NEED HELP 06 trailblazer won't start, occasionally won't crank.

4n1m4l

Member
06 trailblazer 4.2 won't start and sometimes won't crank. There is pressure (though I haven't measured how much) at the test point for the fuel rail. The only code stored is throttle body performance p1516.

So I've searched and searched, and I think I know what is going on. My trailblazer would go into limp mode and say the throttle body performance was bad. I'm thinking this is a bad wire because I took the throttle body connector off and rotated it 360 (put a different strain on the wire) and this went away. I have a new connector coming, though now it is looking like it might be right at the crimp and I don't need a new connector to fix that...

I don't think the throttle body would keep it from starting though. Trying to start it, it also sometimes won't crank, mostly when I don't try to crank immediately after inserting the key. Battery voltage is 12.6

Tldr, intermittent crank, constant no start, p1516 only code, fuel squirts out of test point, battery 12.6 volts.
 

AWD V8

Well-Known Member
By not "cranking" you mean that you turn the key to the start position and the starter will not engage, right?

Or do you mean it cranks but won't start? Meaning the starter cranks the engine over but it won't fire.

If it won't crank, then it could be the starter or neutral safety switch. Try starting it in neutral instead of park, if it's the switch it may start.
 
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4n1m4l

Member
It cranks, the engine turns over, just not every time.

I checked fuses, well, I checked that any that have 12 volts in run have 12 volts on both sides. The pcm appears to have power in run I guess I should check the ignition fuses have power as well.
 

AWD V8

Well-Known Member
Check the battery connections, clean & tight. The the ground connections also.

Likely the starter is going.
 
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4n1m4l

Member
Starter might not do it Everytime, but it cranks like a champ. I think I'm not getting ignition power.
 

AWD V8

Well-Known Member
When I was dealing with an intermittent no crank I wasn't able to diagnose it when it happened. I'd be at Home Depot and it failed to crank. I'd sit there turning the key on/off 30 times or more before it would crank. I'd get home where my tools are and it cranked every time. This happened several times a week. I finally connected a wire to the solenoid of the starter up to a test light inside my truck so I would know that at least voltage was getting to the starter, confirming that relays, switch and PCM were all working. A few days later it happened again and when it did I could see that the test light lit up but no cranking. I replaced the starter and all is well.
 
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4n1m4l

Member
Yeah. The starter was working intermittently, now not at all. So when I get a new starter I'll chase the no start. Yay.

And I have ignition power
 
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07TrailyLS

Well-Known Member
If your getting a throttle body code have you tried cleaning the throttle body? They are notoriously problematic once they get a bit of buildup on them. Pull your battery for 30 minutes after you clean the blades and see what happens
 
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4n1m4l

Member
But when it cranks it cranks like heck! I don't get it. the derating light is on solid now though
 

Mooseman

Moderator

Mooseman

Moderator
Ah, no problem :cool:

If you're getting that and a throttle code, there is a problem in that circuit. That would never be caused by a dirty throttle but it should be clean once this is figured out.

These throttle bodies aren't known to fail much but it's possible. Do check the wiring, as you said, it is suspect. If that checks out and you have a pick-a-part close by, grab yourself a throttle body and change it. It could be a loose pin inside the TB's connector.
 
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4n1m4l

Member
ohmed out all 8 pins of the throttle body connector back to the PCM good, and installed a new connector for good measure. Checked 5 volt references energized good. So a new throttle body is probably next. Going to chase the no crank condition out and verify that is the PCM telling it to not start using may03LTs video and my alldatadiy diagrams.

If the PCM is telling it to not crank because of the throttle body i'm kind of unimpressed with the decision making by gm engineering to make that a thing. Being able to start should be a "trump" card to throttle body issues.
 

Mooseman

Moderator
But because it's a "drive by wire", if there is something bad going on with it, you wouldn't want it to act like a Toyota so that may be the reason if it's preventing startup. I do know that it will not shut down an already running engine and just go into REP, which makes sense.

Another thing I remembered, there have been instances of bad fan clutches screwing up the 5V reference, which is on the same circuit as the TB. Try unplugging the fan.
 
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4n1m4l

Member
:Banghead: 4 relays were in backwards. the starter relay, the ignition relay, wsw, and hi beams.

hope nothing is toast.:badday:
 
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4n1m4l

Member
You know, I checked that the 5 volts are 5 volts, but if this is a common problem, I'll try with the fan disconnected
 

Mooseman

Moderator
Relays can be inserted either way.

