2008 Chevy Silverado 1500 4.3 W/T

Hi yall have I got a doozy for yall Im gonna try and write this out even though Im not sure my head is even wrapped around it anymore,

2008 Chevy Silverado 1500 4.3 W/T No Crank sometimes / No Start ever

What I have is this truck sometimes things work and sometimes things do work and I do mean everything Cluster works sometimes, Securty pops up sometimes, Radio sometimes HVAC sometimes, but they all dont go out at same time sometimes some works others down and vice versa. The no crank is pretty much all the time and I have never heard it "run" (more on that later on )... When you turn the key on you always get the crank/run relay to activate but thats as far as it goes, I have managed to get it to the point of even cranking with the key when that happened I quickly grabbed my scanner to see if I had coms to it and did while I had it cranking I did check for spark which I have and I have compresseion, and fuel getting to the rail, but in that time I could not get a injector pulse or a tach reading.

What I was able to do during this short window was manually dump fuel from injectors using the scanner and when doing that hit the key and it would fire, but of course still no Injector pulse. But now I have nothing again and it varies between what works and what doesnt and never a crank or start.

So being tired and mentally wore out from it I called every shop around me to see who had the tools to figure out what the hell was going on or atleast the know how, and not sure any exist around me. Yes Yes I took it to dealer "that will be the last time I step foot on that property" anyhow they took it in spent about a week with and and $3800 later tell me they dont know whats wrong they cant get their computer to talk to mine even after replacing the PCM,TCM,Starter, Cam Sensor and ignition switch.

Got truck back popped the hood after a week off from it and looked the wireing over and it was a mess I would say 3/4 of the engine harness was just laid out nothing protecting it. Huh could be a short somewhere pulled the entire engine harness out and looked every single wire over found a few spots fixed and reloomed the whole harness , I did while it was out to ohm out every wire in it from pin to pin everything looked good no open circuits . Put that back in this evening and here I am. I just dont know where to go from here

Im just a guy who would rather learn from the problem and figuring it out, but even I know Im in over my head and time to ask for help. And Im sure this post makes absolutely no sense what so ever.

Oh, boy! You have a good one! My first question is what tools do you have access to? DVOM, Scan tool, test light, scope?

they cant get their computer to talk to mine even after replacing the PCM,TCM,Starter, Cam Sensor and ignition switch

Seems to be a communication problem.

The first thing I would do is check the resistance on pins 6 and 14 of the DLC. With the battery disconnected (some people skip this step) you want to see 60Ω.

As far as tools I have a multi meter I borrow a Mac Scanner and a test light. Yeah I have been reading on the #6 and #14 pins and 60 Ohms test no I havent done it I will tommorow when Im back at the shop and let ya know. Little background this is the newest Truck I own the other 13 have Carbs. 2 wires and a screw driver and Im good to go. :dry:

Thanks for the Images I have looked high and low for those short of opening my own Alldata or Indentfix or whatever they go by now account.

With the scanner, check to see if you have communication with ANY modules. Namely, the Body Control Module.

I do at time and I dont at times. When I do the security light is off and everything (except no crank/no start) works no codes all modules show up its not dumb anymore, but when I dont is when the security light is on and cluster doesnt work prndl, radio, hvac, guages, no crank doesnt work .. Now I say I have no coms but actually I do cause when running the system scan it shows that I have nothing and the truck is dumb. And anything can make it go one way or the other, open the door and it will go to working, sit in it and it will stop working. With things like that thats why my head when to loose connection somewhere.

I hope that makes sense.

NuckingFutsKustoms wrote: Thanks for the Images I have looked high and low for those short of opening my own Alldata or Indentfix or whatever they go by now account.

You can get a single vehicle subscriptions from Alldata or Mitchell.for $30 a year.

alldatadiy.com/buy/

eautorepair.net/Marketing/Default.asp

Thanks to Chad for posting the diagrams.

The only thing I'd add is to catch it acting up, and go over all the fuses in the underhood fuse box with an incandescent test light. Connected to B-, touch both terminals on every fuse.

Keep track of which ones have power and which ones don't. Some may not have power KOEO by design (headlight fuses, for example), but most should. The idea is to see if the run/crank relay and the powertrain relay are working or not.

NuckingFutsKustoms wrote: I do at time and I dont at times. When I do the security light is off and everything (except no crank/no start) works no codes all modules show up

You said that the dealer replaced the PCM and TCM, but couldn't communicate with them. :dry: Were they able to program the modules?

I am wondering if you are battling your original problem, AND a dealer-installed problem, (PCM/anti-theft not programmed). :woohoo:

Ignition switch can cause the same issue to the modules. Wiggle key in ignition and see if it acts up.

