Hey guys. Bought a truck for my daughter as her first vehicle. 03 sierra 2500HD. It has sat for some time, 83k miles on the odo. Wasnt ran much in the last 2 years. It had fired up and ran for about 3 minutes, then shut off and now will not start or crank. Ive done a pile of work to this, but still havent figured it out. I have lights, power locks, windows ect. All works. I have power coming from the ignition switch when turning the key. I have power directly to the pcm when turning the key on the hot signal wire. I thought it was the pcm because of that test, but new pcm did not cure the issue. So when you put the key in and turn on ignition, the dash lights up. When you crank, the dash shuts off while you are cranking, although 12volt is making to the pcm and I have 12 volt at all the fuel/ignition fuses as well. All fuses have been pulled and tested. I found where mice got into the wiring under the fuse box. Chewed 5 wires. Fixed those and tore apart the entire dash and under the hood tracing wiring. No more wires are chewed. Battery is new as well. Also, you can NOT communicate with the pcm with a scanner. There is power and ground at the obd2 port and the data wire from there ohmed out as it should. I can normally get through these issues fairly easily, but this one is kicking my ass lol. Any input would be greatly appreciated

Forgot to add I jumped the fuel pump relay and it runs and primes. Also jumped the starter relay and the engine does crank, but will not start

Power to the starter when you turn the key? My uncle’s GMC would light up the dash but not even make a click or anything when you turned the key. He thought it was something major and probably overreacted by having it towed to the dealership but it turned out to be the starter that had died suddenly.

ETA, disregard you posted more info 15 seconds before I posted.

I have an 03 with the 496 big block.
They are notorious for the pins in the wiring harness to back out. Check the plugs to make sure they’re right.

You say if you jump fuel pump relay it runs?

If the scanner can’t talk to the pcm , 99% of the time it’s the pcm.

If it has an aftermarket radio in it disconnect it and see if it starts.

Doesn’t sound like a normal security issue, could try disconnecting all power and let sit for 15 min, hook up power and force a reboot.

Service bulleting from GM about battery cable bolts causing no crank conditions

with Side-Mounted Battery Terminals

Supercede:

This bulletin is being revised to update the models and provide a new labor operation number for this repair. Please discard Corporate Bulletin Numbers 02-06-04-015 and 03-06-03-006A (Section 06 - Engine/Propulsion System).

Condition

Some customers may comment on an intermittent no crank, no start condition.

Cause

This condition may be due to poor battery cable connections. Cross-threaded/stripped battery cable bolts inside the battery side post terminals may cause poor battery cable connections.

Correction

To avoid replacing the battery , do the following steps:

^ Clean the threads in the battery side post terminals using a 3/8" (# 16) NC bottom tap.

^ Replace the battery cable bolt.

The battery cable bolt is serviced separately from the cable and is available from your Parts Department. Be sure to use the correct bolt.

I had to change my ignition harness, I had a mechanic at work show me that when I was turning key not everything would light up, but if I turned the key on and off and watched the instruments when everything lit up turn all the way on and truck would start.

Find and check the run-start relay if it has one. Had similar problem caused by such before.

Longshot, but worth a try. Try putting the transmission in neutral and starting it. I’m not certain I understand all of your symptoms, so this might not truly fit the situation.

Does the vehicle have a "chip" ignition key? It sounds like the anti-theft system has disabled the crank and/or the ignition signal, possibly due to the chewed wires. Once the anti-theft system kicks in, it usually takes some tinkering by a dealership ($tealer$hip) to reset it.

2003 shouldn’t have chip. Mine does not.

I have direct hit, and it says aftermarket radios can cause this. One of the symptoms is no scan tool communication.

