07 LT 5.3L Sudden no start/crank

[J-Herkel]

It's not comms with the BCM, it's just the ignition/key start signal. 12V.
and the yellow wire is the starter relay trigger signal.. The BCM is in the middle.

Here's all I can come up with..

Ignition switch "START" -> 12V to BCM (PINK J1-14) [no power? bad ignition switch]
BCM -> 12V to Starter Motor Relay (YELLOW J4-21) [no power with GOOD ignition switch? maybe bad BCM]

Again, that 8V seems low to me.. It may not solve the problem, but I feel like you're skipping a step if you don't test those wires..
(Considering your lights all light up fine, no codes, jumping starter relay socket works, fuses good, new battery etc.)

Or find someone with a scanner that shows if the key is in the start position. (to rule out the ignition switch)

Thank you. I have a friend coming over tomorrow with an advanced scanner to see if it comes up with anything. I'll keep you updated and highly appreciate your help!

 

[rockola1971]

Thank you. I have a friend coming over tomorrow with an advanced scanner to see if it comes up with anything. I'll keep you updated and highly appreciate your help!

Scanner will be practically useless for this failure other than to see input and output state of BCM and PCM. Need to ohm that ground terminal in the relay socket to chassis ground to see if it is electrically connected and rule out a busted wire.

 

[mikez71]

Umm, I thought he already jumped the relay socket and it cranks?
Means power and ground is good already no?