Trailblazer cranks but wont start

Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
Hoping someone has suggestions on what I should try. My 2003 trailblazer started flashing its abs and parking brake lights and then rattled but after that was driving fine. Once I stopped it when I tried starting it later on it cranked but wont start. There's no fuel pressure bc the pump wont turn on and relay isnt flipping. Checked fuel pump with a direct connect and it works. Fuel filter is good as well. I sprayed started fluid and there is a spark and oil pressure goes up to 40. Dont know what to check next.
 

mrrsm

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Oct 22, 2015
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Try Swapping the Fuel Pump Relay (#41) with the Horn Relay and see if it Cranks... if it does... Replace the FPR.

EDIT:

Sorry about the "Crank vs. START" ambiguity... I should have said ... "Starts Up and Runs...". Mea Culpa.
 
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budwich

Member
Jun 16, 2013
2,027
kanata
:-(... are you saying that when you changed out the FP relay (with another), the engine no longer cranks? perhaps the next check would be a fuse.
 

northcreek

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Jan 15, 2012
3,310
WNY
Having trouble following this, you first said that it cranked but, wouldn't start, then you swapped relays and said that it wouldn't crank...is this correct?
 

mrrsm

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If you have even a Basic Scanner.... or can pick one up from Autozone... Knowing the Code(s) History would be a big help. As good as many of our Members here are with figuring out things... I doubt that we have any Clairvoyants among us. Have you done any very recent repairs or changed anything from being "Stock As A Clock" as per the Radio, HIB, etc...?

Here are some Very Basic Wiring Diagrams of the Starter Circuit... please take note of the divergence (Gray Wire) for the Security and the fact that this Class 2 Signal Wire goes to the PCM and is necessary to give permission for the Fuel Pump to engage. If you have had to work around the Ignition Switch at all recently... something may have gotten disturbed in that area.

Try moving the Steering Column Height Adjustment throughout its full range and... Very Carefully remove the Ignition Key...and insert/remove it in the Key-Lock Cylinder a few times... then try again to get the vehicle to start. If it does.... move the Steering Wheel up and down...Gently...and see if the engine cuts off. Does anybody else drive this vehicle... and what is your present mileage?

Tell us about anything else that has gone sideways with this vehicle to update other possible related issues. You will need a decent OBD2 Code Reader to help us out here:

 

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Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
I swapped it and it doesn't crank.
Having trouble following this, you first said that it cranked but, wouldn't start, then you swapped relays and said that it wouldn't crank...is this correct?[/QUOTE
No sorry, it still cranks but doesnt start

I pulled the tank to test the fuel pump. I powered it with an external power source. It works fine. I also checked the pinch point between the body and the frame right above the tank. The wires look good. I am able to get it to start briefly with starter fluid so it has spark. The relay is good i tested with 12 volts to trip it
So as of now. When i go to turn it over. It cranks. The fuel pump relay doesnt tripi also tryed to tap the lead on the relay to the pump with 12 volts to manually trip it but no change. Is there anything between the relay and the fuel pump like A safety switch or is it direct? When does the ecm trip the fuel pump relay during the starting process?
 

mrrsm

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We all admire the work you have done so far... but unfortunately... with an Electronically Controlled, PCM Dominated Vehicle... the Diagnostic Cascade does not allow for any sort of Old Style, "Seat of the Pants" kind of analysis. Without knowing those Trouble Codes to steer this ship... everyone on board with you trying to help out... will be dead in the water. Your next 'Port of Call'... should either be to head over to the local Autozone for the least expensive OBD2 Code Reader...or perhaps to make a phone call to a friend that will loan you his Code Scanner.

Right now... you could be chasing Ghosts in the Fuel System that may not even exist...and have troubles in other locations that at the moment... can only be guessed at. You should seek out and look at any one of the posts made here at GMT Nation by one of our Elder Statesmen... @Mooseman ...and look at the bottom of any of his postings for his Links to (...and Access Instructions into the FTP Site) the Service Manuals... and after downloading the one that covers your particular vehicle... search within that PDF for Trouble-Shooting the Engine for No Start Issues.
 
Last edited:

budwich

Member
Jun 16, 2013
2,027
kanata
You just need to turn the key to on to get the pump to run.... it will run for a few seconds and then the pcm will turn it off.

As you can see from the posts that you caused a bit of confusion with the "no crank report" and people started thinking about the starting circuit.

Anyways, you should check your fuses as your initial report about "lights flashing" (on dash) might be signs of some powering issues.

Of course.... we are likely looking in the WRONG place. Check your grounds especially since you said that you jumped the coil of the relay (if I understand your description) and the relay DID NOT operate.... that leaves only the ground as missing which could explain the other things.

Re-reading your "jump of the pump" which failed to start the pump.... your pump is either dead or the wiring to the pump is broke.
 