Yes, jump the relay it primes up

Already bought a brand new pcm. Didnt change a thing

Tried that as well. Tried the key relearn too. Factory radio

This all started when someone attempted to jump start it off another truck due to the battery being shot. Anyone that knows these years knows thats a big no. Can fry module and from what im seeing, gm daisy chained all the modules in a loop and if one fails, something like this can happen. Buddy of mine told me to locate all modules amd begin disconnecting each one until the scanner will talk to the pcm. I tried that on the radio, climate control assembly, bcm, ignition module. I havent yet found the others

Probably not the same issue but my 05 would on occasion not complete the loop for the pass key anti theft. I had to cut the wiring at the ignition switch and "teach" the pass key again. Good luck finding the fix

I tried that early on when i first started looking at this. Wasnt it. This one has me puzzled. Keep thinking its something dumb, but havent been able to get it yet. Figured id ask on here

Tag.

Good luck

Battery fuse been mentioned?

Not sure about this, but im assuming thats a main or something? I have power all through the truck

I once had one of those copper braid ground straps cause all sorts of electrical issues. Looked at it dangling a dozen times & convinced myself it could never be the problem…………..until I hooked it up.

A fuse on the main positive battery cable...have you traced that cable back?

Write Fetterman and don’t forget the drivetrain specs

When my 01 does that, it needs the battery charged or replaced. 12 V is not enough. It takes about 13V to energize the starter relay.

Do you have good spark at the plugs?

No no spark. No crank. I have power on the purple signal wire to thr pcm ehen turning the key to crank, but nothing else happens

Super helpful

No, havent traced that. Didnt think to because i have power everywhere. When i load the system, voltage doesnt drop

I replaced the battery

Because drivetrain is never helpful.

I can be of little to zero help if the problem is driven by a computer/pcm/sensor interrupt or failure. If something in that realm is shutting you down, I would be doing the plug in and pray game that many play and probably not winning. Sorry.

Do we have certainty that you have good compression on all cans and proper amount of fuel to cans as well, and more than 12v with normal amps from battery - system properly grounded?

If "yes".

If the starter does not crank, then not getting 12v to the solenoid/starter setup. Why?? Where is the interrupt?

If the plugs are not firing (how do I discern this if engine is not cranking?), then not getting sufficient voltage into the coil (why?), or not getting it out (why?) or good voltage from the coil but not getting to plugs (all of them? and why?)

Care to elaborate?

My guess is its a shorted module of some sort. Could be anyone as gm links them all together from what ive read and been told. One bad module can cause this, but trying to figure which is where i currently am. Just hoping someone has had this issue pop and had a bit of direction. Its a tough one for sure and i appreciatr everyones input so far

So what is the voltage. Should be 13.4. You previously mention 12 V.

new battery is mid 12s. Would be 13s with engine running, but its not running.

Sounds like your troubleshooting is pretty complete, but with the mouse problem another wire or 3 might have been overlooked.

Damn that soy based wire insulation. I have to repair wires on my ATV about every 18 months.

Oh yeah, there is a 12v connection post to the right of the batt. when looking from the front. It's for all kinds of garbage to be connected to. I had trouble with that connection once.

There are 4 major food groups, ECM/PCM, ABS, transmission and body modules that would mess with the CAN buss. You’ve already eliminated security lock out. Since you tried a new ECM/PCM and failed I would look to the transmission module as that one has both a limp mode and kill switch. ABS normally won’t lock you out but a shorted one could mess with the CAN buss. Go one at a time.

There is no shortcut to this problem. You need a factory wiring diagram. There are probably multiple powers and grounds to The PCM and maybe other modules as well. You need to start with a wiring diagram. You can purchase a sub to the on line auto diag. web sites , like ALData.

Yes and get correct one for drivetrain

Chit, completely forgot about the trans module

Buddy has aldata. He sent me a couple schematics, but i need more. Always enjoy working through these problems, but with work, im about to throw in the towel and tow it to his shop lol

x2 on trying to start in neutral, or at least put it in gear and then back into park. There’s a couple safety systems that prevent you from starting it if it thinks it’s in gear.

