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[General] [VT/VX/VY/VZ/VE] Everything to know about OBD2 (ELM327) Diagnostic Cables

TazzI

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The cable I bought has OBD2 capability but not I suspect ALDL . I was asking if a software program might get it working with ALDL too ?
No worries :beer chug:
Unfortunately you cant rig an OBD2 cable (such as an ELM327) to work over ALDL. They are completely different protocols that use completely different chips to "interpret" the incoming signals from the car on different pins of the diagnostic port. As nice as it would be, software cannot help here either as it is the actual hardware that is the issue.

So what I'm reading is this will work with apps on android on a VX LS1? Looks like a good piece of kit - I stupidly bought one of those generic $20 things on ebay which of course didn't work (I know, I know) was hoping someone would release a good one.

Also big props to the OP, great writeup.
Stupid bluetooth units are temperamental, seems the smaller they are.. the more dodgy there connection is! I highly recommend everyone to use a legit Scantool.net cable as they are very high quality units, there bluetooth units actually work perfectly at high speeds too which is a big help. Torque app works brilliant, just recently used it on my android nexus 7, you can even upload custom themes/gauges made by others which look really mint!
 

EHVS

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OK, so I bought a mini bluetooth elm327 on feebay. I know, I know I should have listened etc. but there were enough good luck stories around to persuade me to take a punt on one of these cheapies.

Well, I have a problem. It doesn't work on my '07 VZ v6. I thought the unit may be faulty, but it turns out it isn't.

I tried it with Torque, Car doctor, scanmaster and a couple of other apps on two different android units. The adaptor is found and paired easily on either of the droids. When an app is launched and asked to connect, it does and then starts an auto process of testing all the obd2 protocols but ends up saying things like "Cannot connect to ECU" etc. The torque app is different, it just keeps asking for the pairing code and then fails.

The unit works perfectly on a 2003 Holden Astra using any of the apps. Why? The dumbay seller says the commo is not obd2 compliant, I tried to explain otherwise, but whatever.

Why does the unit work flawlessly on the Astra but not the VZ?

I understand that most of the systems are still ALDL in the VZ but not the ECU. Anyone have a clue?
 
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that's a strange one mine works on my ve with torque and other programs also
have you had your ecu remapped and locked?
 

EHVS

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that's a strange one mine works on my ve with torque and other programs also
have you had your ecu remapped and locked?

nah, it's completely stock.
 

TazzI

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OK, so I bought a mini bluetooth elm327 on feebay. I know, I know I should have listened etc. but there were enough good luck stories around to persuade me to take a punt on one of these cheapies.

Well, I have a problem. It doesn't work on my '07 VZ v6. I thought the unit may be faulty, but it turns out it isn't.

I tried it with Torque, Car doctor, scanmaster and a couple of other apps on two different android units. The adaptor is found and paired easily on either of the droids. When an app is launched and asked to connect, it does and then starts an auto process of testing all the obd2 protocols but ends up saying things like "Cannot connect to ECU" etc. The torque app is different, it just keeps asking for the pairing code and then fails.

The unit works perfectly on a 2003 Holden Astra using any of the apps. Why? The dumbay seller says the commo is not obd2 compliant, I tried to explain otherwise, but whatever.

Why does the unit work flawlessly on the Astra but not the VZ?

I understand that most of the systems are still ALDL in the VZ but not the ECU. Anyone have a clue?
*sigh*.. yes I cant help but say it. But I told you so!.
Alot of softwares are starting to "prevent" these cheap cables fro working. This includes scanmaster, easyobd2 ect. These places are making deals with scantool providers like Scantool.net so that they can both profit significantly instead of the little asian sales man.

In saying that, your VZ commodore will speak over CAN protocol and ALDL. But as you said, all systems speak over ALDL except for the PCM (ecu). These cheap elm devices are smart.. but not 100% perfect. They can *auto detect* the protocol most of the time, but sometimes they fail or choose the wrong one. By the sounds of it, the apps are trying to use the *auto detect* feature and they are getting nothing back. If you can, try manually select a can protocol (11bit or 29bit) and see how you go.

Also, good old GM made the CAN communication a little unordinary.. The ELM devices will throw a "DATA ERROR" fault as the CAN frames are structured differently thus alot of softwares fail when seeing the error. This error can be switched off with the correct commands to the elm.. although generally only smart developers implement this.

I know the above from personally developing my own obd2 software for monitoring the bus, and a few that tried it with CAN protocol came up with that error until I made appropriate changes! If I had enough support/testers, I could get a CAN compliant app for the VZ's off the ground alot faster!

Hope that sort of helped! Your best bet is to just try a whole bunch of "trial" paid software and see which one works for you before full purchase. I also recommend getting a USB version :beer chug:
(Oh, sorry for the late reply!)
 

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Thanks Tazzi, all your efforts are much appreciated. The seller is sending a new identical unit for me to try. This might prove something or at least give me a chance to.

" If you can, try manually select a can protocol (11bit or 29bit) and see how you go." - Oh god how many times and variations I tried already.

I've just been looking over some datasheets on the el327p IC (genuine Elm Devices) and example application.
The chip deals with all the obd protocols via 3 physical and isolated busses:
1. SAE J1850
2. ISO 9141-2, ISO 14230-4
3. ISO 15765-4, SAE J1939
There seems to be a potential here that the CAN problems on these bluetooth devices stems from incomplete implementation on the 3rd bus. The other busses allow for simple discrete transceivers, but the CAN uses an MCP2551 etc type chip for the interface between obd port and elm327 chip. Another possible failure point. I have come across the GM single wire issue while researching. Do you know if that is the case with commodores? This would make the design around the CAN High and Low lines an issue that needs addressing.

