# 03 Tahoe will not turn over and start?



## Yaz

Buddy just called me and said his truck will not turn over and was running fine minuets before.

Truck has 1/2 tank of fuel
Lights, wipers, radio all work.
With key on acc- gages- fuel does not move off empty, battery moves to 12 idiot light glow normal.

When key is turned nothing happens, no click or starter will not engage. he shorted the starter and it turns over but will not start.

He checked to make sure it's in neutral.. how can he tell if it a bad neutral safty switch?

He's running down to pick up a code scanner to see if that tells anything.

Thanks for reading!


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## Matt400

Before you do anything... make sure those crummy side post terminals on the battery are *very tight*, very common trouble.


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## Yaz

No that's fine, if you read it will turn over shorting the starter. I'm wondering does the neutral safety switch not only keep if from turning over but keep the ignition from going live (energizing).


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## Yaz

here is the details from my buddy with the problems..

Hey, just wondering if you might have heard of something like this before on this era Chevys?... last
night (yes, new years eve) we stopped at the gas station and after putting in some gas the Tahoe
wouldn't start. Lights are bright, tried jumping just to be sure...no change. Checked fuses,
nothing blown. Towed it home today with a tow strap..lol.

Today in the rain: There's no voltage at the starter solenoid when the ignition is turned to the
"start" position. I can short the solenoid to battery and the starter cranks fine. With key in
"run" position it won't start even when cranking the starter by shorting it. 

My ideas so far are: (1) the alarm might be hosed up and preventing voltage to the starter solenoid,
or (2) the car lost programming for the ignition key, or (3) maybe the neutral safety switch went
bad.

We tried moving the gear selector around a bunch, disconnected battery for 1/2 or so, leaving
ignition key on in "run" position for 15 mins (neighbor said that fixed a similar problem on their
car), rechecked fuses, armed and disarmed alarm a million times, etc. Not sure what to try next. 
Any suggestions?

Do you think we should try to get a code reader to see if there are faults? Not even sure if this
car is OBDC II or what...I bet you know.  Wondering if something else failed that might prevent
it from starting...like fuel pump, etc. I'm used to cars that still crank over when something like
that dies...but not sure about this one.

Also, I noticed that when we turn the key to "run/on" position the gas gauge doesn't go up. Seems a
little strange to me. When you turn the key to the "start" position all the gauge needles actually
go to the left..almost like something is shorting out. Just wondering if that is normal or not?


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## Matt400

I did see where it would turn over when bypassing the circuit.
The battery connections are just what I see most all the time on GM's with odd electrical troubles.
Loss of full voltage to the BCM (Body Control Module) could confuse the Pass-lock security system and disallow the start. If those connections are clean and tight then the Pass-lock system may need to be re-flashed.


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## Matt400

Also there is a TSB listed for that model on no starts due to a bad harness. The TSB# is 03-08-50-014 and that could also be suspect.
The harness under the drivers seat gets chaffed as it lays on the seat track and rubs through so you could take a look at that.


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## MickiRig1

You have 2 circuits when it comes to starting a vehicle. You have the RUN circuit which everything has power. Then there is the START circuit. The start circuit only powers what you need for the vehicle to start. That's why the heat blower, wipers ect shut off when you turn the key to engage the starter. I would tend to think you have a fusible link or 2 fried in the harness. I would bet GM still uses them. It was a common problem with them for a long time. If you have a repair manual it should give you the colors of the large wires that supply each circuit. It might be the large yellow supplies the start circuit and the large red the run circuit. See if you power to them in each situation. See if your getting power to and out of the ignition switch. Go to the library and read up on the key driven security system and see if there is test procedures. The library should have the professional manuals or direct you to a branch that does.Most Motors / Chiltons etc go more in depth on the systems. The repair manuals most times you buy at a parts store do not give that much information.


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## B&B

The gauges traveling to the extreme left of their range is normal during crank so you can skip that. You can also skip any security (Passlock) issues as it only kills the fuel pump, the engine will still crank regardless. UNLESS it has an aftermarket alarm system. If thats the case, remove it.

The very first place to start is at the 10 AMP "crank" fuse in the under hood panel. Get a test light on there and turn the key to the crank position. Is there 12V on both sides of the fuse while in the crank position?

If that checks out ok the next thing to do is disconnect the connector on the NSBU (neutral safety/back up lamp switch) located on the side of the trans and first check the pink wire for 12V with the ignition in the run position. If you're good there then take a 10AMP fused jumper wire and connect that same pink wire with the dark green wire also located there and attempt to start the truck. Does it now start? If so then the NSBU switch is defective.

There's much more to check as the starting system isn't as simple as most think on all late model vehicles but we'll take you through some further diagnosis if need be.


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## Yaz

Thanks guys, I had him check the Neutral safety switch and sent him this info this morning..I'll let you all know ASAP what he finds.


