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MasterOSkillio
Aug 27, 2003


I have a 2014 WRX that I have a few mods on (Cobb stage 2+/stiffer sway bars/STI brake swap/Grimmspeed intercooler/Grimmspeed air-oil separator/clutch,brake pedal brace). Overall I am very happy with the car and what I have done. One thing I was annoyed about was that there is a serious lack of info to the driver. I really wanted to see oil pressure, oil temp, water pressure, and boost as well, but I donít want to have gauges all over the place I am not a huge fan of gauge pod clusters. I found an insert that goes into my dash (the SMY Dual pod) this keeps the look much more stock and allowed me to install a Banks iDash multi gauge. The iDash is something that seems to be more for the pickup truck scene, but it works off of the CAN bus system to get basic info and power so it can be used for any modern OBDII car. It is nice because even if I am not looking at the iDash it will measure multiple inputs, and I can set a high/low alarm for anything that is being monitored and get warnings. Obviously in this way if something small happens I can know and turn off the engine before itís a big problem (over boost, oil pressure/temp high/low. ect)

The issue I have is that I the also have a hookup for my stereo that reads info from the CAN bus as well (TPMS, Engine air intake temp, speed, battery voltage, doors open or closed) and both of these devices donít like to work with each other. My original thought was that the iDash system was just looking at readouts from the ECU and displaying them on a gauge so that since it is only reading info they should work together. While I understand that you canít have two devices talking on the same bus at the same time I thought that if you have one device only listening that another could ďtalkĒ to the ECU with no issues and it would not be a problem. I was wrong, or the iDash is trying to talk to something when both devices are hooked up I get little or no readings or some messed up stuff happens. For now I am just running the iDash, but I was wondering if there was some device that might mimic a network switch or a repeater or something that designed for the CAN bus system might be able to let me use both devices. Is that possible at all?

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Safety Dance
Sep 10, 2007

Five degrees to starboard!



If it's wired correctly, a CAN device should be able to detect if it's talking over another device, and both devices should resolve the conflict. I don't think there's such a thing as a CAN network switch.

SNiPER_Magnum
Jan 21, 2001

Don't close. Don't close.




Nap Ghost

Many devices are already on the same network together. The CAN communication protocol has a built in way of dealing with message conflicts. It should not be a problem with your two devices talking at the same time.

How is the iDash connected to CAN? Is your radio factory or using the factory radio CAN connection? The way you wire a CAN network affects impedance and can cause communication issues.

First thing: with all devices connected and key off, measure the resistance between CAN high and CAN low at the diagnostic port. Should be 60ohm.
Second: with key on, measure voltage between CAN high and ground, then CAN low and ground. Should be ~2.5V.

MasterOSkillio
Aug 27, 2003


SNiPER_Magnum posted:

Many devices are already on the same network together. The CAN communication protocol has a built in way of dealing with message conflicts. It should not be a problem with your two devices talking at the same time.

How is the iDash connected to CAN? Is your radio factory or using the factory radio CAN connection? The way you wire a CAN network affects impedance and can cause communication issues.

First thing: with all devices connected and key off, measure the resistance between CAN high and CAN low at the diagnostic port. Should be 60ohm.
Second: with key on, measure voltage between CAN high and ground, then CAN low and ground. Should be ~2.5V.

ok, I didn't realize that you could have multiple devices at once, I will break out the ammeter and check.

I should have mentioned the radio is an aftermarket kenwood unit I bought that connects to the OBDII port, but is powered on it's own circuit., the iDash is also connected via OBDII there is a splitter that lets them share the port.

SNiPER_Magnum
Jan 21, 2001

Don't close. Don't close.




Nap Ghost

That's your problem. You can't use a splitter to Y stuff together like that. You're going to need another way to connect at least one of those to the CAN.

Here's how a CAN network should look:

It's arranged as a backbone, and each device or node is a stub that taps off the backbone. The OBDII port is an empty node. If you look closely, you can see each node is actually a Y off the backbone, so Y-ing off a node is actually a double Y which screws up the network. You need to add another stub to the backbone somehow.

BlackMK4
Aug 23, 2006

wat.

Megamarm

I think what Sniper is describing is what is called a canbus hub

SNiPER_Magnum
Jan 21, 2001

Don't close. Don't close.




Nap Ghost

Do you mean one of those passive hubs that have a series of connectors on a common bus? I don't think that will help if he's having problems with a splitter since they'll be doing essentially the same function. I meant finding an unused stub. Maybe the factory radio had CAN that an aftermarket wiring kit didn't use. Or if the wiring harness is common between manual and automatic, and the transmission CAN stub is unused. Or if you are good with wiring, cut into your harness and splice in your own new stub (do not do this unless you are sure of what you are doing or the rest of your car might stop working too).

taqueso
Mar 8, 2004


:911:
:wookie: :thermidor: :wookie:
:dehumanize:

:pirate::hf::tinfoil:


You can replace a device on the existing net as a check. Just make sure you maintain termination if you replace a node that is terminated and don't add extra either.

Correct termination is vital.

If I remember correctly, the can spec has info on sub branches and tree topologies, they are possible.

Commodore_64
Feb 16, 2011

love thy likpa



You might check the input with an ohm meter, in case one of your two devices is so ineptly designed it overterminates the bus.

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Solosilent
Dec 16, 2005


Are both devices generic that can be hooked up to any vehicle or are they specific to your model year vehicle? There's no common CAN messaging between the different OEMs. If they are generic and can be plugged into any vehicle and display data they are likely requesting OBD2 PIDs for their data, rather than just monitoring bus traffic. These OBD2 and responses from the vehicle will be on the same message ID and will probably confuse the two devices. Does the rest of the vehicle wig out when they're both plugged in? If the rest of the car is fine, I don't think there's a CAN wiring/termination issue, just a problem with the two extra devices.

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