2003 GMC Sierra 2500 HD, 6.0, no crank no start
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"Ground cannot be checked with a 10mm socket"
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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.
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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.
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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.
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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.
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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!
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I will need to recheck the alternator when i get my new scanner. Yes the yellow/blk is correct.
Thanks
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i will try checking for an RPM when jumping the relay, and also the alternator F terminal reading when I unplug the alternator.
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- ontheriver
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- ontheriver
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I did try jumping the starter at the relay with key on and there is no rpm signal.
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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.
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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?
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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.
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Thank you Monde for your help. I will try to test the cam sensor tomorrow.
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