I am trying to use TunerPro RT to comunicate with the ECM on my 95 GMC Sonoma. I get the error that it won't connect. I am using the 2 transistor interface that I monitor with an oscilloscope and it appears to be working because I see the echo coming back on the RS232 RxD line. I am using 9600 baud .
According to the emissions sticker my truck is OBD2 but after reading many forums I think it is really OBD1.5. According to my maintenance manual pin 2 of my 16 pin DLC is the data line but It has no signal or
voltage coming out and I checked its continuity right up to the ECM output pin(VCM-A style #16193495). However, DLC pin 9 has 5 volts and that is the pin I am trying to communicate with.
The Data Stream Definition file(A309.ds) for my truck on the FTP.diy-efi.org web site says the following:
"07/01/94 - Due to G.M. Management indecision, I am unable release data for the 95' OBD-II truck, and have no idea when or how this data will
be released." Bret Henson
G.M. Data Stream Information Guy
I am trying to use the definition file that I downloaded from your web site that appears to be based on the A217.ds definition that is used on the same year truck as mine.
My question is could my lack of communication the ECM be caused by the "Code Mask" byte being wrong for my truck? The one I am using is $0D. I don't really understand What the Code Mask does and how to figure out what it is supossed to be for my truck.
Does wrong Code Mask cause "no connection" error
Moderators: robertisaar, dex
If it's OBD1.5, there's a chance that TunerPro will have trouble connecting to it. If you found the correct DS file for it, then it's definitely either OBD1 (or OBD1.5 - which is really just OBD1 with an OBD2 connector).
From the information you provided, though, it sounds like you haven't found the correct DS file, and A309.DS is probably the right one.
The shorter answer, though, is yes - if you use the wrong definition, it's much more likely that you won't be able to connect.
M
From the information you provided, though, it sounds like you haven't found the correct DS file, and A309.DS is probably the right one.
The shorter answer, though, is yes - if you use the wrong definition, it's much more likely that you won't be able to connect.
M
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TunerPro Author
1989 Trans Am
TunerPro Author
1989 Trans Am
95 was pretty much a conversion year. some vehicles were OBD1, some were OBD2.
some OBD1 vehicles had the OBD2 ALDL, what some call OBD1.5 but they are still OBD1 & you can flash codes by jumpering the right 2 terminals in the ALDL. with OBD2, you can only get codes with a scanner of some kind.
OBD1 uses a PCM & has TBI injection, OBD2 is CPI injection.
you mentioned you have a VCM, its under the hood & it is OBD2.
my book is also giving conflicting info on the ALDL, in one place it shows pin 2 to be the data line for OBD2, in another place it shows to be pin 9.
it may require a scan tool for the computer to output a signal on pin 2.
some OBD1 vehicles had the OBD2 ALDL, what some call OBD1.5 but they are still OBD1 & you can flash codes by jumpering the right 2 terminals in the ALDL. with OBD2, you can only get codes with a scanner of some kind.
OBD1 uses a PCM & has TBI injection, OBD2 is CPI injection.
you mentioned you have a VCM, its under the hood & it is OBD2.
my book is also giving conflicting info on the ALDL, in one place it shows pin 2 to be the data line for OBD2, in another place it shows to be pin 9.
it may require a scan tool for the computer to output a signal on pin 2.
This is an update from my orginal post in July. I have tried many data streams using a trial and error method based on data streams form other vehicles. I tried the MODE 8(Disable Communications), MODE 7(Command Normal Mode Message), different data words etc.etc.etc. At no time did I ever get an "ALDL connected" message. I did this thinking I might be able to turn on pin 2 of the DLC(OBD2 pin) which I monitored with an oscilloscope the whole time. There wasn't even a peep out of pin 2. I finally went with what my Helms manual said which is "if there is no voltage on pin 2 check for shorts then repalce the ECM."
I bought a remaufacrued ECM, had it flashed, hooked it up and I couldn't believe it. When I plugged in my Innova 3100 OBD2 Code Reader it immediately connected and indicated it was monitoring several different sensors. With the original ECM the Code Reader wouldn't connect or show that it was monitoring any sensors. I turned on the ignition and boom all of the sensors it was monitoring dissapeared never to be seen again and the new ECM was just like the old one. My Code Reader works fine with my 1999 Buick Regal and a friends 2001 Sonoma. My guess is that when the new ECM was flashed it turned on pin 2 until I inadvertently turned it off.
The bottom line is I am at the end of ideas and am offically throwing in the towel on the project. I appreciate all the replies. And oh yes, Thank you very much GM!
I bought a remaufacrued ECM, had it flashed, hooked it up and I couldn't believe it. When I plugged in my Innova 3100 OBD2 Code Reader it immediately connected and indicated it was monitoring several different sensors. With the original ECM the Code Reader wouldn't connect or show that it was monitoring any sensors. I turned on the ignition and boom all of the sensors it was monitoring dissapeared never to be seen again and the new ECM was just like the old one. My Code Reader works fine with my 1999 Buick Regal and a friends 2001 Sonoma. My guess is that when the new ECM was flashed it turned on pin 2 until I inadvertently turned it off.
The bottom line is I am at the end of ideas and am offically throwing in the towel on the project. I appreciate all the replies. And oh yes, Thank you very much GM!