It is possible that the 5v gets messed up when it's running or it's an intermittent problem. Just put that out as a possible avenue. :smile:
 

budwich

Well-Known Member
not withstanding all the things said, in terms of a "no start" as in not a "turn over" (ie. quiet), you need to be checking for ground (coming from the PCM) which cause things to happen as opposed to voltages.
 
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4n1m4l

Member
It turns over like a champ now. Tried disconnecting the fan clutch with no luck. It now has 4 codes. P2101, P1516 p0223 and one more, but noticeably they are all sensors having to do with the 5 volt references. I'm stumped. Maybe something else is dragging a 5 volt line down, but I can't tell which one. I guess I need to be able to see live data. I have an obdlink MX, but I need a program for the laptop to see all the live data.
 

budwich

Well-Known Member
so we can take from what ever you did (replaced the starter????) that you no longer have any "no turn over" issue and are onto "no fire" conditions, right? Have you checked the grounds involved? recheck the wiring at the throttle "plate". there are some basic electrical tests of the throttle body position points that you need to do to determine if the unit itself is an issue or the "feeds" are the problem.
 
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4n1m4l

Member
so we can take from what ever you did (replaced the starter????) that you no longer have any "no turn over" issue and are onto "no fire" conditions, right? Have you checked the grounds involved? recheck the wiring at the throttle "plate". there are some basic electrical tests of the throttle body position points that you need to do to determine if the unit itself is an issue or the "feeds" are the problem.
yessir, no fire.
Ignition switch?
tried that day before you posted this. Someone had already changed out the ignition switch with the autozone brand. no dice...


Today, I got a clue. Took off the air filter and tried to see if it was sucking any air. Nothing. Looked at the throttle body while cranking. Didn't move. Stuck closedTook off the throttle body, pieces are rattling around inside of it. took the cover off and pieces fell out.

Should the throttle body be able to be moved by hand? Mine cant.
 
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budwich

Well-Known Member
what do you mean "took the cover off and pieces fell out."... what cover and what pieces. I guess this means you didn't clean it when it was suggested earlier. Sounds like you found the reason why it won't start... non-functional throttle body. Good... all you need now it too either put back the "pieces" or get another unit.
 
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4n1m4l

Member
Used throttle body from a junk yard, 135, fired up on the 5th try. No codes at all. The bad fuel level sender hasn't registered yet.

The pieces looked like teeth of a gear. The new throttle body spring returns to like 30 degrees, the old one was frozen at near zero. Wife's gonna take it out now. We'll see if it holds up
 
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4n1m4l

Member
So, some throttle body codes came in, noticably after the engine warmed up. Disconnected the fan clutch and they went away.

Now the only thing that keeps it from perfection is the gas pedal. Registering some codes, cutting throttle to maybe 60%? i can still get up to 70, it just takes a while. New pedal sensor is supposedly 56 bucks. I'm gonna prove the wires out first.
 
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4n1m4l

Member
So with a new gas pedal in, and the fan clutch disconnected it still occasionally fails the throttle body wide open (chugging at idle, fine at 3.5k). I'm sending the gas pedal back, and dropping it off at brakes plus. I'll update with what they find.

P0120 pedal position a circuit, p0122 pedal position a low, p0526 fan circuit, p1516 tac performance, p2135 pedal position correlation, p0121 pedal position performance, p2101 tac motor performance
 

Mooseman

Moderator
You did disconnect the battery while replacing the TB and pedal right? It probably needs to recalibrate the whole thing with these new components.
 

Mooseman

Moderator
Nope. Just disconnecting the battery will reset things.
 

Mooseman

Moderator
No, you don't need the dealer to reset and recalibrate it.
 

Mooseman

Moderator
So if new parts didn't help and a reset, I'd be checking the wiring. What are the codes?
 
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4n1m4l

Member
P0120 pedal position a circuit, p0122 pedal position a low, p0526 fan circuit, p1516 tac performance, p2135 pedal position correlation, p0121 pedal position performance, p2101 tac motor performance

And this was with the fan disconnected
 

Mooseman

Moderator
Looks like a wiring issue with that 5v reference since they all share it. You did check all the fuses? It's not unheard of for a wire to chafe or break. Get the manuals, check the schematics and break out the multi meter.
 
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4n1m4l

Member
well now its been behaving for 4 days. Been getting the run through too, driven hard. I'm wondering, recalling back to may03lt's video for cleaning the throttlebody if i should have just applied the cleaner to a shop towel rather than spray it directly. He doesn't specifically mention it, but he never sprays the stuff on there.

If that got in bad places, it could just now be drying.
 

Mooseman

Moderator
It shouldn't affect it since there are seals for the shaft. I've sprayed it with no ill effects.
 

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