I found (online at least) the Astra which works well with the mini327, uses KWP (under ISO14230-4) so it uses a different hardware path within the mini327 device (up until the output i/o BT,USB etc) than what the commodore uses.

Thanks again for your wonderful info.

Just to be clear, the OBD2 protocols used in commodores are: VPW, CAN 11bit High, CAN 11 bit Low, CAN 29bit High, CAN 29bit Low.
*Note, CAN high and CAN low are the same protocol.. just one speaks much quicker than the other!

Just a note, I don't think that's what CAN high and low means. They are not high and low speed, they are a differential signal pair (higher volts and lower volts) in order to eliminate interference at high data speeds. Could you please tell me where you found the info on what protocols commo's use? If they are single wire, for example CAN 11 High, that same system would probably not function by switching the OBD device to CAN 11 Low, although there is a slim chance you could get really lucky.

If I knew the exact protocol of the VZ I could try a mod that may get this bluetooth thing to work.

Will try and report any info I work out.
 

TazzI

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Thanks Tazzi, all your efforts are much appreciated. The seller is sending a new identical unit for me to try. This might prove something or at least give me a chance to.

" If you can, try manually select a can protocol (11bit or 29bit) and see how you go." - Oh god how many times and variations I tried already.

I've just been looking over some datasheets on the el327p IC (genuine Elm Devices) and example application.
The chip deals with all the obd protocols via 3 physical and isolated busses:
1. SAE J1850
2. ISO 9141-2, ISO 14230-4
3. ISO 15765-4, SAE J1939
There seems to be a potential here that the CAN problems on these bluetooth devices stems from incomplete implementation on the 3rd bus. The other busses allow for simple discrete transceivers, but the CAN uses an MCP2551 etc type chip for the interface between obd port and elm327 chip. Another possible failure point. I have come across the GM single wire issue while researching. Do you know if that is the case with commodores? This would make the design around the CAN High and Low lines an issue that needs addressing.

I found (online at least) the Astra which works well with the mini327, uses KWP (under ISO14230-4) so it uses a different hardware path within the mini327 device (up until the output i/o BT,USB etc) than what the commodore uses.

Thanks again for your wonderful info.



Just a note, I don't think that's what CAN high and low means. They are not high and low speed, they are a differential signal pair (higher volts and lower volts) in order to eliminate interference at high data speeds. Could you please tell me where you found the info on what protocols commo's use? If they are single wire, for example CAN 11 High, that same system would probably not function by switching the OBD device to CAN 11 Low, although there is a slim chance you could get really lucky.

If I knew the exact protocol of the VZ I could try a mod that may get this bluetooth thing to work.

Will try and report any info I work out.

Yeah there is high and low can. 250kb/s and 500kb/s. And on both 11bit and 29bit streams. Its a little confusing at first, but its how GM allows for large generic information to be transmitted quickly (29bit) and more specific,programming ect information to be performed (11bit). VZ's dont use single wire gmlan communication, thats only VE+. VZ will be using CAN 29bit and 11bit. If you read through the ELM327 documentation sheets, you will see exactly what protocols are supported on the ELM. The ones I was looking at can be seen below, these are actually documented in the elm datasheets:
obd2soft.png

I wouldnt have thought the CAN transceivers would be the issue. Only the actual elm device keeping up with the comms. As even at 115200 baud. the buffer still gets full immediately. I'll go through my development thread and let you know exactly which protocols the boys were using to test out the software comms. Should send you into the right direction.
*Edit, just had a quick look. I think the VZ's were 11bit 500k/250k.
If the elms werent setup correctly, messages like this would appear:
43 41 4E 20 45 52 52 4F 52 0D 0D 3E CAN ERROR..>

Including that CAN ERROR, which normally sets the software way off as its not expecting it! It means "Invalid format" which can actually be turned off like I said previously. Not sure whether its your ELM device, or simply the software your using unless we actually see if the bluetooth device is actually seeing any data on the CAN line.
 

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Well, 2nd device arrived and it's the same story. No go in the VZ. Works on Astra, confirmed to be KWP(fast) protocol.

Forgive me for the nerd detail, but someone may find it useful.
I opened one up to see what's going on.
It's not based on a genuine elm327 chip, but a PIC18f25k80 (http://ww1.microchip.com/downloads/en/DeviceDoc/39977f.pdf) which seems to be implementes the same way.
It uses a TJA1040 CAN transceiver (http://www.nxp.com/documents/data_sheet/TJA1040.pdf)
The TJA1040 is setup with 120ohm resistor (surfacemount labeled 121 in position R2 on my device) which provides loading across the CAN high and low lines (hardware not speed**). The datasheet shows typical applications with two resistors using a split load for 'stability'.

Following some crazy idea, I removed the 120ohm resistor, with no change to the function of the device. It doesn't come into play unless CAN protocol is used. It didn't help.
This device was a fun little research tool, but useless for the VZ. I tried a few different Android BT terminal apps in an attempt just to see the raw data/signal, which just disappointed me with the crap that's out there.
The device itself is most unpleasant to work on, with 2 stacked double sided pc boards whose headers are soldered to each other.

Not that it helps anyone with a commodore but I would be happy using this mini bluetooth device with protocols other than CAN.

My next option will be a usb cable job. Hopefully that will be less drama, even if it's less convenient. If anyone has had success with the chinese ebay ones on a VZ, please chime in and let us know.

**To clarify the 'high' and 'low' terminology (I'm agreeing with you Tazzi) - There are slow and fast speeds, there are High and Low CAN lines. Instead of a single wire for serial data they use a balanced pair regardless of the baud rate. The extra confusion comes from GM also using 'single wire' CAN. They could use CAN High or the CAN Low wire. Bloody hell, my own clarification reads badly.
 
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