i have a 2005 H2 and also have a Tech2 scanner....the issue i have is i can plug the tech2 into the OBD port and key all the info in and am able to read codes and clear them with no issue...the problem is when i go into any option in the scanner whether it's body control, trans, or engine and try to see live data in any of these options.....it clicks several times and comes back and says loss of communication and gives me no data....fuses are all good...candi module is hooked up to tech2 ....it's a 2005 so pre canbus i think.....scanner works flawlessly in other vehicles so i've ruled out a scanner problem....it's got me confused what to look for next....any help is much appreciated

 

Its not uncommon for an aftermarket radio or other electronic equipment to interfere with communications of the modules.

Neal

 

jhall not saying this is the problem, but the candi module is not needed as there is no CAN-BUS in a 2005 (Class2 Serial Bus) it's only required for 2008/9 models with GMLAN High Speed.

I have experienced the same issues and this is what I found:-

• The TECH2 needs to powered only from the OBD2 DataLink Connector, do not use separate 12V from accessory power sockets.
• Communication issues tend to be cause by poor connections at the either the 16-pin OBD2 connector end or the screw-in 16-Way Connector at the Tech2

The cables that came with my Tech2 were pretty low quality so I make sure not to disturb the connectors whilst running tests.

A while ago I made my own cable which worked 100% reliably, unfortunately I sold it as a favor, now I'm back to square 1.

Summary
Don't use the candi module for now, it only adds to the complexity and problems.
Make sure all the connector pins are clean and tight both ends.
Power the TECH2 from the OBD2 port only.


Hope this helps, and If anyone needs a circuit for a new cable PM me.

 

jhall did you make any progress?

 

oceanbrave ...... thanks for checking back in....i really have not figured out what the problem is....it really does not make any sense ....tech 2 will still not stay connected and give me live data....i also have a VXDIAG NANO that i use on a windows laptop with tech2win....i can hook the h2 up to it and it will give me live data but does cut out and back on....that tells me it's still losing communication but the vxdiag just picks up where left off .....i have checked the grounds on the obd2 port....i have also checked the class2 line and am getting some voltage on it as well.....still got me puzzeled....if you have any ideas i'll follow them up and report back....

 

jhall trying to diagnose this issue logically, here are some questions:-

• Are the problems repeatable (hard)? i.e. if you follow the exact same sequence are the results the same?
  • If they are, the electrical connections are most likely good and so the issue is either with the Tech2 or the H2's serial bus.
  • Are you sure you are using the correct Model Year for your Hummer ? (it's not the year of manufacture) As it happens my Engine Trim parameters are always unavailable and I put this down to a Tech2 software issue.
• If the problems are not repeatable it suggests either a comms fault or an intermittent/corroded contact somewhere. Interestingly the GM manual suggests to avoid disturbing the cables or unit when perfuming diagnostics or programming. Try and isolate the source of the problem:-
  • Keep the Tech2 and cables perfectly still whilst diagnosing, if this improves or changes things carefully check the wiring.
  • Is your battery charged and at the correct voltage (>12.6V) ?
  • Is the Fuse CIG LTR (Under the hood) clean and connected solidly (Tip check the 12V here too, both sides of the fuse)
  • Is there any aftermarket equipment connected to the comms bus?
• If possible try your kit on another Hummer H2 to prove it works.

If your Tech2 is proven to work on another H2 and all the cables and connections are solid, there may be a faulty or badly connected module corrupting the bus. There are (I believe) diagnostic videos on YT which show how to check the Class2 Serial Comms

Splice Packs 205, 206 & 207 are where all the serial bus module connect (Left of Dash) I seem to recall a forum member with a similar problem (try searching SP205 etc) Each module can be isolated at the splice packs.

Personally I think the replica connectors and cables are often of very poor quality, as I mentioned I made my own which were much more reliable.

If still stuck come back for more suggestions.

The Tech2 is old technology, slow and quirky and if you've noticed the date has to be set back to something like 2017 otherwise you get an RTC fail at start-up. However believe it or not the Tech2 is packed full of electronics, quite amazing.

What is frustrating is that as you say, it forgets where it was so a lot of time is spent returning to the place you were at just before you pulled the connector out.

Found this video which may help..

 

funny video. you can see water dripping all over the DDM from a bad door seal at 30 second you see it is wet and at 37 seconds you see drips coming down

 

oceanbrave.....thanks again for the info ....i have already looked into the splice packs....no issues there....the tech2 has no issues at all pinging the modules in the settings ....i can also ping each one at a time and all seem to not be having any issues ....i really think there is a problem with the serial line somewhere...where it momentarily drops out then right back on.....i am going to take a hard look tomorrow at the obd2 port and see if maybe the terminal is loose or if it has any type of corrosion in there ...only aftermarket module i have is an aftermarket radio...it shows no issues when i ping it on the tech 2 but i still took it out of the comb in 205 and no changes.....i'll have a few hours to troubleshoot it some tomorrow....hopefully it'll show it's self tomorrow!!!

 

Must be a really bad seal, even the Tech2 is wet. However it looks like it was raining, so presumably the door was opened to get inside?

Is that why DDM's fail so often- opening the doors in the rain and water pouring down the switches?

 

You are obviously well into it but it does seem like a classic comms issue, as if something is periodically interrupting.

Picked up on a couple of points:-

According the the diagrams pulling SP205 would leave the OBD2 port + Tech2 unconnected (Purple wire -Pin D) so in theory the Tech2 shouldn't work which may have confused things.

Also there are 2 grounds in the ODB2 port, one on Pins 4 (screen) the other Pin 5 (Signal Ground) here is a simplified cable drawing for the Tech2 in case you want to check it's connectivity. Both grounds are important, interestingly they go to separate ground points Pin4 4 =G203 (Right Lick Panel) and Pin 5 = G200 (Left Kick Panel)



This YT video is interesting.


Also are you saying there is an aftermarket radio is connected?
- if so I'd 100% try disconnecting it, actually SP206 should disconnect all the audio stuff (assuming the aftermarket radio picked-off the same feed)
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