Alright, I'm fairly new to the OBD-II scene so I have a few questions for a project I'd like to work on. It involves controlling my windows, doors, engine, etc. thru the OBD-II by reverse engineering.
I realize that there are public messages and manufacturer specific messages that are broadcast across the OBD-II.
- Are the manufacturer specific messages broadcast always or must you request them? (do those cheap scanners on the net also scan the manufacturer specific codes as well? or will i need to implement my own device)
- Are these messages transmitted with all interfaces? CAN, J1850 VPW, PWM, etc. or will I only be able to get my desired functionality through CAN?
Got any advice?
btw, I'd like this to work across all the interfaces b/c me and my buddies dont all own the same car =)
-tryp
What you are talking about is completely manufacturer specific.
For instance in an Audi you can only do this stuff if the car supports CAN. That only started around 2004, and only in specific models.
The interface and protocols, and supported features will be different for every make and model of car.
so i'm guessing my project is possible but can anyone specifically answer my questions?
-tryp
The answer to all of your questions is: It is all manufacturer, make, and model specific.Originally Posted by tryptophan
The poster above is correct -- what you're trying to do is REALLY manufacturer-specific, but I can try to answer.
The most common techniques are command-response (mode 22) or continuous data stream (mode 2A). Neither Ford nor GM actually does them as described in J2190 so don't waste your time.
In some cases you could sniff data that's broadcast on the bus. For example, GM you often see the Engine talking to the Transmission or the instrument cluster. In that case you could utilize the same data (speed, etc) assuming you understood the message. On the other hand, the last 300C I saw had a gateway/firewall so there was no idle traffic visible on the OBD2 connector.
Most cheap scanners don't do manufacturer-specific parameters, because it costs a LOT to license the data ($10k per year plus fees for each OEM) or perhaps more in time/effort to reverse engineer. Even if you found a cheap scanner, it sounds like you want a fully-integrated solution for your CarPC so you're probably going to have to do some programming.
On my Mustang it looks like the power windows use a hardwired switch that cannot be controlled over the network. In that case it's not an issue of network protocol -- it's just oldschool electronics. What you're asking is not correlated with the network protocol.
When you ask about device control (power windows, etc) these are unpublished and completely different for each automaker. Often it's even different between vehicles since there are a few different tier1 electronic module suppliers. You can either join the scantool industry and pay for the data or obtain a few factory scantools and start reverse engineering.
thanks for your responses and i realize it is make/model specific. i'm just more interested in if this is even possible.
Well what i was trying to get at was whether or not i could just use an ELM or a scanner on the net to just receive the manufacturer specific codes. I don't really care if these cheap tools can understand them, but atleast give them to me. I'll then find my own way to interpret them? Are there scanners out there that will just give me all the codes on the bus?
You also have to take into account that most of what you are trying to do, if it is supported, is not going to be sent over the OBDII port. Audi's for instance have a multimedia and central convience CAN bus. To get access to it you have to tap the wires in the back of the instrument cluster.
What you need to do is find out what types of cars you want to supoprt, and then start figuring out if any of the systems you want to control do have a centralized data bus. After that you would figure out how to communicate with them.
I'd say assuming that the tool implements the protocol correctly (and that's a huge assumption with cheap equipment), then sure it can send and receive "anything" with very few exceptions. It's all just bits and bytes on the network wire.
But I mentioned a few exceptions. On an older Ford (PWM) it's more difficult to monitor unfiltered network traffic. Most cheap cables are too slow to interact with an unfiltered network, and many don't let you adjust important settings. You're unlikely to get J1850 IFRs, Chrysler SCI support, or maybe even ISO15765 29-Bit. Some older tools don't even give you direct control over the address and headers.
"It might work, depending on the vehicle". Some only need simple features, others may expose bugs/problems in low-end equipment.
OP what you mentioned about opening windows, like everyone said it's car specific but if you wanted an example on how to sniff messages using a cheap scantool take a look at this page
http://www.obdpros.com/resources.php
Download the OBDPro datasheet it shows and example of opening windows on a 1996 Chevy Trailblzer using the OBDPro scantool. Although the trailblazer uses CAN for the OBD Protocol it is still using CLASS II messages for other controls and you can sniff the messages and figure out what message opens the window
wheres the link for the datasheet?
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