Hiya, I have a 1998 Mk2 1.8iS, and I’ve always been disappointed at the lack of an OBD2 port, however I was recently looking at a wiring diagram for the US model 1996 (and thus Mk1) MX-5 and I noticed it seemed to include a second DLC connector (which should be OBD2 for a 1996 US car) as well as the under-bonnet DLC connector, and saw they were straight through connectors, no interface electronics - the old OBD header simply exposes more signals from other modules. Assuming the ECU firmware is the same (why wouldn’t it be), I’m wondering if my car could support an adapter cable. A few posts on this forum have mentioned the presence of serial lines on the header, so that gives me some hope. I found this manual for a OBD diagnostics tool:
It shows various connections and maps directly to OBD2 usage, so I’m wondering if anybody can confirm these, or tried to access the serial lines? I have no wiring diagrams for my car so I don’t know which pins are populated (although all 17 have a metal tag, obviously I can’t see underneath), has anybody tried anything similar or have the information to tell if it’s worth trying?
Sadly not I tried a couple of small experiments, first connecting an oscilliscope to the TEN, MEN and FEN lines on the diagnosis header, but there was no digital signal on any of them. It’s possible some sort of signal is required to tell the computer that equipment is present, but without knowing what the signal is obviously not much can be done about that. In case the ‘I’m here’ signal was the same as OBD2 I actually borrowed an OBD2 reader and temporarily wired it in using the info from the PDF I found, but it couldn’t detect anything, so no luck there.
Some people on miata.net had worked on reverse engineering the mark 1 ECU so I asked them if there was any evidence of serial port use, and they reported that the ROM didn’t appear to make use of the on-chip serial module - however, I’ve been thinking about that and it’s quite possible that if Mazda wanted to include a serial function, they’d want their own protocol (to make it easier to tie in dealers to their hardware) instead of using RS232, which is what the on-chip module probably does, so it may be they’re manipulating a pin on the CPU manually.
I’m not really sure what I’ll try next, I’m sort of losing hope of using the connector for anything useful, and wonder if maybe I should just buy a new car with OBD2 built in One unlikely notion I had wsa to find an emulator for the relevant CPU online and try to set it up to run the mark 1’s ROM (faking timing signals/etc.) and see if any likely areas could be identified.
I don’t really understand all the tech jargon you are using, but if it’s any help the ECU on your car will transmit live data (PID’s) to a Mazda diagnostic tool.
I’m puzzled because, although my MX 5 is a 2002 RS JDM model, it doesn’t appear to have an OBD port of any style, anywhere! It does have a grey adaptor marked ‘DIAGNOSIS’ on the left hand wheel arch in the engine bay with 11 of the pins connected. This sounds reminiscent of the NA diagnostics connector I’ve read about. However, as I undersatnd it the original OBD system had been available on much earlier MX-5’s.
I’ve searched the 'net looking for some information on this in vain! Any ideas?
That’s the header I’ve got too - I think here in 2002 the cars moved over to OBD2, but mine is a 1998 model so years off having that My original post erroneously said all the holes in the header were populated but I was mis-remembering, it’s only a few (e.g. the ones I’ve tried to experiment with ) But yes, the DIAGNOSIS port under the bonnet at the left is the one I’ve been experimenting with. There’s info that it can support both the “blinky LED” diagnostics (which I’m not interested in) and more informative data streams (which I’ve Googled extensively, found references to but no real info).
If there’s any chance your car is OBD2 though it might be you just need to find the ‘lost’ header - I did read one forum post somewhere on the internet where the guy had to search for ages before he found it - it had been kicked by a previous owner, and the plastic mounts and cracked, and the now free-floating OBD2 header had drifted up inside the dashboard. The guy had to rummage around inside the dashboard wiring to find it
This are exactly what I want, do you have any more info on this? The DIAGNOSIS connector, right? Do you have any info on this? Particularly, what the Mazda diagnostic tool does to make the ECU send the info, and ideally the format of the info itself
If I had a Mazda diagnostic tool it’d be easy to sniff the lines, but I can’t imagine anyone having one, particularly that I’d be able to use for a few days…
mazdad, on UK cars the EOBD (16 pin) connector is behind the fuse box cover in the dash.
Electric Monk - Yes the DIAGNOSIS connector has a K-line for 2 way communication with what Mazda called the New Generation Star (NGS) tester. This was later changed to a WDS (Worldwide Diagnostic System) and is now called an M-MDS (Mazda Modular Diagnostic System) which is essentially a Panasonic Toughbook with a VCM (Vehicle Communication Module).
