2002 trailblazer 4.2L no crank

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
No, it doesn't because if you have continuity from the ignition switch yellow wire too fuse 17, then you should get power at fuse 17 when you turn the key to START.

And what about what I suggested with the jumper to fuse 17?
 

budwich

Member
Jun 16, 2013
2,027
kanata
well... it does sound interesting. Hope you got a chance to try mooseman suggestion with jumping of the fuse... carefully as jumping out a fuse may be dangerous to subtending circuits / wires IF there is an issue.

Anyways, the big question would be: how exactly are you measuring things (ie. what point has which lead on the meter) because if I recall there was some "mystery" about how a meter works / is used.

I suspect a finger problem.... likely that you are measuring the fuse... ie. the red on one side and the black on the other.... with the fuse in place.... :smile:

How are you measuring voltage on the yellow? sorry for the questions but when the "observations" do not align, we need to see what "your eyes and hands" are exactly doing.
 

S13Hitman

Member
Oct 20, 2017
80
Hilton Head
Before I read budwichs post. Heres an update doing the test without the wife...
I did have power at fuse 17 in START.

The truck started when jumping from the battery+ to fuse 17.

I think I'm getting a better hang of things using the meter. I was making a big mistake by looking at the wrong PCM connector which really made things confusing.

I'll give more detail going forward but my question now:
Since it started while jumping the fuse, the wire still had continuity though. Do you still feel its the same answer considering that information?

One more thing, the truck started yesterday as I mentioned while testing, without jumping anything. While it was running I would get a tick or short sound when moving the wiring behind the fuse box. I'd imagine that is the issue but just assuming. Today the truck doesn't start without jumping anything.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I think your ignition switch is NOT sending 12V+ via the yellow wire to fuse 17. Your test with the jump to fuse 17 proved it. Restest what you're getting at the yellow wire at the ignition switch. Another test would be to check if you have 12V+ at the red wire at the switch. If you are, with the switch in the RUN position, jump from the red to yellow wires. If it starts, I would highly suspect the ignition switch.
 

S13Hitman

Member
Oct 20, 2017
80
Hilton Head
Ok thanks mooseman. Truck started this morning without jumping anything, drove kid to school and back home. It doesnt help my testing when the truck works correctly. I believe my test results wont show anything due to this.

At least i know how to jump now if the truck wont start... haha
 

budwich

Member
Jun 16, 2013
2,027
kanata
Before I read budwichs post. Heres an update doing the test without the wife...
I did have power at fuse 17 in START.

The truck started when jumping from the battery+ to fuse 17.

I think I'm getting a better hang of things using the meter. I was making a big mistake by looking at the wrong PCM connector which really made things confusing.

I'll give more detail going forward but my question now:
Since it started while jumping the fuse, the wire still had continuity though. Do you still feel its the same answer considering that information?

One more thing, the truck started yesterday as I mentioned while testing, without jumping anything. While it was running I would get a tick or short sound when moving the wiring behind the fuse box. I'd imagine that is the issue but just assuming. Today the truck doesn't start without jumping anything.
I am glad you got somewhere.... but I am not sure based on what you said above.

First you say "I did have power at fuse 17 in START".... then you say "The truck started when jumping from the battery+ to fuse 17"... this is somewhat confusing... because IF you HAD voltage at fuse 17 then there is NO need to jump from the battery to get "more voltage".... UNLESS the contact in/around the fuse and / ignition switch is so poor that there was not enough current going thru.

The stuff that mooseman is indicating is good "double checks"... but you also need to double check the fuse 17 powering when the truck does not start. IF indeed you are NOT getting voltage there during a "start attempt" then your other "double checks" will confirm things at the switch, and if you are lucky, you will find the issue.... although your "hands and eyes" still seem a bit "crossed"... :smile:
 

nrshotgun

Original poster
Member
Sep 9, 2018
13
Baton Rouge, La
you need to start over and check the conditions in the wiring from the posted diagram and state exactly what they are and when as opposed to saying "I checked and they are fine".

