2004 Chevrolet Colorado Injector circuit codes

I have a 2004 Chevrolet Colorado. 5 cylinder. My vehicle not a customers. Last month it started stumbling going down the road and would stall intermittently. Scanned it and it had P0201, P0202, P0203, P0204, P0205 injector circuit codes. Looking at the trouble tree. Seemed pretty straight forward. Swap out the ignition start relay and see if it still does it. And it did. Did some basic checks determined it was probably the PCM Changed it. Ran great for 3 weeks. Made a few pretty long tips in it. No problem. Started doing it again on Thursday. As you know they did not make that truck to work on. The injectors are under the intake. I did have to replace the injector harness about 4 years ago. Maybe longer for a P0203. Cylinder 3. Have not checked the ground for the PCM. Looked like it was under the dash. And showed a good ground at the PCM. And also looked like it would cause many other problems if it was the problem. Any ideas? Short of pulling the intake to get to the injectors and harness.

My first thought is a problem at the underhood fuse block. I've seen overheated/spread terminals more than once on this generation of GM fuse block. I can't recall ever replacing an injector on one of those engines for any reason.

 

A quick test would be to watch voltage at pin A of C101, power feed from the INJ 20A fuse to the injectors. Or tap into circuit #839 somewhere between C101 and the underhood fuse block, if C101 is tough to get to.

If you find low voltage on #839 when the fault sets, go towards the fuse block. If voltage on #839 is good when the fault sets, go towards the injectors.