intermittent electrical issue no crank no start

tyler1983

New member
Aug 8, 2016
7
0
0
georgia
hello everyone im new to this forum but not new to the diesel world. i am a diesel mechanic mostly heavy duty. i have 05 duramax 2500hd LLY, the drivetrain is completely stock, no programmer, no cold air intake and no exhaust. i put six inch lift and 35in tires on it a little over a year ago. i have had the truck for almost five years now. the truck has give me little to no problems other then some seals leaking and fuel line leak. the truck has 225k mile on it. about a week and a half ago i was working and needed to move my truck and when i started it and put it in reverse it shifted really hard and would not move and the message center on the dash said service 4wd. i shifted the trans to drive and back to reverse and the truck moved just fine. later that day it started raining so i got in the truck to get out of the rain and i started the truck to turn on the ac and after only a few mins of running the ac quit working, so turned the truck off and then tried to restarted truck and it wont do anything not even click the starter. the check engine came on and so did the abs and brake lights along with the message saying service 4wd. i checked all the fuses,the batteries and anything i could think of. i hooked up a scan tool it said that there was no communication with the TCM and ABS modules. never could get the truck started that day. next day i went to go load the truck on a trailer and it started up just fine but all the lights where still on on the dash so i decide to drive it home and it was in limp mode and would no shift out of second gear. got it all the way and shut it off and it would start right back up and slowly but surely everything in the truck started working again. drove the truck for a week til this morning and it would not start and all the lights where back on on the dash. the only common occurrence between the two times is rain, it poured down yesterday but i did drive the truck yesterday just found out it wouldnt start this morning.

thanks for any advise before hand and could use some help on this one cause i have got to be overlooking something.
 

BLACKMAX1

WAY2EVL
Jul 10, 2013
538
0
16
VA beach
How old are the batteries and are the terminals tight, even where the cables connect to the terminals? Also check the bail connectors on top the motor and the wire harness on the driver side, sometimes the harness rubs against the fender and liner and causes weird electrical issues.
 

tyler1983

New member
Aug 8, 2016
7
0
0
georgia
the batteries are bout a year old had them both tested and checked out good. checked all the battery terminals and all are good and tight. i will check the connectors and harness when i get back to the truck in a little while

thanks
 

tyler1983

New member
Aug 8, 2016
7
0
0
georgia
i checked all the connectors and harnesses on the driver side. i removed the fender well cause i found a spot that was rubbing on the harness after further inspection it had only rubbed a hole in the wire loom and had not damaged any of the wires. would anyone have any wiring schematics to help me out on chasing wires.
 

tyler1983

New member
Aug 8, 2016
7
0
0
georgia
here is a list of the current codes in the truck,

ECM U0101 lost communication with transmission.

TCM will not communicate

BCM B1440 power mode master input circuits
U1000 loss of serial communication for

cluster U1000 loss of serial communication for

HVAC B3770 airflow control 6 feedback circuit
B0414 temperature control 1 feedback circuit
B0424 temperature control 2 feedback circuit
B1375 device ignition 3 circuit malfunction
 
Last edited:

DAVe3283

Heavy & Slow
Sep 3, 2009
3,407
31
48
Boise, ID, USA
It sounds like you have a major power or ground problem affecting several modules.

The TCM grounds can be burned out if the truck is jump started and one of the jumper cables touches the TCM case. To test if that is the case, connect a jumper wire from the TCM case to the battery ground. If the TCM comes back to life, then the ground is damaged, either internally to the TCM or in the harness.

The various BCM & HVAC codes could be caused by a poor ground. I am drawing a complete blank where the ground for the body is. I want to say it was near the ABS module?

Here is some info from GMUpfitter that might help: https://www.gmupfitter.com/publicat/2004_BB/2003_Beyond_LD_Electric_CK.pdf
 

tyler1983

New member
Aug 8, 2016
7
0
0
georgia
i have tried grounding out the case on the TCM and that didn't change nothing. checked the power and the ground in the harness and even checked the resistance of the wires. checked the data bus for resistance .3 to .5 ohms on all wires checked. checked for power on the ignition 3 circuit and only get half a volt not sure what i should get there but thats what im getting. not sure where that circuit goes and controls haven't been able to locate it in all the schematics that were sent to me. and if anyone knows exactly abs module is i would greatly appreciate it.
 

tyler1983

New member
Aug 8, 2016
7
0
0
georgia
Update

okay after three days of pull my hair out i stumbled on to what i guess is the problem. i was back probing the TCM checking grounds and powers they were good. but while i back probing pin #3 on connector c1(grey) orange power wire the needle had slid over and also made contact with pin #4 pinks and and the lights in the dash went off and the truck would crank but i didn't start the truck since i have so much of the truck apart. i will put the truck back together and confirm that it does start. now if the probe is removed the truck goes the truck goes back to no crank with all the light on on the dash. so does this mean the tcm is fried and does anyone know how much voltage should be on the pink wire in pin #4 also while the pins are jumped together the battery light on the dash even with the switch off and keys out of the ignition.
 

redneckcwboy

New member
Aug 16, 2010
2
0
0
Az
No start follow up

I have been having The same problem going on and have been pulling my hair out every since. It started out about two years ago with a dead battery, I replaced them and it cleared up for a while. I removed the aftermarket alarm think that was a possibility, but not (still left it out and switched to factory key fobs). I've checked everything as well (connections, voltage, ohms, continuity, no chafing). I ended up making a bypass switch putting power to the primary accessory wire and using a push button to start as the factory ignition switch will not key start.