I don't remember which years this applies to but there's a ground behind the P/S pump that likes to rot off. Worth a check.

Does the check engine light come on when you turn the key on?

I thought the same thing. There are more wires chewed through somewhere.
OP did you test continuity AFTER you did the wire repairs?

Yes, all dash icons do

Yes on continuity. Cant be 100% sure i didnt miss something, but i spent a fee hours pulling harnesses and tracing everything out. Only chewed wires were directly under the fuse box

Did it look like there was mouse piss on the fuses inside the fuse box? If so there could be corrosion inside the fuse holders. Saw it on a Youtube video. The fix was a new fusebox.

Possible faulty ignition switch??

Have you checked the coils ground wire. Runs from a harness under the front diff. Saw it could be a problem from another forum.

Checked every ground i could find and tested resistance on the grounds to the battery just to see if any had a higher reading. May have to look for that one specifically

Have you burnished all the ground points at the engine block, including the starter base? I know from experience that a ground that looks fine, isn't.

I have a full set of shop manuals for that truck. If it would help, I could scan and email that troubleshooting section to you.

Buy FORD next time !

Yeah because they never have any issues at 20 years old.

Update. So was messing with the truck while my guys were at lunhc and found a couple more chewed wires in a harness under the fuse box. Found it by cutting back the loom. Never got in there because it didnt seem there was anyway a mouse could have got in there. Well fixed those 4 wires and still nothing. What changed though is I had a buddy turning the key to crank while iw as moving things again and it started to crank for about 2 seconds. Someone had mentioned earlier in here that mouse piss could ruin a fuse box. Im thinking that is exactly what has happened. Going to order a new fuse box and replace that and see what happens

Get that thing going and trip it to some other poor soul.

Absolutely

Jerk the steering wheel right to left a few times and try it!!

Which engine? The 8.1 had a fairly common issue with the crank position sensor. One of the symptoms is a crank no start scenario.

6.0 2500HD

LOL. if I was smart, but Im not. Bought this for my daughter to run the mountain here. Going to restore the truck to make it reliable for her. Shes wanted a big truck since she was a little girl and she fell in love with this one

Really sounds like you would be time ahead, not money, to have it towed in and run through. Had a very similar issue, the little buggers got up in the wiring one cold snap night. Shorted out a few minor things like the computer, the wiring harness, fuse box, sensors, etc. On a 2 week old Denali it cost $3,600 to replace all the messed up stuff. New whiz bang trucks are nice but the little wire munchers raise holy havoc with them. No matter what they are. Saw a Toyota last week sitting in a parking spot, widows going up and down, no one in it, hey mister your truck is playin musical windows, yeah, squirrels ate up the wiring last night.

If restoring just replace all of the wiring. Then it might be reliable. Start disassembling and roll on with all new wire harness.

1999 F250 7.3 Super Duty
Had the same issue as the OP a couple years ago. Turns out there is a triple relay bank, one of which is the Low Voltage Relay buried deep under the dash, behind the radio, screwed to the firewall. The Low Voltage Relay reads the voltage at the batteries and determines if there is enough to start the truck. If not, it cuts the power to the PCM.... to safeguard it. It all started with a battery terminal that looked perfect on the external, but was corroded internally. Drove me absolutely crazy for about three weeks. It was a skin scraping job getting to the relay. Looked like I had wrestled a few Bobcats.

Gunchamp - good luck with the fix. I admire your perseverance.


In any case- you are a good Dad!

Any updates?

Thanks for asking -was just today wondering the same thing.

You get that truck fixed? IF so what was the problem.

Inquiring minds want to know...

I once replaced a part and the new one was bad too, replaced that one after eliminating everything else and it worked just fine. Frustrating as all hell. Second most frustrating was a fuse that was almost completely blown but still had a thread of connection. No idea how either happened.

Is it plugged in?
Have you tried restarting?

It was probably something so simple like turning the ignition key that now he's too embarrassed to tell us.

Get a horse!

