2012 GMC Sierra 1500 SLT Crew Cab 4x4 (LC9) ENGINE FLEXIBLE FUEL,(GAS/ALC),8 CYL

UO100 code, Fuel pressure sensor Circuit b, Abs code brake switch circuit invalid data. Service stabilitrak light is on. No check engine light when ignition initiated. No crank no start but all electronics function properly accept for crank and comm with pcm. 
Transmission emitting a constant beep when ignition is on coming from fluid pan area. 
im not able to get my hands on accurate wire diagrams. I have removed the pcm harness and throughly checked it. There were bare wires on the camshaft sensor and the two fuel injectors. Had a bad coolant leak that seaned to get on just about everything. I checked and cleaned grounds that needed. I’m able to get the beep from transmission to stop by removing trans ignition fuse or I can remove run crank relay. Pink and white wire is the ignition power supply I believe but don’t have diagram. I traced it to the tehcm connector I believe. When I unplugged code for loss of communication with tcm showed up. However beep stopped. The wires coming from the cab to fuse box as well as multiple clusters inside the cab were sticky wet when opened. I’ve spent a couple weeks with my limited knowledge so there’s lots more I’ve done. I did check 5 volt reference. All show zero. At pcm a few show .17 volts or something close to that. 
also I removed the connection to the transmission and probed the pink and white connector. When the fuse is installed it showed battery voltage with ground in connector and positive on battery positve. When the fuse  is removed it shows battery voltage but volt meter leads have to be reversed. 

Let's see why the PCM is offline first by checking its Powers (2) and Ground.

I provided a pinout for Connector X1 at the PCM.

Let's check the power and grounds to the PCM using a 4 amp headlight bulb (Best) or at least an incandescent test lamp.  So you are aware an incandescent lamp can lead you down a rabbit hole because it doesn't load the circuit enough to be sure there are no voltage drops.

With a test lamp to ground and check it lights on a known good power source:  pin 20 is B+. Bright light? Y/N
                                                                        pin 19 is Key On Engine OFF supply voltage.  Bright light? Y/N

With the Test lamp to B+ and check the lamp lights on a known good ground:  check Pin 73 for a good ground. Bright Light? Y/N





 

Thank you so much for your reply I apologize I didn’t answer sooner. I actually had that pin out just wasn’t sure it was correct. I did check all three and they showed battery voltage.

 I did check all three and they showed battery voltage.

There should only be battery voltage on PINS 19 and 20.

There should be no battery voltage on the ground Pin 73. It is a ground.  If it was a voltage drop test no more than 300mV.

Did you use a DVOM or a Bulb to test this?

Bad wording my apologies, 19 has battery voltage with key on, 20 has b+ voltage at all times, 73 is a good ground, bright light, check resistance to all engine grounds as well.
19 I probed while light was on b+ got a dim light and sounds like the transfer case actuator kicked on.

19 I probed while light was on b+ got a dim light and sounds like the transfer case actuator kicked on.

If you tested pin 19 with the test lamp connected to battery positive and got a dim lamp, you are finding a ground path when there should not be one.

Disconnect X1 PCM connector;

To be clear, with the test lamp on battery Negative, pin 20 is bright, and with the Key ON pin 19 is bright?

While you are disconnected, with the Key Off, put the test lamp to battery Positive and probe pin 19, Dim Light?

The reason we need to be sure here, is it sounds like your Pin 19 has a power supply issue, if that is the case, we need to determine why as the next step.

If these check good, we go after the information bus next.  Need to get the PCM back online, that will more than likely solve some other issues that are occuring.

At this point these two Diagrams may be very handy;

 
 




 

Yes pin 19 with key off and test light on battery positive. Dim light but with key on and test light on neg the light is bright.
20 was only lit when light was on neg. And the ground on 73 was also good. I checked all of these with the plug disconnected. If need be I can back probe them.

Alright, the reason you heard the transfer case kick on was because you fed that wire power with Battery positive, the lamp limited the current flow,

SO if your ground is good, and Key ON pin 19 Lights a 4 amp bulb with the lamp connected to ground, and 20 lights up as well, your power and grounds are good.

Key ON you have no check engine light on the Dash, correct?

Before we go any further is there only 2 PCM connectors or is there 3? If it's a 3 I gotta check for more power and grounds from service info.

If it is a 2 connector PCM; let's check the Can-Bus integrity at pins 6, 14 at the DLC (Diagnostic Link Connector)
 

Disconnect the Negative Battery Cable, Measure for voltage at pins 6 and 14 from a known good ground, we don't want to see any voltage on these 2 lines.
Switch to the Ohmmeter and measure the resistance between pins 6 and 14, what do you have?

