ECU/PCM not communicating

[3linkedchevy]

Went to go get the truck smogged today, my smog guy plugged the computer into his handheld scan tool just to make sure there were no codes. Well, it turns out, that the computer is not communicating with the scan tool. It has power going to the plug but just won't communicate with it. Did some research while I was at the smog place, certain fuses can be linked with the ECU, so I checked those fuses but they were ok. I traced wires as much as I could and couldn't see anything.....

Anyone else had this problem? Does the ECU possibly need to be reflashed or something?

So ANY help is greatly appreciated! Thanks guys

Oh, and this a '97 with a Vortec 350

 

[low4x4]

i had that problem with a 98 and it had a bent pin in the plug...did you check for power, at the fuse, or at the pin in the plug

 

[3linkedchevy]

We know it is getting power, we took the batteries out of the OBDII scan tool he had, and it still turned the scan tool on. I will check for bent pins when I get home this afternoon. Also going to try and chase some more wires. With all the recent fab work, there is a possibility of something getting nicked/cut.

 

[low4x4]

should be power to the truck side of plug...check your fuses

 

[3linkedchevy]

Yeah, the truck side (plug under dash) has power. It just isn't communicating. I checked the fuses that are supposedly linked with the computer. I didn't get a chance to check all since it was starting to get dark and I was still at the SMOG place. Will start checking everything again this week, and talk to my mechanic neighbor who might have some insight.

 

[mattillac]

"..recent fab work.."

Maybe check Circuit #1807, it runs from the Data Link Connector to the PCM.

Pin 2 at the DLC and pin 11 at the PCM "Black" connector C4.

Continuity(0 ohms)between the two connectors would verify that circuit is good(not open).

Looks like that circuit is also spliced into the electronic brake control unit and the evo steering module.

To be sure the circuit 100%, the electronic brake control and the evo module should probably be disconnect, then test the circuit for a fault to ground or +battery.

All the diagrams I have seen show it as a purple wire.

 

[3linkedchevy]

So, I finished checking all the fuses, under the dash and under the hood and none are blown. And didn't notice and bent pins in the connector. But I have been thinking, is it possible that the ECU/PCM needs to be reflashed? Or would the truck not start at all??? I think in order to fully chase wires under the dash, I am going to have to pull the dash out again. So maybe this weekend.

 

[3linkedchevy]

Tried the swapping of the ECUs and no luck. It worked in my friends brothers truck, put it in mine, and same issue. So I am all sorts of confused. The only thing I could possible think is if for any reason removing the ABS and/or airbags.

 

[3linkedchevy]

Well fixed the problem, found a few cut wires that somehow I missed the first few times. And of course one of them was the wire for ECU/PCM data link. And now it is throwing codes. One step forward, 2-3 steps back. haha