Lol, put gas in the tank.......

Was the transmission in a forward gear?

Battery installed ?

Thank you for the kind words

Sorry guys, been working on it when find time which hasnt been much lately. I do have some more info. I pulled the fuse box and unbolted all the harnesses that are on the under side. I sprayed cleaner on all terminals and reinstalled. I also found 4 more wires chewed which I fixed. I cleaned up a few more grounds I found and after all of that, it will start to crank when using the key. It actually sounds like a clunk, but the engine slowly turns over. When using the key, you can hear the solenoid on the starter clunking. Its not a bad starter though because when I go to the start relay at the fuse box and jump it, it cranks perfectly fine. So progress has been made, but I havent had much spare time the past couple weeks to go further.

Did you replace that relay?

Yes, didnt change. I took the plastic top off the relay and squeezed it together to make the connection and the truck cranks like it should. Doesnt start but I dont think it would without cranking with the key. Trying to figure out what the difference is between cranking with the key and cranking off the relay. Thats where the final problem should be. Cranks perfect off the relay, but clunks at the starter using the key. Im getting there, just need more spare time

You bypassed the coil on the relay by pinching the contacts together. There’s a 10 amp fuse with the hot wire from the switch to the clutch/park neutral safety switch that is the circuit that tells the PCM to crank. I’d be checking the neutral safety switch circuit. If you have voltage there you can add a jumper wire to the connector for the switch and see if the relay closes.

Sorry to do this but.........

Have you called Sierra?



couldn't resist.

I have hit this wall a couple times. Intermittent crank, slow crank, no crank...neutral safety switch wiring(wires appear intact but most strands were parted), and or switch(worn out internal contacts), or partially displaced pins at a multi-pin connector...enough current flow to almost close the starter solenoid completely...gives a less than satisfying thump when key switch is turned...continuity check shows good but weak "close" of the solenoid, gives no crank, barely crank or chatter....chased it once as far as replacing the flex plate/ring gear...customer was certain that the ring gear teeth were worn and not allowing proper ring gear/bendix drive engagement...nope...flexing the gear selector switch handle slightly as you hold the key to start, will sometimes demonstrate the switch alignment/worn contacts issue...not sure if the selector switch on this truck is plastic housing, mounted on the outside of the transmission, but if it is, corrosion or wear could interrupt key to start current through the neutral safety switch. Luck and endeavor to persevere.

Ive ran all through that circuit a bunch. It does crank with the key now, but it clunks at the starter, so I would say there isnt a blown fuse in that circuit. Ive looked and tested every fuse that was there

Ok, you have peaked my interest here. That is what is happening now. The clunk noise at the starter. I apologize, but I didnt quite follow what you are saying could be the issue here. What you are explaining is exactly where its at currently

If it cranks normally when you pinch the start relay contacts together, but doesn’t with the key the the start relay coil isn’t pulling in. Sorry, I am ou of this one.

Did you get the ECM to communicate? With that operating you should be able to look at signals and see what is working and what isn't. Without it operating you are just poking in the dark.


Jerry

Not "fluent" on your particular truck, but current, of sufficient amperage, must flow through the neutral safety switch, which may be a separate switch in the steering column that is actuated by the gear selector lever, or may be a switch on the side of the transmission that the selector lever cable attaches to that selects the gear you want in the transmission. That's how it "knows" it's in neutral and it's okay to send the current to the starter solenoid circuit. From there it flows to the solenoid actuating components...worn contacts, or misalignment or marginal current carrying capacity of the wiring or the internal switch contacts results in a trickle of voltage...enough capacity to show continuity...but not enough to energize the solenoid circuit, Have you tried "key to on" and using a remote starting switch? Battery (+) to solenoid actuating terminal with a push button? Going back to read all you have done/tried now.

Yes I did. Got pulled off it at work as soon as it connected and had to stop. Havent made it back there yet

Thank you for the info and have not tried that yet