cant read thru OBD in truck

I recently bought a 2002 Chevy Silverado Z71 4wh and I can not read thru the OBD port with anything I have including Modus Edge, LS Droid or anything! I have a bench harness setup and I can read the PCM that way but not installed in truck. Ive checked all the fuses and been checking the wiring as I found some wires bypassed at the PCM which seem to be CKP, Knock and something else i dont remember now so I reconnected to see what happens and no apparent changes. I have some dash lights on such as ABS and Airbags so I need to be able to read to clear etc not to mention for state inspections

The information below was provided to me by TunerCats:thumbsup:

dave w

Sometimes with these earlier PCMs the OnStar system would cause problems on the communications bus.

To disable the OnStar system in 1999 - 2002 vehicles remove the following fuses:

SEO1 (Special Equipment Options/OnStar)

To disable the OnStar system in 2003 - 2005 vehicles remove the following fuses:

INFO (Vehicle Communications Interface Module)

RADIO (Entertainment System)

If you still have problems reading the PCM try removing the following additional fuses:

TBC BATT (Body Control Module - under hood fuse box)

TGC IGN 1 (Body Control Module - under hood fuse box)

SEO ACCY (Special Equipment Options/Assy)

TBC 2A (Body Control Module)

TBC 2B (Body Control Module)

TBC 2C (Body Control Module)

TBC ACCY (Body Control Module)

IPC/DIC fuse

Also you will occasionally run across after-market devices that are connected to the bus and do not behave properly and these have to be disconnected in order to be able to program the PCM.

There's definitely no OnStar on this truck but there has been aftermarket parts installed. At first glance I know the cats are gone, banks Cai, and headers w/EGR delete. That's as far as I've had time to see. I will however keep digging in and read what you wrote when I get home today and see if any helps or sends me down the right path because it runs and drives which tells me everything is connected etc but the tune is way different than the one in my 01 but since I'm just learning tuning I can't just start changing stuff without knowing why or what it affects. If like to find the OEM stock tune and start over with what I know and see what happens. I have a couple spare PCMs to play with so i don't have to worry too much

TunerCats will sell the most recent .cal file, based on the VIN ($40). Likely your not using TunerCats OBD2, so a "mule" PCM will need to flashed with the most recent .cal file and then read back as .bin file or the file format your using.

dave w

Thanks! I have TunerPro RT if that helps and I have extra pcm if thats what you mean by mule? Sorry Im new to this world and I cant say I get much help either however I will keep trying lol. I cloned my 01 and threw in it and it made it slower and quieter but still cant read any pcm once installed in the 02 truck. I can do anything out of the truck so I cant help but think something else is either bad or wiring issues. I have another obd port but I get voltage etc to the current one. Would a bad bcm cause it or I guess it wouldnt run if thats the case? Im about ready to just drive it and after our new house and shop are done yank it and start over with what I know works and something bigger and better lol of course with kids I still wont get more than an hour at midnight alone to mess with it

Four wires are required for the OBD2 connector, Battery (pin 16), Serial Data (pin 2), and Ground (pins 4 & 5). One option would be to make a temporary OBD2 connector, by reusing Ground and Battery wires and run a new Serial Data wire from the PCM directly to the temporary OBD2 connector. It the Temporary OBD2 connector works, then there is the option to make the temporary OBD2 connector PERMANENT?

dave w

Easy for you to say �� I'll try that and see what happens.

I run a wire from obd to PCM and was able to read in truck but I still can't read abs or airbag info at all and those lights are on. I guess a wire a night and eventually I'll get it finished lol. I did find an OnStar module plugged in behind dash but nothing else OnStar related but removing fuse for that did not help.