2003 GMC Sierra 2500 HD, 6.0, no crank no start

Hi everyone. i am working on my neighbours 2500 HD farm truck that would just not crank one day. It has power to the starter relay but is not getting ground from PCM. When jumped it cranks but no start, it has no spark, and I don’t think the FP is working either. Very strange as whatever is wrong is affecting multiple systems. On the scanner I have throttle % but 0 V all the time for the TPS. I have 12V to the purple wire at PCM. All fuses in both panels seem good, and I see no broken wires under the fuse panel, but there were mice in there and mouse dirt/pee on the panel. Transmission switch is showing correct gear according to scan tool. The only code I am getting in p1638C, and scan tool f terminal voltage toggles 0 and 100 constantly. I have checked all the grounds I could find including the one on the passenger head. What could be common to all these circuits? I know it is rarely a bad PCM but I am beginning to wonder, though I know it is more likely a bad ground/short etc. but with 160 pins on the 2 pcm connectors, there is a lot to test, and also need to know how each one should be reading. Thanks in advance for any help.

I will have to check tonight for ground at pcm for starter. As far as lights, when I turn key to on all lights come on then all go off other than the check engine light and battery light. When turning key to crank everything is out except the CEL. I may ask the owner if he has another key on the off chance it is Passlock related but doubtful.

I would like to know if 5v reference is present at any of the 3 wire sensors

Not sure on all, but I did check the TPS today, unplugged and looking into the plug - top left to right : 0, 1.64V, 0, 1.62V, Bottom row: 4.94V, 4.81 V, 4.83V, 4.94 V.

Granted the battery is down to around 11V but is on charge now.

One thing that did make me wonder is when I was testing the plugs to the PCM, although I had some at 12V and some at 5V, I also had several at less voltage ranging from .5 to 1.5 V.

I was really hoping for a bit of help on this., I am still no further ahead. I have confirmed that I have no crank/ no spark and no injector pulse although I do have fuel pump. I purchased an Alldata subscription to get more info and diagrams, and started going through the troubleshooting tree but the info seems flawed, it is asking me to check for power from the starter enable relay control but from the diagram there should be a ground supplied. I have 12 volts all the time at relay supply voltage, and 12 volts at relay coil with key in run or crank. I have checked the common problem grounds including passenger head to firewall.

What would be involved in replacing the PCM as far as programming? I see some later GMs have had problems similar to mine and is the BCM, any help much appreciated.

Yes, that is the diagram that I have. Was going through troubleshooting steps and its telling me to check for power at the starter relay enable control which is clearly wrong - should be supply a ground.

I am really lost with this. Could it be the BCM? I know it could be as simple as a broken wire or bad ground, but it is truly being hard to track down, especially without accurate testing info. I need to know what would cause the ECM to not activate the starter, injectors and coils. I have communication, fuel pump and can activate some other things. I am seeing throttle percentage live data, as well as temps etc. as well as seeing transmission gear, brake pedal pos. etc.

So weird, as most no crank cases I see will run when you jump the relay. Also seems if it was passlock related it would start and run for a few seconds, and my theft light does not stay on.

Thanks for your interest, really needing some guidance.

I have a new scan tool ordered that should be in Friday, hoping it may help.

Yes the truck cranks when I supply the missing ground to the relay, but as I said, it has no spark or injector pulse, so something bigger is going on here than just the no crank.

I have supply voltage ( load ) at the starter relay all the time, and power to relay coil with key in run and crank. I have crank signal in to the ECM but have not checked at the ECM plug for the ground to relay , but I highly doubt it.

As I said, my troubleshooting from Alldata seems wrong.

Yes, the data now is showing me the correct gear - thats ok.

The alternator F terminal code is making me wonder if it is PCM trouble, as it is constantly switching from 0 to 100 just with key on, and this is the only code I have, and comes back instantly


I have an Xtool D8 coming, looks to be a very capable tool, so should help me see more.

I know it could easily be a bad ECM, but need to test more, I feel it could just as easily be a bad BCM, or just one bad wire/connection or short etc. Or immobilizer…lol. Shorted sensor? Will post back when I have some new info. Thanks!

