No Start, No Crank, no PRNDM1

Tyler.Frazier1992

Tyler.Frazier1992
Mar 11, 2020
8
0
0
Springfield, Ohio
Hi all, new member and first time poster. I have searched the forums and haven't found a fix yet.

My issue is I have no start, no crank, no PRNDM1, no IGN 0, no power to starter relay, no power to blower motor, no power to pin 63 on TCM but 10 is good. I did check the resistance on TCM and it checked out, grounds are good. I have been doing research for a week and have replaced the ignition switch with no luck. I cannot figure this out it is driving me nuts.

It all started with I pulled the trans to fix a leak and in doing so I broke the signal stud off the starter and tried to solder it on :banghead: that didn't work. So I installed a new one yes it works I jumped the starter relay and it started. I then had no communication with the TCM or ABS control module with my scanner.

I'm stumped and am hoping someone can lead me in the right direction although I'm thinking I may have to tow her to the dealer.
 

dndj

Boost!
Apr 13, 2019
207
15
18
Oregon
Check IGN A fuse. Should be a 40A megafuse type. +12v power comes directly from the batteries through this fuse which also feeds the starter relay and the ignition switch. Feed through the ignition switch works like this: in START position, this circuit feeds the 10A CRANK fuse, in RUN position, feeds the BRAKE, 4WD, HTRC/AC, CRUISE, HVAC1, IGN 3 fuses in the left side interior fuse block, and in START/RUN/ACC feeds IGN 0, TBC IGN 0.
 
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dndj

Boost!
Apr 13, 2019
207
15
18
Oregon
When you said "no power to starter relay", which terminals?

The switched side of the relay is wired directly to IGN A, so that terminal must have 12v based on IGN A being good.

The coil side +12v on the relay comes from IGN E, fed through the NSBU switch on the trans. If no power there, suspect the NSBU.
 

Tyler.Frazier1992

Tyler.Frazier1992
Mar 11, 2020
8
0
0
Springfield, Ohio
No power to any terminal. I have an 07 classic so my NSBu is called and IMS. Its inside the transmission.
Also when I jumped power to the starter solenoid (to test the new starter and blower motor) something got hot and started smoking underneath the fuse box. I unhooked the batteries before it got to bad so I couldn't find what got hot. Since then I lost my odometer. At this point I'm doing more harm than good.
 

KyleC4

Tech
Dec 30, 2016
371
13
18
Bay Area
If you jumped it and it started smoking or getting hot then I’d think something is shorted to ground. If you replace fuses do they blow immediately? How did you jump circuits for starter check? The amperage a starter draws is quite a bit and will cause other circuits to overheat if you jumped power from another circuit from fuse block that didn’t have enough gauge wire.

And if IGN A has power, that feeds to your ignition switch so that when you key on truck it powers IGN 0. Start tracing power from ignition switch. And see why it’s not making it to fuse block in the I/P. Maybe a bad ignition switch you just replace. It’ll be white wire Pin Emout of ignition switch that sends power to IGN 0 at accy, run, and start.

And reading back now you said power at IGN A but not on any terminal at starter relay? Then ohm check from IGN A fuse leg to the leg it powers for the starter relay under hood. Because if no continuity there that would tell me that circuit is open which is a circuit board and the under hood fuse block is fried.
 

clrussell

pro-procrastinator
Sep 23, 2013
5,603
161
63
Ground the body of the Tcm

A simple wire clipped on to the fins of the transmission computer to the engine block.

See what happens
 

Tyler.Frazier1992

Tyler.Frazier1992
Mar 11, 2020
8
0
0
Springfield, Ohio
If you jumped it and it started smoking or getting hot then I’d think something is shorted to ground. If you replace fuses do they blow immediately? How did you jump circuits for starter check? The amperage a starter draws is quite a bit and will cause other circuits to overheat if you jumped power from another circuit from fuse block that didn’t have enough gauge wire.

And if IGN A has power, that feeds to your ignition switch so that when you key on truck it powers IGN 0. Start tracing power from ignition switch. And see why it’s not making it to fuse block in the I/P. Maybe a bad ignition switch you just replace. It’ll be white wire Pin Emout of ignition switch that sends power to IGN 0 at accy, run, and start.

And reading back now you said power at IGN A but not on any terminal at starter relay? Then ohm check from IGN A fuse leg to the leg it powers for the starter relay under hood. Because if no continuity there that would tell me that circuit is open which is a circuit board and the under hood fuse block is fried.
I jumped power from the battery. I just replaced the ignition switch and I'm only getting power on the three wires on the top of the clip for the ignition switch. I'm going to try another one just incase.

I will check the ohm's later tonight I'm at work right now.
 

dndj

Boost!
Apr 13, 2019
207
15
18
Oregon
And reading back now you said power at IGN A but not on any terminal at starter relay? Then ohm check from IGN A fuse leg to the leg it powers for the starter relay under hood. Because if no continuity there that would tell me that circuit is open which is a circuit board and the under hood fuse block is fried.
This. As Kyle says, IGN A is a direct connection to one terminal of the switched side of the Starter relay in the main fuse box. If you don't have 12v on one of the 4 starter relay terminals, you have fried this connection on the circuit board inside the main fuse box. You could also use an ohmmeter for continuity check from the downstream side of the IGN A fuse to the relay terminal as well. Start here. If IGN A isn't providing power to the starter relay and pin A10 on the ignition switch, a bunch of downstream stuff won't work.

This is from an LB7 but should be close on all GMT800 03-07 classic

IMG_3045.jpg
 

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KyleC4

Tech
Dec 30, 2016
371
13
18
Bay Area
This. As Kyle says, IGN A is a direct connection to one terminal of the switched side of the Starter relay in the main fuse box. If you don't have 12v on one of the 4 starter relay terminals, you have fried this connection on the circuit board inside the main fuse box. You could also use an ohmmeter for continuity check from the downstream side of the IGN A fuse to the relay terminal as well. Start here. If IGN A isn't providing power to the starter relay and pin A10 on the ignition switch, a bunch of downstream stuff won't work.

This is from an LB7 but should be close on all GMT800 03-07 classic
x2. This is really all you need to do to determine that your under hood fuse block is no good
 
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