, the cluster is talking, etc etc.

It’s amazing watching all the packets scroll on the console when monitoring the raw traffic on the bus.

[mabviper]

Not really sure what you mean that obd2 is I2C. The obd2 port on the car exposes canbus network but obd2 is a protocol that uses canbus. Listening to canbus traffic and querying obd2 is different. If you have 2 devices querying obd2, you may get some crosstalk. It's not harmful to the car cause it doesn't care where the request come from but your obd2 readers might misinterpret the responses.

Sent from my Nexus 6P using Tapatalk

[ermax]

My wording wasn’t that great. Yes OBD2 is a protocol that runs over CANbus which is much like i2c. It’s a serial bus were everything is addressed. I wouldn’t think two devices requesting the same PID at the same time would be that big of a problem because both devices would see the responses. It isn’t like one device gets the response and then removes it from the stream. I’ve run all kinds of combinations of devices on mine and it worked. I have had the software I wrote on my Raspberry Pi throw a CEL and go into limp mode. Haven’t been able to debug it because it only happens once every few months.

[Turbo]

Originally Posted by mabviper

In your application, I don't believe it'll work. I do not think an AIM or Racepak is 100% passive. I do believe they query the car for data.

If you want do use both of these, I would connect your ODB2 reader to the OBD2 port and hardwire the AIM or Racepak on the canbus connector behind the radio unit.

Please excuse me being a noob about all this, but how does hard wiring the Racepak that way allow the data stream to operate differently from having both connected to the OBD2 port via a Y-connector?


I had the idea of using a bluetooth receiver to connect my OBDLink LX OBD2 scanner to the Racepak (since I was pretty sure that scanner is capable of connecting to more then 1 device at a time) but was told by a Racepak user that Racepak doesn't have any way to do that.

[ermax]

Originally Posted by Turbo

Please excuse me being a noob about all this, but how does hard wiring the Racepak that way allow the data stream to operate differently from having both connected to the OBD2 port via a Y-connector?


I had the idea of using a bluetooth receiver to connect my OBDLink LX OBD2 scanner to the Racepak (since I was pretty sure that scanner is capable of connecting to more then 1 device at a time) but was told by a Racepak user that Racepak doesn't have any way to do that.

Some cars filter some of the CANbus traffic from the ODB2 port so if you want access to the raw traffic you have to tie directly to the CANbus network somewhere else. CANbus has to be terminated properly (120ohm if I recall). I'm not sure I would mess with tapping directly into it unless you know what you are doing.

[mabviper]

To be honest with you, you make a good point.

The OBD2 port in the car exposes raw canbus network. All OBD2 queries are done through canbus, ie OBD2 queries a number of computers in the car and those computers respond in OBD2 format. With respect to the canbus connector behind the radio, it connects to the exactly the same canbus network same as the OBD2 port connector. You can even send OBD2 commands there and it'll be ok. Raw, unfiltered canbus traffic is available in both connections. The car only has 1 canbus network unlike some vehicles that may have 2 or more, critical and non critical networks.

Back to your point, using a splitter or connecting to the aux canbus connector will result in the same thing. My suggestion wasn't correct.

In theory, both devices should work independently. However, you might get in some scenarios that device 1 asks for something and both device 1 and device 2 process it, with device 2 thinking the message is for itself. This example with happen when you try to query oil temperature. Oil temps queries are done by in 2 stages, main query and a followup query. How your devices handle this and potentially many more queries like this may result in them working or not working.

You also have to keep in mind the query rate of devices. If device 1 queries at 100Hz and device 2 queries at 100Hz per channel, what will the OBD2 computer do? Do you really want to flood the canbus network considering other computers like VSC module communicates in this network?

Anyways, I suggest just dealing with 1 device unless you can 100% guarantee that the 2nd device is purely passive and does not send queries to the network. Get an AIM Solo DL 2 if you have an Iphone. It has an app. Racelogic also has an app for Android. Racechrono has a way to receive car data through a specific format. However, I don't think either AIM or Racelogic really care about supporting something like Racechrono.

Originally Posted by Turbo

Please excuse me being a noob about all this, but how does hard wiring the Racepak that way allow the data stream to operate differently from having both connected to the OBD2 port via a Y-connector?


I had the idea of using a bluetooth receiver to connect my OBDLink LX OBD2 scanner to the Racepak (since I was pretty sure that scanner is capable of connecting to more then 1 device at a time) but was told by a Racepak user that Racepak doesn't have any way to do that.

[ermax]

Yeah in my experience with this car the OBD2 port doesn't seem to be filtered at all but I've never tapped into it anywhere else and compared the traffic between the two points. All I know is you can see non-OBD2 traffic on the OBD2 port which leads me to believe it's unfiltered.

Flooding the bus would be my concern too and I think flooding may be the reason I've gotten CELs on my car when ****ing around with my RPi. There are some cars with 1Mbit buses but ours is 500Kbit. But I've never really tried to measure what the actual utilization is. For all I know it's got tons of bandwidth left.

Oh one other thing I read in the Racepak manual is it says not to use an "OBD2 splitter".

[Turbo]

Originally Posted by ermax

Oh one other thing I read in the Racepak manual is it says not to use an "OBD2 splitter".

Well - this is probably the most damning thing given what I was trying to do


ok - so I will assume connecting to both RaceChrono AND a Racepak display dash via OBD2 is a 100% definite no-go.


That means I either need to feed the Racepak data from manually installed sensors, or else feed it via OBD2 and use a Racepak-supplied data-logger if I still want to do that.



....which leads me to 2 other questions:

- How accurate are the OE sensors reporting over Canbus (ie for water temps, oil temps, AFR and (I believe) EGTs ?

- If I install external manual sensors to hook up to the Racepak is there a way to calibrate them ?

[mabviper]

I've personally only dealt with AIM systems and you can calibrate any sensor you want. I'm sure Racepak has the same capabilities. The Vantage CL1 kit probably has what your want but it didn't save the data anywhere but the cloud. I'm assuming you have to pay for that.

Sent from my Nexus 6P using Tapatalk