Purple wire from crank fuse to pcm crank voltage. I do have power to pcm on that wire when in crank.

I will need to recheck the alternator when i get my new scanner. Yes the yellow/blk is correct.

Thanks

Do many scan tools show the starter relay status? I am disappointed that my new Xtool D8 does not, was hoping to learn something from that.


i will try checking for an RPM when jumping the relay, and also the alternator F terminal reading when I unplug the alternator.

I am going to look at it again tonight, but did not see anything related to the starter at all. Beginning to wonder if I made the wrong choice in scan tools.

Is this a module failure? First that comes to mind is,. Ebcm, disconnect that, see if you have crank, if not. There are others, HVAC, radio, ipc?

After reading that the new scanner is limited, I was thinking of common no crank problems with these trucks. It is a quick test to disconnect the ebcm

I can try unplugging the ebcm, but thought I read somewhere that the pcm needed communication with all or some modules before starting.

I did try jumping the starter at the relay with key on and there is no rpm signal.

As far as the scan tool, I was not real impressed with it on the GM, but plugged it onto my Ford and seemed to have much more information and stuff available. I was debating returning the tool and trying something else. I am not sure what people would recommend in the under $1000 range. My research led me to believe this Xtool D8 was pretty good, now not so sure. I sent an email that never got replied to and the support phone number is some 20 number long phone number in China, so looking like support is not going to be great.

Finally getting back to this truck. Returned my Xtool and got a Launch however available info is much the same. Still no info on starter request etc.

I unplugged the ebcm as suggested, no change. I unplugged the crank sensor and have close to battery voltage on green, ground on y/blk. I do have activity on the signal wire at the pcm, only using voltmeter though, no scope. There is no engine speed on the scan tool. There is 12V and ground at the coils, but no spark, also no injector pulse. Also as suggested, I fed ground to the starter relay control wire right at the pcm and it cranks, so no issues there. Though nor suspect, I tried the anti theft reset procedure and no change.

About ready to try a used pcm, local yard say they can match the number, wondering if it will be plug and play or need matching, my Launch is supposed to have some capabilities but unsure if it will in this case.

Thanks again in advance for any help. It is not hard to do basic checks, but with 160 wires to the pcm, plus possible module problems, shorted sensors, otherwise broken/shorted wires, serial data lines, there is a lot to test, and with limited resources, its being a challenge.

Did a bit more today. 12 volts at pcm from crank fuse in crank pos.

Although scan tool shows Park, would like to know how to test transmission switch inputs at the pcm. Seems like serial data and not just straight voltage?

Not sure where the info is saying there is a PID for that, but I certainly don’t see anything in the PCM or BCM on my Launch or on the Xtool D8. It certainly would reassure me if I could see that data, and was sure the new tool would show this. I am honestly faulting the truck and not the tool as this is the third scan tool I have used on this, and none had starter request data. I do have 5 V reference, at least, some, i may not have checked every one. I started going through the list of terminals at the PCM and marking my reading on each. So far thing shave checked out. ( Not sure if I mentioned that at one point I was measuring 12 volts on a couple of PCM grounds, but later it was back to ground. Thought I was crazy, but measured voltage on them twice, and also at one point checking with test light, the engine started to crank)

I have not checked the camshaft sensor yet. Early on, I was thrown off when seeing “current gear 2” on the scan tool, and thought the transmission switch was bad, I replaced it but nothing changed, and when I checked another truck, it had the same reading, so rules out the switch, though does not rule out a wiring issue between there and the pcm. I am though clearly seeing the correct gear on the scan tool data. Wish I knew what I might check for inputs at the PCM from the transmission. I can get a used pcm for $175 with the same number, but not sure if it will need matching or?

Thanks so much for your interest Monde.

P1638C is the only code. It comes back right away if cleared. Scan tool data shows Alt F terminal toggling between 0 and 100. I tried unplugging the alt. and still no start.

Hoping my Launch will be capable. Also wishing some others would chime in, this like an out of the ordinary failure. Most no cranks on the GMs that I saw in my research were simple relay failures or key switch type things or broken wires, as well as pretty common bad grounds. I wish I was so lucky.

Thank you Monde for your help. I will try to test the cam sensor tomorrow.