OBD gremlins ... need assistance please

[HSRACER]

Originally Posted by BR3W CITY

Pin 4 is chassis ground, 5 is "signal ground"
It may not be the problem, but GM does differentiate them.

The codes you posted would mostly be set to not report, so they exist on the log but don't trigger the MIL.

The "U" code is the one we're having the issues with. Thats the one actually indicating the failure on the OBD circuit. If your actually getting low voltage on the data port it means you have wires crossed somewhere. Put a meter on the data line and see if it reads anything less than 2.5v, as that's what should trigger the DTC.

Will do that tomorrow as well as relocation of the cab ground straps

[Wgesnerjr]

Originally Posted by HSRACER

I am trying to find a pin out diagram of my computer. It is the blue and greeen connector version.

Do you have any idea which color wire is the ground and which is a triggered ground? I would guess the solid one is ground and the white and black one is triggered.

There is a pin out on LT1Swap site.

http://lt1swap.com/2004vortec_pcm.htm

It shows some black/white striped wires as PCM grounds. This might be pin 5 on the OBD connector. I think this is how I wired mine.

The pin out also shows two different Class 2 Serial data wires on the Blue PCM plug. Pin 58 and 59. Could these have gotten mixed up?

[HSRACER]

Originally Posted by Wgesnerjr

There is a pin out on LT1Swap site.

http://lt1swap.com/2004vortec_pcm.htm

It shows some black/white striped wires as PCM grounds. This might be pin 5 on the OBD connector. I think this is how I wired mine.

The pin out also shows two different Class 2 Serial data wires on the Blue PCM plug. Pin 58 and 59. Could these have gotten mixed up?

Pin 58 (the dark green one) is the one running to the obd port and I have verified continuity from pin to pin.

[HSRACER]

What is the best way to get the plastic harness covers off of the back of the computer terminal plugs so I can see the PIN numbers with out breaking them?

[Wgesnerjr]

Make sure the pin at the PCM does not push out of the terminal plug when installing into the PCM. I have had that happen before.

Here is a video that shows how to remove the covers.

https://www.youtube.com/watch?v=yJWzcWiRNVg

[HSRACER]

Originally Posted by Wgesnerjr

Make sure the pin at the PCM does not push out of the terminal plug when installing into the PCM. I have had that happen before.

Here is a video that shows how to remove the covers.

https://www.youtube.com/watch?v=yJWzcWiRNVg

Thank you

[87chevy.com]

Wow, lots of un necessary stuff to remove on the connector from that video...

[HSRACER]

Originally Posted by 87chevy.com

Wow, lots of un necessary stuff to remove on the connector from that video...

What time Saturday do you want to get started? We can do it at my house or Aaron’s place. My garage is cleaner and better lit.

Let me know

[87chevy.com]

PM sent

[HSRACER]

So today’s results were a mixed bag. We did all the things we knew to do and had zero results with this silly obd connection.

The main reasons I needed the obd was to turn the fans control on for my new electric fans and that was when I figured out I could no longer communicate with it.

A couple of days ago I got the computer out of the truck and took it to my tuner. We set the fans at the on/off temperatures we wanted and verified that there were no communication problems with his bench connection.

The fans now work as they should when the truck gets up to temperature and that is the positive part of the mixed bag of results.

The negative is we still can’t get the obd to communicate with the darn computer.

We put all new pins in the Obd and ran new dedicated wires with no splices in them at all. The obd constant power was directly hooked to the battery, the grounds were directly attached to the block, the data line was separate from the harness as were the other three.

Basically we moved the connections outside of the harness, ran all new wires, verified grounds and power with no luck on the communication at all.

This computer will communicate when it is in other vehicles and I am out of ideas!

Anyone have anything else to try??.........
As the post title says.... any help is appreciated

[BR3W CITY]

I noticed you still said both grounds are going to the block. Did you ever look any more at the "signal ground" instead of putting both straight to block? It looks like you tried everything else.

[ls1nova71]

Originally Posted by HSRACER

.
We put all new pins in the Obd and ran new dedicated wires with no splices in them at all. The obd constant power was directly hooked to the battery, the grounds were directly attached to the block, the data line was separate from the harness as were the other three.