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## Matt400

My bad on ther Pass-lock, it would disable the fuel injectors not your starter motor.
If you have access to a fax number, pm me the number and I can fax you a wiring diagram for the starter circuit.

When you bypassed the starter the way you did though I would think you could have a crank but no start condition because the PCM (Power-train Control Module) would not be receiving a crank signal through the 10a fuse B&B mentioned. With no crank signal the PCM would not enable the injectors.
That 10a fused circuit only has power when you are cranking and is there to tell the PCM you want to start the motor. The PCM then enables the starter relay.


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## B&B

Matt400;940878 said:


> When you bypassed the starter the way you did though I would think you could have a crank but no start condition because the PCM would not be receiving a crank signal through the 10a fuse B&B mentioned. With no crank signal the PCM would not enable the injectors.
> That 10a fused circuit only has power when you are cranking and is there to tell the PCM you want to start the motor. The PCM then enables the starter relay.


This is correct Matt however at this point we're only looking to isolate the issue. If it cranks with the NSBU bypassed then it identifies the issue.

Just dug up the starting circuit Yaz if you want it pass it on...


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## Yaz

He said the voltage is good at the "crank" fuse with ignition in start position. Couldn't get the neutral safety switch connector out without breaking the housing, so ended up removing the whole thing. Turns out both connectors appeared to be glued in..nice! He replaced the neutral safety/reverse lights switch with a new one ($37 in stock at local Kragen)...problem still exists...damn!!


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## B&B

Then follow the diagram and check for all inputs at the starter relay next, and in all actuality you should be able to physically hear the relay click when the key is turned to the crank position. Not too loud but should be audible. 

Note: the PCM crank signal to the starter relay is GROUND not battery voltage so be aware of that while testing.

The trick to removing the connectors at the NSBU switch is a heat gun. The sealing grease thats used turns to glue after a few years making removal difficult unless you warm them up first.


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## Yaz

The Tahoe is running!!! 

He bought a code scanner I told him he needs and then plugged the code scanner into the ODB II port on the Tahoe but it could not link up. His neighbor was out in his yard so he asked if I could test the scanner on his 07 Chevy 3/4 ton turbo-diesel truck. It linked right up when he tried it on his truck. Then he ended up takeing down the dash to trace the OBD II connector wires. He found that the previous owner must have installed and then removed some sort of device (radio maybe?) and had stuffed a coax cable behind the driver side fuse panel and cut off two "hot" wires that were up against a metal panel under the steering column. He removed the wires and the scanner synced up. I then turned the ignition key and it started up. Unbelievable huh? O well he has a new NSBU switch out of the deal, and he got a new code scanner..lol. he test drove the Tahoe ~12 miles and then checked codes with the scanner...none found. He thinks it is good to go now and appreciates all your help. 
Thanks you again guys!!! 
He said he will send me some pics of the harness for me to post.


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## sidthss

That is a good easy fix, if you knew what to look for, that is the problem with used cars, ya never know what was done to them before you buy it.


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## Matt400

Good job!


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## B&B

Those ones are a relief as well as a frustration at the same time. A relief because you know it's fix and frustration because it was something caused by a previous owner that you wouldn't be inclined to look for. 

Been there before myself. Issues caused by aftermarket alarms and remote starts mostly.


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## MickiRig1

*Back yard Mechanics win again !* 
I want to buy a scanner one of these days. I just use AutoZone to scan the system when the check engine lights on. Then go to Advance and buy the part after I check it out and look it up. I have had too many problems with AutoZone's stuff and staff.


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## brandie928

B&B;940107 said:


> The gauges traveling to the extreme left of their range is normal during crank so you can skip that. You can also skip any security (Passlock) issues as it only kills the fuel pump, the engine will still crank regardless. UNLESS it has an aftermarket alarm system. If thats the case, remove it.
> 
> The very first place to start is at the 10 AMP "crank" fuse in the under hood panel. Get a test light on there and turn the key to the crank position. Is there 12V on both sides of the fuse while in the crank position?
> 
> If that checks out ok the next thing to do is disconnect the connector on the NSBU (neutral safety/back up lamp switch) located on the side of the trans and first check the pink wire for 12V with the ignition in the run position. If you're good there then take a 10AMP fused jumper wire and connect that same pink wire with the dark green wire also located there and attempt to start the truck. Does it now start? If so then the NSBU switch is defective.
> 
> There's much more to check as the starting system isn't as simple as most think on all late model vehicles but we'll take you through some further diagnosis if need be.


question, if there is no power to crank fuse what would you look into next? also no power to small yellow wire coming from below ignition. I know there is problem with electrical but no sure where


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## Banksy

I hope it's been fixed or sold by now.


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## brandie928

Banksy;2015216 said:


> I hope it's been fixed or sold by now.


Same here. It's just I'm running into a similar issue and figured it's Not going to slow me down no more then my dumb truck to ask


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