Also if it has a smart fuse box it can do the same thing. Check battery powers and grounds and module powers and grounds with any common connecters.

Ok on mobile so bare with me please at the truck now. For the 6 and 14 pin ohms is 61.3-5.

As far as dealer talking and programming I'm gonna assume right now they did but I have put all my old stuff back in cause obviously that wasn't the problem and well that's another issue in itself and I am able to get everything of mine to talk at times.

On the battery and ignition replaced all bat cables and replaced all ground ends and cleaned mounting points as I read that's a common problem on these. Key wiggle doesn't do anything key flip does nothing.

Scanner is connected now and on the ipc no security lite check engine is on and and air bag. Fuel gauge reads empty even though I know there is over a half a tank. Also no prndel. No radio scanner says truck is dumb and that it has nothing like abs or airbag or pcm or tcm installed there is more I'll get pics for later. It does show a bcm this time but that has been a no show as well.

My next step would be to connect a labscope to pins 6 & 14 to see what, if any, activity exists. If you don't have a labscope, I suggest taking a voltage reading of Pins 6 & 14. You should have 2.5 volts on each, with an idle network. If you find no voltage, check pins 6 & 14 for continuity to ground.

I would, also, check powers and grounds to the BCM, ECM, TCM, Cluster, etc. while wiggling harnesses, smacking the fuse box, etc.
Check all grounds by doing a ground-to-ground voltage drop test.

Have you checked voltage drop across pins 4 and 5 at the dlc? Connect red lead to pin 5 black to pin 4. You shouldn’t see any voltage besides 100 mv or so

I’m guessing abs module is the issue. Just because there common girl taking down the network. Only other thing is unplug one module at a time see if you get any change. But you’ll need to jump the data lines in the connector so you maintain 60 ohms.

Cheryl wrote: I’m guessing abs module is the issue. Just because there common girl taking down the network. Only other thing is unplug one module at a time see if you get any change. But you’ll need to jump the data lines in the connector so you maintain 60 ohms.

Jumping the data lines will drop the network down to 0 ohms which'll take the network down, and worst case smoke something.

You only need to jumper, with a 120 ohm resistor, when you unplug a module on the end of the network which has a built in termination resistor.

No jump the data lines coming in and going out of module. Eric o from south main auto has a video on YouTube

Cheryl wrote: No jump the data lines coming in and going out of module. Eric o from south main auto has a video on YouTube

I'd like to see what he did, because dead short jumping can hi to can lo doesn't sound right. If you can't post a link to the video maybe post the title so I can find it.

Cheryl wrote: No jump the data lines coming in and going out of module. Eric o from south main auto has a video on YouTube

Cheryl is NOT suggesting to short CAN+ to CAN-. But to maintain bus continuity, like this:

Chad wrote: Cheryl is NOT suggesting to short CAN+ to CAN-. But to maintain bus continuity, like this:

Oh so the can bus runs thru' each module instead of just to it. Makes sense now. Well at least having to jump hi to hi and low to low makes sense. Having 4 potential network failure points on most of the modules makes no sense whatsoever...

Ok Im back, here is where I am at. Have coms to ECM TCM and most of BCM. What I dont have coms to is my IPC , Radio, or Door locks from scanner, the locks work from the door switch though.

So I figured I would just start at what doesnt work and work on one thing at a time so I started at the Ignition switch, What I have there is 3.9 v on the white wire which If Im seeing it correctly is the 5v ref. and Im seeing 3.9v on the pink wire witch again if reading it correctly in my signal to IGN of BCM. thats in RUN postion btw, turn the key to start and I get 2.5v on white wire and 4.1v on pink. Now when I unplug the switch altogether I get 4.9v on white and 0 on pink. Since Im brain dead at this point in time that seemed weird to me so maybe just maybe it was my switch bad. I know they said they replaced it but how do I really know this. I just happen to have a new one there so changed it out right quick and still had the same thing. SO I guess its supposed to be like that??? Tommorow I suppose Ill do some origami stuff and fold my way up under the dash and back probe the BCM and see if I get the same things. Unless yall give me another direction that Im not seeing.

that seemed weird to me

:blink: Seems weird to me, too.



This is Copy & Pasted from Alldata:

Circuit Description (Key Start)

When the ignition switch is placed in the Start position, a discrete 12-volt signal is supplied to the body control module (BCM) notifying it that the ignition is in the Start position. The BCM then sends a message to the engine control module (ECM) notifying it that CRANK has been requested. The ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the crank relay. When this occurs, battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.

Not much help.