2002 trailblazer 4.2L no crank

#1
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_Shoot_Back

Well-Known Member
#5
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.
Was reading too fast,sry. That statement makes the ignition switch prime suspect,that is if you do see 12 volt on the red wires going into the switch.
 
#8
i installed the new oem ignition switch and i'm having the same result. also when i turn on the ignition i hear a rattling sound under the dash. funny because the monte carlo i have is having the same no crank issue and it also has a rattling under the dash.
hmmnn......
 
#9
That could be the sound of the gauge stepper motors cycling.

So you have a no crank issue. One thing that is a possibility is the VATS that has gone wonky. Is the security padlock light on or flashing?

For some reason, the PCM is not happy and not wanting to send that signal to the starter relay. One of the main reasons is a bad park/neutral switch or it's not adjusted properly. It's on the transmission. What is the PRNDL indicator showing?
 
#10
no security light on. actually no lights on dash.
the PRNDL is working correct according to the display on the dash. even when i put it in park the doors unlock. so idk
i am not getting a signal to the starter relay when the car is attempting to crank. i have to jump the relay or the signal wire on the starter
 
#13
And part 2 shows that fuse 28 blew because one of the coils went bad and shorted. Check all the fuses first! Then follow the schematics and check power and grounds.

 

budwich

Well-Known Member
#14
you need to back up. first how are you checking the fuse... with your eyes or meter? Second what FUSES have you checked (22, 34 shows in the schematic). Along with checking said fuses, check the voltage conditions in the fuse block to see whats there. Lastly, what wires at the ignition have you checked for voltage? Lucky you the a "pair of evil twins"... that way when you resolve the issue with one, the other gets "his" for free... :smile:
 
#16
And nothing at the yellow? One of two possibilities. You got a bum ignition switch (it has happened if not an ACDelco) or the teeth are off. What if you jumpered from the red to yellow wires with the ignition on? Does it crank?
 
#17
And nothing at the yellow? One of two possibilities. You got a bum ignition switch (it has happened if not an ACDelco) or the teeth are off. What if you jumpered from the red to yellow wires with the ignition on? Does it crank?
i supplied power to the yellow wire and the it still will not crank
 

budwich

Well-Known Member
#19
providing power to the yellow doesn't do much IF there is no ground supplied by the PCM for the relay to pull up. :-(

have you checked the fuses that were suggested... not sure how 28 came up... its not involved in the schematics???????
 
#20
providing power to the yellow doesn't do much IF there is no ground supplied by the PCM for the relay to pull up. :-(

have you checked the fuses that were suggested... not sure how 28 came up... its not involved in the schematics???????
i've checked the fuses. theyre good. and i also put a jumper wire on the red to the yellow with the ignition on and still will not crank
 

budwich

Well-Known Member
#22
so the last question is... how did you check for the ground? IF that check was done at the relay socket... then you need to actually continuity check from the socket to the pcm connector to ensure that you have a wire path for the ground to get there.
 
#24
so the last question is... how did you check for the ground? IF that check was done at the relay socket... then you need to actually continuity check from the socket to the pcm connector to ensure that you have a wire path for the ground to get there.
i check the purple wire that goes to the pcm from the crank fuse and have good continuity
 

budwich

Well-Known Member
#28
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.
 
#29
Going through a pretty similar issue and wondering if you've fixed it yet? My truck stalls intermittently and then won't crank. Has been for a long time and is always wire related. Instead of the shop doing more work I'm trying to figure it out with the help of this great forum.
 
#30
The PPL wire going from the crank fuse to the PCM is not getting 12v when in the run or on position. I'm not sure how to separate the fuse box and look for any breaks in there but I'm suspecting the fuse box may be causing this as it was replaced before. I'm wondering if I can just run a new PPL wire and see what that does first. I'm not getting continuity from the PCM to the crank fuse, so my break must be in that wire or inside the fuse box.

Thoughts?
 
#31
If you look back on the diagram from that fuse, it comes from the yellow wire at the ignition switch when in the START position and goes to the PCM to tell it you're commanding the starter . The PCM, if it's happy, will command the starter relay bybsending ground through the yel/blk wire to the relay and will work if the park/neutral switch is sending + to the other side of the relay through the yel wire.

Check what you're getting at the wires at the ignition switch and the other side of that relay.
 

budwich

Well-Known Member
#32
The PPL wire going from the crank fuse to the PCM is not getting 12v when in the run or on position. I'm not sure how to separate the fuse box and look for any breaks in there but I'm suspecting the fuse box may be causing this as it was replaced before. I'm wondering if I can just run a new PPL wire and see what that does first. I'm not getting continuity from the PCM to the crank fuse, so my break must be in that wire or inside the fuse box.

Thoughts?
The purple wire only gets 12v in "start", not run.
 
#33
Mooseman,
I double checked the relay starter with the key on run versus without the key. Also noticed some other things, please let me know what you think:

Ignition switch tested fine. Power at yellow wire when on start.

With the key on run the voltage drops at the relay starter:
11.9v at pins 86, 87 & 30 (IgnE, IgnA & starter)
With the key off/out:
12v at pins 87 & 30 (IgnA & starter)

NOW, I do NOT have a Yellow/Black wire going to pin 48 on the first PCM clip. There is no pin at 48 and I'm positive about that. My truck is a 2002 so this is messing me up as the diagrams show that wire. I'd be glad to post a pic as proof.

I do not get 12v at the fuse crank (fuse22) when in the run or start position. So the power seems to stop there, which is why I believe there must be a break in the PPL wire or in the fuse box.

Can anyone send me a link or attachment of removing the fuse box and separating it? I'm having trouble getting it out and afraid to screw something up.
 

budwich

Well-Known Member
#35
:-( you need to check for power at fuse 34... power always there (B+) and fuse 17 in start. As you can see in the diagram... there is lots of potential for problems going towards the ignition switch.... but again check those fuses. common problem is the fuse seat isn't good.... the pin of the fuses need to be twisted a bit to help with contact in the socket.
 
#37
If you tested at the ignition switch's yellow wire in START and getting power, you should be getting power at fuse 17 on BOTH posts of the fuse, assuming the fuse is good. This is what signals the PCM to send the signal to the starter relay.

Try this. Turn the key to RUN, then, at the fuse box, use a jumper wire from BAT+ to fuse 17. Try both fuse posts. Try pulling the fuse and using a strand of the jumper wire into the fuse sockets. If you get a response from the starter, then there is a break somewhere between the ignition switch and that fuse.
 
#40
To answer your first part. IN START, meaning turning the key like starting the vehicle, i do have 12v at the ign switchs yellow wire. I do not get 12v at the crank fuse. I do have continuity from the ignition yellow wire to fuse 17. I just triple checked all those numbers.

Does this make any sense?
 

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