so with key at RUN, what are you seeing on yellow/blk and drkgrn (at pcm)?
with key in start, same question PLUS what are you seeing fuse 17 and ppl at pcm?

hopefully, this will point out something as the previous posts were too mixed with doing something and getting this... but not providing enough detail of all the electrical at the same time of the events.

yellow/blk = nothing
drk grn = ground
fuse 17 = nothing
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
The redoubtable Alumnus of GMT Nation... @MAY03LT takes some time to use the Diagram I posted early on in your Thread to break down the Power Flow through the Starter Circuit... Perhaps downloading and replaying his description of these events will assist your understanding a bit better:


...and more help comes from the VOP (Video Original Poster) from South Main Auto Channel on the "No Crank No Start" Problem Diagnosis using a TECH 2 Scanner:

 
Last edited:

S13Hitman

Member
Oct 20, 2017
80
Hilton Head
Sorry for the confusion, I'm fairly certain at this point that I have a small break inside the fuse box. Maybe I'm wrong but here's why I'm leaning that way:

My no crank, no start issue is intermittent, which doesn't help me when testing things and the truck starts without any issue. So to be clear, while you guys were giving me great advice, the truck was able to start which lead me nowhere to finding my issue(s).

So now today, Oct 12th, I'm back to the no crank no start issue. Now I'll be going back and taking everyone's advice and guidance again, being very meticulous with doing it right. A GOOD BIT OF INFO from today, I tried jumping from batt+ to crank fuse (inside the female end as well) and didn't get any response.

The reason I lean towards the fuse box, it's pulled from a junkyard, when moved/bumped it seems to make something activate or make a ticking sound.

I did order an OEM starter relay online for 10 bux, the 86 (i think) post is pushed in on mine by a quarter inch, maybe a little less. It wasn't like that before. I also grabbed an ignition switch just to test with, can return if not needed obviously.
 
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mrrsm

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S13Hitman

Member
Oct 20, 2017
80
Hilton Head
I was thinking about it, can you kindly link or point me in the direction of instructions for disassembling the fuse box? I cannot find any and I'd like to crack mine open and see if it's possible to find/fix the possible break.

Assuming there is a break...

I tried removing mine but it wasn't moving much for me, took out the 4 bolts I could find. I've been wanting to dig into mine and look at whats going on anyway, I'm off from work thank goodness today.
 

S13Hitman

Member
Oct 20, 2017
80
Hilton Head
Just put the new ign switch in and fired right up... i still feel something isn't 100% at the fuse box.

ALSO, this doesn't explain my stalling issue. Does a bad ign switch cause stalling? And my local parts store didn't have an ACDelco switch. Do i have the crappy one for now...
 

budwich

Member
Jun 16, 2013
2,027
kanata
fingers crossed... :smile: anyways, an ignition can cause any number of issues as almost all "run" powering has to go thru there at some point either in terms of control (relay operation) or directly.
 

S13Hitman

Member
Oct 20, 2017
80
Hilton Head
Driving around and stalling issue is still there. I get the ABS light first, followed by the mph needle jumping and or the rpms. Then it usually stalls right after with no engine code.
Wtf could this be.

Didnt have luck with torque doing the logging correctly last week. Wilp try to figure that out to get data.
 

Rickwalker

Member
Nov 4, 2018
1
Washington
i have a no crank issue.
to start the battery is good , the starter is good and i have to supply power to the purple signal wire going to the starter or jump the wires 86 to 30 on the starter relay socket in order to start the truck. after reading the schematic on the starting system, when you attempt to start the vehicle, it should receive a ground signal from the pcm(starter enable relay control). i am not getting a signal to that socket on the starter relay. also , the crank fuse should activate as well when attempting to start the vehicle. i am getting nothing there. I am also not getting anything out of the yellow wire on the ignition switch which is going to the crank fuse, which is a good fuse.
Any help will greatly be appreciated because i also have a 06 monte carlo with the same issue and i had to start it with a manual switch
thanks all
I have the same issue only it won't start when crossing pins 87-30 only cranks over

I have the same issue only it won't start when crossing pins 87-30 only cranks over
I meant 86-30
 

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