Some symptoms along the way:
No gear selector indicator (GSI)
Key will not start, no power transfer through the ignition switch
Ignition switch not powering on half of switch
Blower motor does not work
Transmission Control Module (TCM) loss of communications

Items replaced:
New batteries
New Body Control Module (BCM) married to the truck by dealer
New Nuetral Saftey Back Up Switch (NSBU)
New Ignition switch

Some temporary solutions along the way have been;
Ice picked electrical connections and applied dielectric grease
Wiggle bcm connections and temporarily got gear indicator back
(Bypass switch 1 - red 12v+ to primary accessory orange wire: turns on blower motor, GSI, and TCM comms; - switch 2 DPDT, On = normal operations key start - Off - On = power to switch 3; switch 3 = push to start button)

It would sometimes start with only switch 1 On and key to start, worked this way for quite a while. Then one day at random I had to sequence the switches to start. Then went back normal operations key only. Then back to switch 1. Now back to switch sequence.

Summary:
Tcm ground is ok.
No gear selector indicator
No key to start
Still a loss of primary accessory wire (orange) power through ignition switch, I think this is the problem right here. I been trying to get a diagram to see what the ignition switch activates along the way to key up power to the accessory wire/second half of the ignition switch.
 
Last edited:

BradMike

04.5 LLY XCLB
Feb 5, 2020
2
0
0
Bc, Canada
I have been having The same problem going on and have been pulling my hair out every since. It started out about two years ago with a dead battery, I replaced them and it cleared up for a while. I removed the aftermarket alarm think that was a possibility, but not (still left it out and switched to factory key fobs). I've checked everything as well (connections, voltage, ohms, continuity, no chafing). I ended up making a bypass switch putting power to the primary accessory wire and using a push button to start as the factory ignition switch will not key start.

Some symptoms along the way:
No gear selector indicator (GSI)
Key will not start, no power transfer through the ignition switch
Ignition switch not powering on half of switch
Blower motor does not work
Transmission Control Module (TCM) loss of communications

Items replaced:
New batteries
New Body Control Module (BCM) married to the truck by dealer
New Nuetral Saftey Back Up Switch (NSBU)
New Ignition switch

Some temporary solutions along the way have been;
Ice picked electrical connections and applied dielectric grease
Wiggle bcm connections and temporarily got gear indicator back
(Bypass switch 1 - red 12v+ to primary accessory orange wire: turns on blower motor, GSI, and TCM comms; - switch 2 DPDT, On = normal operations key start - Off - On = power to switch 3; switch 3 = push to start button)

It would sometimes start with only switch 1 On and key to start, worked this way for quite a while. Then one day at random I had to sequence the switches to start. Then went back normal operations key only. Then back to switch 1. Now back to switch sequence.

Summary:
Tcm ground is ok.
No gear selector indicator
No key to start
Still a loss of primary accessory wire (orange) power through ignition switch, I think this is the problem right here. I been trying to get a diagram to see what the ignition switch activates along the way to key up power to the accessory wire/second half of the ignition switch.
And follow up on how you fixed this issue,currently having the same issue with my LLY, already replaced ignition switch and NSBU
 

JoshH

Daggum farm truck
Staff member
Vendor/Sponsor
Feb 14, 2007
13,105
105
63
Texas!!!
And follow up on how you fixed this issue,currently having the same issue with my LLY, already replaced ignition switch and NSBU
It is unlikely you will get a response from him since he only has the one post and hasn't been active for over 2 years, but if you can provide some details on your diagnosis, I'm sure we can help point you in the right direction. The starting circuit on these trucks isn't all that complicated.
 

Mountainman

04 lb7
Feb 8, 2020
1
0
0
I’m Having the same problem with my duramax. Have been dealing with it for a while now and haven’t been able to find the problem. It won’t crank or start sometimes and I have to use a screwdriver to the starter to get it to start but when I do that it goes into limp mode and stays in 2nd or 3rd gear and it also says service 4 wheel drive.. but when it starts with the key normally it drives with no problems. Any help please !!
 

redneckcwboy

New member
Aug 16, 2010
2
0
0
Az
Update

Here is the update,

After years of problems, the issues have been finally solved. After installing a new batteries, ignition switch, NSBU, BCM, TCM and ECM all reprogrammed to the truck and to no avail.

One of the faults was due to a loose power wire connection under the fuse box at the white connector. This solved the gear selector problem among the loss of communication with the TCM and a few other power loss related issues.

Second the ECM was replaced with a used reprogrammed module, due to faulty memory modules. I don’t know if this had any real relations to the main issues but maybe a coincidence from the power fault.

Third and final moving issue that solved the problem, one or two of the transmission speed sensors was faulty, unfortunately I don’t remember which ones. So all 3 were replaced (engine speed, turbine speed, output speed). One of the indications was that I didn’t have any turbine or output speeds (with a reader hooked up ie: snap-on, EFI) but I did not have any codes as one would think with faulty sensors.
 

BradMike

04.5 LLY XCLB
Feb 5, 2020
2
0
0
Bc, Canada
Found my issue

Okay, so my symptoms were no crank, no start, no gear selector indicator (GSI) no blower motor, no VSS, total trans limp mode. After checking fuses, and pulling inner fenders and taking the tcm out and back probing and checking grounds. I checked fuses one more time. It was the clear top 30A fuse labelled “Blower”. How ridiculous is that
 

mlucas_86

New member
Apr 19, 2021
1
0
1
having the exact issues with my 2004 lb7. No Crank NO start no gear indicator and abs light is on... replaced ignition switch, nsbu, and internal trans harness to.. still no fix......seems my ignition doesnt have power to feed to the ign 0 fuse, I did use a jumper wire from my sunroof fuse connected to the ign 0 fuse (power stays on til you disconnect this wire)- starts and runs perfect.. AND i did look for broken damaged wires by the inner fender, didnt see any at all...
 

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