Roadster Robbie, thanks for that extra info - the K-line is the same roughly as that in the OBD2 connector? From that original PDF I think the pin I used on the OBD2 tool I borrowed was the wrong one, so it’s not surprising my experiment failed Either way, if it’s the case then my hope is restored The wiring harness for the US NB did show pins to both OBD2 and DIAGNOSIS headers, but it didn’t make it clear which specific pins they went to (which to me seems kind of useless). Sadly i don’t have access to that OBD2 tool anymore but I could possibly build a circuit to experiment. As a guess I’d say MEN will be a K-Line (for Monitor ENgine? The others being FEN and TEN. I believe FEN is the blinky light and TEN triggers it - L-Line?) Certainly some potential for experimentation anyway You wouldn’t happen to know any more specifics about which pin the K-line is on? Does it obey the same standard as OBD2 (the ISO ones) or anything else documented somewhere I could design a circuit/write some code based upon?
mazdad, it definitely sounds like we’re looking for the same thing I don’t think I’d bother making an OBD2 adapter though, just go straight to a serial or USB interface. My eventual goal is for an integrated carputer so I can control that side of the software too
Do you have the cable + software to make it work too? If so, that could potentially be all I need to reverse engineer the protocol. I’d be happy to borrow it/send it back, if it helps me get there (hopefully it’s a relatively straightforward protocol. The software could potentially also make it easy, as I could possibly detect what the software did vs. what the protocol did)
Otherwise, I’d probably only be able to take it apart and see what was inside. Wiring it (manually) to a car might be enough to see it do some handshaking, but that’s all getting a bit risky/destructive, so I wouldn’t like to do it to a borrowed one. I’d happily buy one for $30 or so for myself so perhaps I can try bidding on that one
I in fact, have a New Generation Star tester which the card plugs into but I would be unwilling to let that out of my sight and very reluctant to allow someone to probe it. Be aware, the card in that link looks to be for B2500.
You are correct in that the MEN terminal is the K-LiNe in serial port systems.
Of course, I wouldn’t expect you to lend the whole bit of hardware, I was hoping the NGS would be based on some common software like Windows or Linux so the Mazda-specific portions could be employed (and sniffed) on another PC, making it easier to sniff any data. Sniffing data shouldn’t be harmful on either OS but if the NGS has custom software/hardware then it would undoubtedly be a dead end. Otherwise, it might not be possible to activate the PCMCIA card after popping it into a normal PC so there may be no data to sniff going to the car
The most likely approach in that case would probably be something along the lines of the NGS system hooked to the car, with a third wire going from the header in the car (e.g. the MEN terminal) through a little interface circuit to the parallel port on my PC. It’d then just attempt to capture the serial data being transferred, from which I could hopefully figure out a protocol of sorts. Different options on the NGS could trigger different messages, so it’d still be helpful, but more difficult.
Are there any other technical details with the NGS? Anything relating to the hardware protocol/handshaking, or is it mostly ‘this is how to work the NGS’-type stuff? Even just knowing how to say ‘hello’ to the car could be enough to get started
I tried a couple of small experiments, first connecting an oscilliscope to the TEN, MEN and FEN lines on the diagnosis header, but there was no digital signal on any of them. It’s possible some sort of signal is required to tell the computer that equipment is present, but without knowing what the signal is obviously not much can be done about that. In case the ‘I’m here’ signal was the same as OBD2 I actually borrowed an OBD2 reader and temporarily wired it in using the info from the PDF I found, but it couldn’t detect anything, so no luck there.
One unlikely notion I had wsa to find an emulator for the relevant CPU online and try to set it up to run the mark 1’s ROM (faking timing signals/etc.) and see if any likely areas could be identified.
My original post erroneously said all the holes in the header were populated but I was mis-remembering, it’s only a few (e.g. the ones I’ve tried to experiment with 
) But yes, the DIAGNOSIS port under the bonnet at the left is the one I’ve been experimenting with. There’s info that it can support both the “blinky LED” diagnostics (which I’m not interested in) and more informative data streams (which I’ve Googled extensively, found references to but no real info).
Either way, if it’s the case then my hope is restored 
I don’t think I’d bother making an OBD2 adapter though, just go straight to a serial or USB interface. My eventual goal is for an integrated carputer so I can control that side of the software too 