So you put new pins in the OBD connector AND the PCM connectors? But it still wont communicate? The grounds are just grounds, I don't think there is any difference in them, so if your scan tool/OBD reader is powering up, then its not a power or ground issue. Are you POSITIVE that the serial data wire is in the correct pin in the PCM connector and the OBD connector? You never know what other people may have messed up. The data wire in the OBD connector should be in pin 2 and the PCM connector pin 58 on the blue connector

[87chevy.com]

Yep, positive the obd wiring is spot on. It has to be a wire shifting to something else causing the obd issue. Down side is no way of knowing since there is no way of knowing unless the harness is unwrapped and all the wires spread apart and trying to read again.. that's my last guess .. it's one downside on Ls swaps the wiring is old, then the junk yard fiddles with the wiring, then an installer mods the harness
. All that wiggling around can lead to wiring issues. The fan wire they left us was 1-2 feet away from the pcm... that wire had had an open causing the fans not to work

[Wgesnerjr]

ok, i'm going out on a limb here but might be worth trying.

Ask the tuner HOW his OBD connector on this bench set is wired in. Where does HE pull power from and where does it go to on the PCM & OBD connector? Where does HE pull grounds from and send to? In other words, duplicate the last known correct functioning while in the truck.

If this can NOT be duplicated while installed in the truck, my thinking here is that maybe, just maybe, there is another circuit somewhere in the harness that is PREVENTING the PCM from communicating. Like one PINK wire that was omitted in the harness and that one slot on the PCM plugs may enable communication. Maybe one Ground on the Bench set up that was omitted and PREVENTS communication? Again, I'm going out on the limb but it sounds like you have narrowed it down to a bad harness.

Look for anything that is not present in the harness but IS in the bench set up. (power, ground, communication wise) If anything, it may shed some light on an issue.

Another thing to consider is the addition of the A/C and other items right before this issue started. Maybe disconnect them to see if there was any affect with communications.

If all this fails...its time to cut the harness open and do it the old fashioned way, one wire at a time. Start with LT1Swap wiring guide and go wire by wire.

[HSRACER]

Originally Posted by BR3W CITY

I noticed you still said both grounds are going to the block. Did you ever look any more at the "signal ground" instead of putting both straight to block? It looks like you tried everything else.

When my friend pulled the obd 2 into the cab of the truck he moved the check engine light into the Dakota Digital gauges also. It was wired and attached to the obd with a small led light.

There was two (and still is a small pink and a small black) wires that were cut and I assume they were for the check engine light.

The check engine light works in the Dakota Digital gauges as it comes on when the key is on and goes off when the engine is running.

I keep wondering if these have anything to do with the situation but am unsure what to try with them.

[HSRACER]

Originally Posted by Wgesnerjr

ok, i'm going out on a limb here but might be worth trying.

Ask the tuner HOW his OBD connector on this bench set is wired in. Where does HE pull power from and where does it go to on the PCM & OBD connector? Where does HE pull grounds from and send to? In other words, duplicate the last known correct functioning while in the truck.

If this can NOT be duplicated while installed in the truck, my thinking here is that maybe, just maybe, there is another circuit somewhere in the harness that is PREVENTING the PCM from communicating. Like one PINK wire that was omitted in the harness and that one slot on the PCM plugs may enable communication. Maybe one Ground on the Bench set up that was omitted and PREVENTS communication? Again, I'm going out on the limb but it sounds like you have narrowed it down to a bad harness.

Look for anything that is not present in the harness but IS in the bench set up. (power, ground, communication wise) If anything, it may shed some light on an issue.

Another thing to consider is the addition of the A/C and other items right before this issue started. Maybe disconnect them to see if there was any affect with communications.

If all this fails...its time to cut the harness open and do it the old fashioned way, one wire at a time. Start with LT1Swap wiring guide and go wire by wire.

It is funny you mention a small pink wire in your post. As I mentioned in my last post there is a small pink and a solid black wire that were cut to move the check engine light to the Dakota dash.

I can try and see where these wires go the next time I have the computer unhooked and see if I can get a pin location.

My other friend who helped me Saturday that moved all the new wiring and installed the pins said basically to start pulling the harness apart as well.

When we tried the fans they didn’t work initially, and we found the fan control wire from the computer open. After running a dedicated new wire from the computer they worked flawlessly.

So now everything is working on the truck...... gauges, fan control, speedometer, great tune, transmission shift points etc.

I am mentally exhausted on the obd issue and just want to enjoy the truck but I know in the back of my mind that it isn’t right.

If I ever have any problems on the road I will be stranded as we wil not be able to diagnose anything until I can get the truck home and remove the computer and get it to my buddy for a bench tune analysis.

This truck has turned into my daily driver as I enjoy it so much. I have others to use but keep going back to this one.

I am working in Chicago this week and will take a break from all this fun and may attack it upon my return or drive it a month or so and regroup mentally.

