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david craig
david craig, Auto Mechanic
Category: Chevy
Satisfied Customers: 3285
Experience:  owner/mechanic at 3D Automotive
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What could cause a trailblazer to not crank?

Customer Question

2004 trailblazer no crank, intermittent, gauges jump and dash lights flicker when problem is present.






 [SY1]You do not need these dots.




Submitted: 1 year ago.
Category: Chevy
Expert:  david craig replied 1 year ago.

I am sorry you are having problems. First things first. Check the battery cables at the battery posts to make sure they are very clean and very tight. Check the negative battery cable where it attaches to the engine to make sure it is clean and tight. Check the large cable to the alternator to make sure itsit is tight.Then check the cable to the starter to make sure it is clean and tight.

Expert:  david craig replied 1 year ago.

Do you have a voltmeter available?

Expert:  david craig replied 1 year ago.

Ok good. First lets check the battery voltage with the car not running. should be no less than 12.5 vdc.

Customer: replied 1 year ago.

Voltage seems ok what is the next step?

Expert:  david craig replied 1 year ago.

Ok, now with the voltmeter still connected to the battery, monitor it while cranking the engine. It should not go below 9.7 volts.

Customer: replied 1 year ago.

Okay, the truck will not spin over now, it is intermittent, and yesterday it would spin but not crank today and no spin.

Expert:  david craig replied 1 year ago.

any clicking? tapping? any noise?

Customer: replied 1 year ago.

There is no noise but speedometer needle will raise up and stick also rpm needle etc, jump bounce erratically sometimes.

Expert:  david craig replied 1 year ago.

I haven't tried that yet, what would that be an indicator of?

Expert:  david craig replied 1 year ago.

If it would happen to crank, then it would indicate that your battery cranking amps are dissipated.The battery voltage can be good, but cranking amps may be shot. If it still is not doing anything after this, then the ignition switch will need to be replaced. I have seen this a lot (intermittent operation). I was just trying to eliminate all the basic electrical stuff first and save you some money, but that is what the problem is going to be.

Expert:  david craig replied 1 year ago.

battery voltage can be good, but cranking amps can be shot

Customer: replied 1 year ago.
the voltage alone could spin it that strong ?
Customer: replied 1 year ago.
I said it was intermittent ...it did spin yesterday today nothing
Expert:  david craig replied 1 year ago.

it it still isnt doing anything after this, then the ignition switch will need replaced. seen this alot( intermittent operation). i was just trying to eliminate all the basic electrical stuff first and save you some money. but thats what the problem is going to be

Expert:  david craig replied 1 year ago.

keep me posted. thanks

Customer: replied 1 year ago.

hi could you give me a link to this part maybe? i have shopped off of ebay many times if this is an acceptable place...

Expert:  david craig replied 1 year ago.

sure, give me a sec

Expert:  david craig replied 1 year ago.

ebay item

272114901396

Expert:  david craig replied 1 year ago.

once you installed the iginition switch, you will need to have a new key made and coded at the dealer so the computer recognizes the new key. just call the local gm dealer parts department and they will tell you what you need to bring them i.e. vin etc....

Customer: replied 1 year ago.

ok i thought the switch was separate from the key cylinder, is this not right

Expert:  david craig replied 1 year ago.

it is. but they key cylinder goes through the switch.

Customer: replied 1 year ago.

ok how much are these keys usually

Customer: replied 1 year ago.
Dave I'm still a bit confused on the key part the key we have does not have a chip in it ...so would we still have to recode?
Expert:  david craig replied 1 year ago.

it has to be cut to they ignition switch, so the computer recognizes that its cut correctly.... not really coded.

Customer: replied 1 year ago.
do you need numbers off of switch how does this work
Expert:  david craig replied 1 year ago.

no numbers off the switch. you have to go to the dealer and have them cut a new key. they will need the vin. you replaced the cylinder too right?

Customer: replied 1 year ago.
No was just doing switch
Expert:  david craig replied 1 year ago.

does it start?

Customer: replied 1 year ago.
No
Expert:  david craig replied 1 year ago.

is it cranking?

Customer: replied 1 year ago.
Spin no crank sorry
Expert:  david craig replied 1 year ago.

when you say spin, what do you mean?

Customer: replied 1 year ago.
Motor spins over
Expert:  david craig replied 1 year ago.

so its cranking... but not turning over

Customer: replied 1 year ago.
What are you calling cranking
Expert:  david craig replied 1 year ago.

in other words its trying to start but not starting?

Customer: replied 1 year ago.
Expert:  david craig replied 1 year ago.

ok...you had me confused this whole time. we have to check for spark, if thats good then wneed to check for fuel. before all of that, sitting in the truck, turn the key to the "on" position and listen to see if you can hear the fuel pump running for a few seconds.

Customer: replied 1 year ago.
Ok very sorry I'll get back with you
Expert:  david craig replied 1 year ago.

ok.....

Customer: replied 1 year ago.
Sometimes it is dead altogether and the needles jump all around ...I guess I should mention that as well but right now it is trying to crank
Expert:  david craig replied 1 year ago.

can`you hear the fuel pump running?

Customer: replied 1 year ago.
I just got back on this ...the truck is intermittent between being able to spin the motor over and not...now for example it does nothing when you turn the key and the needles bounce up and down
Expert:  david craig replied 1 year ago.

ok. if you pull the starter relay. put a voltmeter in each slot(with the key to the "on" position to find where there is 12 volts. there should be 2 slots with 12 volts and 2 slot with 0 volts.