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Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
I have run the scan It had no codes. It did have a p014 last week but nothing since The abs and break light were flashing when i was breaking. I stopped at one store. When i started up it did a sputter/ hesitation the was running fine. I stop at the next location. Turn it over and nothing. Since the scanner didnt show any codes i took the old school method of troubleshooting the issuethe be sure it wasnt a mechanical issue. I saw on an othe forum a mention of the oil pressure switch. I will look at the mooseman links.
 

mrrsm

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Oct 22, 2015
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This might be considered "An Accidental Discharge" of the 'Parts Shotgun'... But I figure... What The Hell... You have made no progress yet and the problem remains unsolved ... Plus ... you've got two out of the three symptoms evident here with the ABS/Brake Lights ON the Dash Panel...and even though you have not mentioned any Blower Motor problems yet... with only those two symptoms along with your "Cranks-But-No Start" Scenario... If you have not as yet replaced the Ignition Switch with an OEM ACDelco flavor as depicted in this Video... THIS just might be worth a try. The Trailblazer-Envoy Ignition Switch can often go sideways and not throw any specific codes to identify IT as being the problem. Please remember... Using an OEM only part for THIS R&R is Best:

 

northcreek

Member
Jan 15, 2012
3,310
WNY
Have you tried disconnecting the battery for a bit and then reconnecting? might be worth a try.
 

Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
The ignition switch was replaced tonight but still the issue remains. I pulled the old switch out and it had buildup on the contacts so i figured might as well. Im trying to keep the "parts shotgun " in the case. Untill i can narrow down what the issue could possibly be. If anyone has the witing diagrams that would be helpfull.
 

Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
Just grab the manuals. Link is in my sig.
 

Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
Mooseman. These diagrams are gold. The wiring diagrams are exactly what i need. I will do some proding and testing tonight and give an update with the results. thank you
 

budwich

Member
Jun 16, 2013
2,027
kanata
I pulled the tank to test the fuel pump. I powered it with an external power source. It works fine. ...... The relay is good i tested with 12 volts to trip it
So as of now. When i go to turn it over. It cranks. The fuel pump relay doesnt tripi also tryed to tap the lead on the relay to the pump with 12 volts to manually trip it but no change. Is there anything between the relay and the fuel pump like A safety switch or is it direct? When does the ecm trip the fuel pump relay during the starting process?

What does the "no change" mean? does the relay operate with the "tap of 12v" to it. Does the pump operate there after... or just nothing... as the relay does not operate with the "tap of 12v"?
 

Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
Ok so a little background on the fuel system. I replaced the pump 3 months ago due to rusty leaking lines. The pump came with a harness adapter(the fuel pump pluge is larger than the tb fuel pump connector. 2 days after i got a code about the evap canister. So i went under to check. Noticed that the intake tube was broke at the tank( this is a known defect in earlier models and is covered under a special warranty). I had the tank replaced at the dealer. All good. Untill saturday when it stopped running. today i pulled out the good multimeter. The other was a cheepo that melted when i got gas on it
I checked the voltage on the relay (the lead going to the pump. When i turn the ignition on i get 12 volts to that point for 3 seconds. So i set the tester on the wire harness side of the fuel pump connector. I checked continuity from the relay to the end of the wire harness plug. The circuit is closed and i get 12 volts there. I tested the pump with a 12 volt power source and it sings. So I get voltage to the end of the wire harness. And the pump works. Also i tested the resistance of the pump. Almost zero. But when i test resistance at the relay(fuel pump connection. It shows an an open circuit.So now im thinkin it could be a bad connection I am going to get a new female end tomorrow and test with a wire going from the relay to the pump. Will update after. Again thanks to all who have contributed to the resolution of this no start issue
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Certainly sounds like a wiring or connection issue. Did you check the ground?
 

budwich

Member
Jun 16, 2013
2,027
kanata
when you tested the pump with "12v power source and it sings"... where was the 12v connected AND where was the other end (ie. ground) connected? IF you measured an open at the "out" of the pump relay... then it is likely that your ground (which doesn't come back anywhere near the fuse / relay box) is bad.
 

Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
update time. I solved the problem. It was the fuel pump connector on the chasis side. To test i ran seporate wired from the relay to the pump wire. And it fired right up. Unfortunately its snow time here so ill have to wait to get the harness spliced in. Thanks again for everyone who contributed to this issue.
 

northcreek

Member
Jan 15, 2012
3,310
WNY
Good work!..so do you think that the "flashing its abs and parking brake lights and then rattled" were just a coincidence ?
 

mrrsm

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Oct 22, 2015
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Phenompc

Original poster
Member
Mar 18, 2018
10
Long island
The abs unit is right in front of the gas tank and shares the same wire harness so it could be coincidence. Let just hope it is. My obd scanner reads abs codes and there were non stored. Its possible that the loose connector was sending power spikes down a common wire.
 

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