It would also be nice to know if you have a 5 volts reference coming out of the PCM with the key on, using a voltmeter backprobe the wires of the MAP sensor and check for 5 volts.  Disregard this this I read you don't have the reference!!

 





 

 

Correct no check engine light, 2 connection pcm. First thing in the morning I will check 6 and 14 at the dlc with negative battery cable disconnected. And the resistance between the two. I checked the resistance last week it was 61.5 ohms but I will check again to be sure I didn’t make any mistakes. 5 volt reference I checked at multiple sensors and had little to no voltage. I’ve been watching your YouTube videos and reading as much as possible it’s just a lot to learn in little time. I very grateful you are taking the time to help me.

0 volts between the two. 60.3 ohms of resistance

Between 6 and ground and 14 and ground. Resistance from 6to 14 is 60.3

That's good to see 60 ohms between 6 and 14 at the DLC. 

My eyes aren't as good as they used to be lol.  Something didn't seem right with only 2 PCM powers!!!

There is one more to check:
 

In this diagram we see Pins 19(KOEO),20(B+), and 47(KOEO)!!!  

1. Need to check Pin 47(Pink w Black Tracer) lights a 4-amp bulb with PCM Connector X1 Disconnected, Light to battery ground and turn the key ON, do you have a bright bulb?

2. I am also curious to know if the theft light is going out with the key in the RUN position?

3. Do you know what module set the U0100 code?

If the theft lights goes out, that means the PCM is online and communicating with the BCM, which is good.  They verify the Key handshake.

So check this pin 47 for Key on Power,  without a scope we can't see what the CANBUS is doing, but 60 ohms means the Bus is intact.

The MIL (Check Engine Light) is turned on by the PCM to the cluster by proving a ground path at pin 68 of the PCM X1 harness.  You can turn the light on by providing a ground with a test lamp on Pin 68 (plugged in) with the Key ON, to verify the light does actually work.

If the bus is intact, and the PCM 3 powers and 1 ground are good,  I would next want to see why or if the 5v ref is being pulled down. You need to unplug all the 5v ref sensors to see if it returns while monitoring a line with a Voltmeter.

There are 2 main 5v PCM Outputs here is a diagram;   (Don't worry about any temp sensors they are individual 5v circuits)
 

And here is the X2 PCM Pinout you'll need;
 

Sorry I lead you astray on the powers and grounds!!!
 

No power to 47, no light at all. I was able to get the check engine light to illuminate. The antitheft light is functioning as usual. It turns off and I’m able to turn it on and off with the key fob

Ok!! Let's work backwards from the PCM to the FUSE 5 ECM/THROT

WIth a test lamp to battery ground, check the light on a known good power source;

Does both sides of Fuse 5 have power with the key on?

This fuse receives its power from the RUN/CRANK relay.  Fuses 4,5,18,8,24,13 all receive power from this relay.

The relay is groundside switched from the PCM PIN 59

So lets work from the fuse back to the relay, then possibly back to the PCM to see if it is grounding Pin 59

I’m not home at the moment but I know for a fact the mentioned fuses are not receiving power. The run crank relay does click on as soon as the key is turned on. I know this because I was chasing a constant beep at transmission when the key is on. Led me to a pink and white wire that goes from trans ign fuse (19) to the 4 wheel actuator and the tcm round connector on passenger side of trans. It also is connected to pin 19 at pcm. (19) and all ign fuse such as ecm ign, misc ign, hvac ign etc receive power when run crank is energized/ when key is on. I will confirm all the fuses but I checked that already and remember ign fuses receiving power or losing power with run crank relay. I thought fuse 5 and other mentioned got energized by the power train

Looking at the diagram you sent fuse 5 and others mentioned get energized by power train relay.

Just cause the relay clicks, doesn't mean it's good.  Swap it out with another of the same type that is known good, some have diodes and some don't.  Might just be bad contacts in the relay.

Yes sir I’ve tried that and same result. Only things that are being powered when run crank engages are the fuses labeled ignition. Should there be more? I’ve been thinking this whole time the powertrain relay gave fuse 5 ecm/throttle power? The diagram you sent shows pin 47 from ecm (pink with black tracer fed by fuse 5 which is fed by the powertrain relay which is fed by yellow wire pin 59 powertrain relay control and ecm battery. Am I reading that wrong?

It’s been raining all afternoon so I wasn’t able to check the ground on pin 59 but will in the morning

Pin 59 is a switched ground by the PCM to turn on the relay.  It should switch to ground when the Key is On.  This is what gives pin 47 its power.

This is gonna be your next step to prove out the wires at the relay I would think.

That relay puts power to a lot of other fuses.