Btw, I drove it to the airport and it will be the first thing I drive to get home��

[BR3W CITY]

Originally Posted by HSRACER

There was two (and still is a small pink and a small black) wires that were cut and I assume they were for the check engine light.

Are you saying they were cut at the main harness, or cut at the obd plug?

I don't see any black wires going to MIL control on the schematic that I'm referencing (the schematic on Lt1swap, not the harness legend).

[HSRACER]

Originally Posted by BR3W CITY

Are you saying they were cut at the main harness, or cut at the obd plug?

I don't see any black wires going to MIL control on the schematic that I'm referencing (the schematic on Lt1swap, not the harness legend).

I wasn't there the day my friend cut and moved the MIL indicator but it was mounted right on the actual OBD bracket that was left hanging in the engine compartment and was wrapped in the main harness.

He remembers cutting them and moving the new connections to inside the truck.

[ls1nova71]

Originally Posted by HSRACER

We put all new pins in the Obd and ran new dedicated wires with no splices in them at all. The obd constant power was directly hooked to the battery, the grounds were directly attached to the block, the data line was separate from the harness as were the other three.

Basically we moved the connections outside of the harness, ran all new wires, verified grounds and power with no luck on the communication at all.

Originally Posted by 87chevy.com

Yep, positive the obd wiring is spot on. It has to be a wire shifting to something else causing the obd issue. Down side is no way of knowing since there is no way of knowing unless the harness is unwrapped and all the wires spread apart and trying to read again.. that's my last guess .. it's one downside on Ls swaps the wiring is old, then the junk yard fiddles with the wiring, then an installer mods the harness
. All that wiggling around can lead to wiring issues. The fan wire they left us was 1-2 feet away from the pcm... that wire had had an open causing the fans not to work

OK, I'm confused. I thought you ran all new wires? How can it be a harness issue if the wires to the data connector are not even in the harness?

Originally Posted by HSRACER

It is funny you mention a small pink wire in your post. As I mentioned in my last post there is a small pink and a solid black wire that were cut to move the check engine light to the Dakota dash.

I can try and see where these wires go the next time I have the computer unhooked and see if I can get a pin location.

My other friend who helped me Saturday that moved all the new wiring and installed the pins said basically to start pulling the harness apart as well.

When we tried the fans they didn’t work initially, and we found the fan control wire from the computer open. After running a dedicated new wire from the computer they worked flawlessly.

So now everything is working on the truck...... gauges, fan control, speedometer, great tune, transmission shift points etc.

I am mentally exhausted on the obd issue and just want to enjoy the truck but I know in the back of my mind that it isn’t right.

If I ever have any problems on the road I will be stranded as we wil not be able to diagnose anything until I can get the truck home and remove the computer and get it to my buddy for a bench tune analysis.

This truck has turned into my daily driver as I enjoy it so much. I have others to use but keep going back to this one.

I am working in Chicago this week and will take a break from all this fun and may attack it upon my return or drive it a month or so and regroup mentally.

Btw, I drove it to the airport and it will be the first thing I drive to get home��

The small pink and black wires that were cut to move the check engine light are going to be the ignition power for the light and the ground wire for it that goes to the PCM to control it.

Also, you know taking the computer out to scan it wont work, since when you unhook it, it will loose all its stored codes.

My other question for you is, did you just leave this truck at the airport??? That would make me a nervous wreck!

[HSRACER]

Originally Posted by ls1nova71

OK, I'm confused. I thought you ran all new wires? How can it be a harness issue if the wires to the data connector are not even in the harness?



The small pink and black wires that were cut to move the check engine light are going to be the ignition power for the light and the ground wire for it that goes to the PCM to control it.

Also, you know taking the computer out to scan it wont work, since when you unhook it, it will loose all its stored codes.

My other question for you is, did you just leave this truck at the airport??? That would make me a nervous wreck!

Answers to you questions are as follows.

We ran all new dedicated wires to the obd inside the engine compartment and when that didn’t work I elected not to run them into the cab. The harness is thought to have a possible short or grounding issue causing the obd not to work but that is just speculation since we haven’t gutted the harness.

I didn’t know you loose all the info when removing a computer. Thanks for letting me know. I am just now starting my LS Education!

So the cut pink wire is still just capped in the harness as is the ground. I am not sure where my friend picked up the power and ground for the light in the Dakota Digital gauges. Not sure if it will even set a light if a code shows up.

Heck yes I left it at the airport. Who would want an old patinaed 67 when they can pick anything to steal. Also it is fully insured.

[HSRACER]

Here are a few pictures of the old girl in case anyone is interested. Thanks for everyone’s help so far!