OBD II Connection Problem

[Groyd]

Engine 5.3L from 2004 Sierra

When I plug efilive into my OBDII. It says PCM not detected, ECM not detected etc. I have the purple wire (pin2) from the OBD II going to pin 58 on the PCM (dark grn wire) serial data signal. Both the grounds are good on the OBD as well. And I have 12V on the orange. Is there something simple that I'm missing? Any suggestions? Any way to make sure the PCM is good?

[Shon]

Grounds on everything else good?

[vannatta20]

When I did my swap I had the same issue. You cant ground your ground to the chassis. Needs to ground to a ground in the harness Same white and black wire.. Dont know why but it worked....

[Groyd]

Originally Posted by vannatta20

When I did my swap I had the same issue. You cant ground your ground to the chassis. Needs to ground to a ground in the harness Same white and black wire.. Dont know why but it worked....

Are you saying that the two grounds on the OBD2 need to be grounded in different areas or straight into the fuse box?

I'm off work tomorrow, so I can give it a shot sometime.

Thanks for the idea. I hope it works.

[Groyd]

Originally Posted by vannatta20

When I did my swap I had the same issue. You cant ground your ground to the chassis. Needs to ground to a ground in the harness Same white and black wire.. Dont know why but it worked....

It didn't seem to work. Any more ideas anybody?

The ECM/IGN power supply from the fuse box is showing 11.75V. Does that mean the ground isn't great since its not 12V?

[whitelightning603]

If I can piggy back on this thread, I have the same problem. 2004 5.3 4L60E in 87 Silverado. Scanner connected to OBDII gives "Link error". Continuity to PCM on pin 59, 12 volts to connector, grounds from connector to PCM verified. Scanner works properly on other vehicles. Have I done enough homework to declare the PCM bad? Thanks in advance for you guys help. I wouldn't have tackeled this without all the detailed builds that have been posted.




"If you learn from your mistakes, one day I'm gonna be a genius"

[Groyd]

Originally Posted by whitelightning603

I have the same problem. 2004 5.3 4L60E in 87 Silverado. Scanner connected to OBDII gives "Link error". Continuity to PCM on pin 59,

I think its supposed to be off pin 58, not 100% sure though.

[whitelightning603]

Thanks. I contacted Brendan at LT1swap.com. Pin 58 is for trans range sensor-not really needed. Pin 59 is serial data. I guess we are on our own about determining whether or not these PCMs are bad.

[Groyd]

Originally Posted by whitelightning603

Thanks. I contacted Brendan at LT1swap.com. Pin 58 is for trans range sensor-not really needed. Pin 59 is serial data. I guess we are on our own about determining whether or not these PCMs are bad.

Do you have blue/green connectors or blue/red? I have the blue/red.

My first problem is that I have no experience at wiring anything as complex as this. I've been on lt1swap a lot looking for answers.

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

This shows Pin 58 for the OBD II? I'm just making sure I don't need to go out there are change my wiring for the OBDII.

[whitelightning603]

PM sent

[whitelightning603]

Sorry guys, my info on Blue pins 58 and 59 is backward. Pin 58 is serial data. Pin 59 is trans range sensor and can be removed per Brendan at LT1swap.com.
I stated it backward before.

"If you learn from your mistakes, one day I'm going to be a genius".

[jays68yak]

Does the ECM have power? Both Keyed and Constant? And is grounded?

[whitelightning603]

Here is what I have at OBDII connector: position 2 has continuity to Blue harness position 58, position 3+4 are grounded back to PCM ground in harness, position 16 has 12 volts both when key on or off. Position 2 in OBDII conn reads ground whether key on or off.

"If you learn from your mistakes, one day I'm going to be a genius"

[jays68yak]

On the blue connector,
pin 19 should be key power, while in the run position and while cranking
pin 20 should be battery + all the time, even key off
pin 57 should be battery + all the time, even key off
pin 75 should be key power, while in the run position and while cranking


Basicly my thinking is that maybe you guys cant talk to the computer because the computer is not on.

[whitelightning603]

Blue connector pins 19,75 have key power. Pins 20,57 have constant 12v. By the way, when key turned to run fuel pump runs for 1 to 2 seconds. When turned to start will fire and try to run for the 2 seconds until VATS shuts off pump. I have borrowed a PCM and it tests the same.

[Shon]

Originally Posted by whitelightning603

Blue connector pins 19,75 have key power. Pins 20,57 have constant 12v. By the way, when key turned to run fuel pump runs for 1 to 2 seconds. When turned to start will fire and try to run for the 2 seconds until VATS shuts off pump. I have borrowed a PCM and it tests the same.

if VATS have been removed then that is not the issue, the issue is the wire using to run FP, its not staying constant HOT.

[whitelightning603]

Nothing has been done to remove VATS yet. Bone stock PCM that came with the engine from the salvage yard. Since my scanner won't communicate with the PCM, I was trying to solve this problem before attempting reprogram. Just to clarify, shouldn't the scanner be able to communicate with the PCM before any changes are made? Thanks for the replies.

[Shon]

Originally Posted by whitelightning603

Nothing has been done to remove VATS yet. Bone stock PCM that came with the engine from the salvage yard. Since my scanner won't communicate with the PCM, I was trying to solve this problem before attempting reprogram. Just to clarify, shouldn't the scanner be able to communicate with the PCM before any changes are made? Thanks for the replies.

yes, the comm needs to work. I do benchtop programming so I do not have to worry that the OBDII connector is not functioning until I am ready to actually tune.
Who ever is going to do the tuning can remove VATS and other things first so you can get it to run.

And FYI-I use the infor on LT1swap.com to wire in the OBDII connector, in the several dont, never had an issue.

[Groyd]

Thank you everyone for all the replies and suggestions. It turns out that my stand alone harness wasn't allowing the 12V constant to the PCM pins 57 and 20. So...after getting them hard wired in, efilive worked perfectly. I'm going to wait to start it up until tomorrow so the neighbors don't kill me.

Thanks again!

-Matt

[jays68yak]

Originally Posted by Groyd

Thank you everyone for all the replies and suggestions. It turns out that my stand alone harness wasn't allowing the 12V constant to the PCM pins 57 and 20. So...after getting them hard wired in, efilive worked perfectly. I'm going to wait to start it up until tomorrow so the neighbors don't kill me.

Thanks again!

-Matt