wiring diagram question?

printed out a wiring diagram from Mitchell on a 2006 5.3 liter 4x4 Tahoe under engine performance and pasted all five pages togather according to wire numbers. Page 1 on one end has a picture of PCM with 80 pins and page 5 on the other end has a picture of a PCM with 80 pins and wires.
what I don't understand is that pin 74 on page 1 at PCM is a ect sig with yellow wire but page 5 at the PCM pin 74 is a lt grn wire/ho2s low control. What don't I understand?















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Good question, nori! The answer is that this PCM has two 80-pin connectors, C1 and C2. I don't have access to Mitchell, but I looked this up on the BBB Industries site to be sure.

Here's the ECT sensor wiring:



Sure enough, pin 74 of C1. Note the CONN ID box in the upper right, identifying the two connectors by color.

Then there's the O2 wiring:



And there's the other pin 74, on C2. It's easy to get confused when the diagrams get this big! :lol:

Hi, Tyler
thanks for the quick response-does that mean that the PCM has 160 pins?

No problem!

nori wrote: does that mean that the PCM has 160 pins?

Total, yep. I dunno if the PCM actually uses all those pins, but they're there.

thanks again TYLER,
YOU'RE A WEALTH of KNOWLEDGE! Didn"t think a PCM would have to that many pins -retired mechanic ( I am definitely getting older).

Thank you Tyler!

nori wrote: thanks again TYLER,
YOU'RE A WEALTH of KNOWLEDGE! Didn"t think a PCM would have to that many pins -retired mechanic ( I am definitely getting older).

My pleasure! We're you chasing a specific issue on the ECT or O2?

I just replaced my oil pressure sending unit on my 2006 Tahoe 5.3 liter by braille! I was just thinking how bad it would be if you had a wiring problem with that circuit and had to back probe it-lucky for me chev still places their oil pressure switches back where the distributors used to be (showing my age ).Printed the complete engine performance wiring diagram for future reference.

Ah yeah, the ones behind the intake! Those are always fun to replace. :lol: I quit trying to probe those, and just go directly to unplugged tests.