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u0100 help with troubleshooting

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07 Oct 2018 08:40 #23728 by 3 Gens
u0100 help with troubleshooting was created by 3 Gens
hello, first post but i read a lot around here. so i bought and am driving around a 2011 Camaro 2SS ls3 stock with a Huron single turbo already tuned to 8 lbs of boost. so i decided to change plugs and wires, taking off a plug and the heat wrap on the headers just disintegrates...so, the project begins! i pull the headers and cross pipe and re-wrap them looking around the engine bay and reading around the internet, I thought it would be smart to throw in A.R.P. head studs and LS9 head gaskets. so i put it all back together and went to start it and notice my fuel tank is reading empty and i have 3/4 a tank of fuel then i get the code u0100. did a double check on all my grounds and connections and am not sure what i am missing?

so yesterday i went found all 3 fuse boxes pulled and checked all pcm tcm bcm fuses and now my tank reads again. but i still have u0100 code

so what i think i am up against is a break in a data wire? when i bought the car i started doing some research on the turbo kit and saw mechanic and individual post expressing burnt wires so i bought a lot of high temp shielding but may have broke a wire while installing the shielding? any suggestions would be greatly appreciated!! thanks so much!! also if there is a scannerdanner type mobile electronic repair guy in the Englewood, Denver metro area i would be willing to hire to help me

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07 Oct 2018 08:57 #23729 by Tyler
Replied by Tyler on topic u0100 help with troubleshooting
Hey 3 Gens! A few questions first. Does the car start and run normally now that you've got the fuel gauge working again? If cleared, does the U0100 reset? Does your scanner indicate which module is setting the U0100?

The fuel level data gets to the instrument cluster through the low speed GMLAN from the PCM, so we know that network is at least partly intact and that the PCM is sending the data. There could still be an issue with the high speed LAN, but we'll know more about that from the above questions.

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07 Oct 2018 09:06 #23730 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
the car does not turn over and i didn't even try to clear the code after i did the fuse check i need to run over there and try.

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07 Oct 2018 09:40 #23732 by Tyler
Replied by Tyler on topic u0100 help with troubleshooting
Gotcha. The no crank symptom confirms a likely PCM issue. The U0100 code suggests that the high speed LAN is operational, but we don't know that yet.

Got a multimeter? There's a few quick checks you can do to give us a better diagnostic direction. First, turn the ignition on and find a 5V reference sensor under the hood. Something easily accessible. Pretty sure the MAP is right there behind the throttle body? Disconnect it. Connect your multimeter to B- and gently probe all three pins. At least one should have 5V.

You can also check for network integrity and activity at the Data Link Connector. First, leave the key off for two minutes. Find pins 6 and 14 at the DLC.



Switch the multimeter to ohms and gently probe 6 and 14 at the same time. What is the reading? We want to see around 60 ohms.

While at the DLC, turn the ingition on and switch the multimeter to voltage. Connect the meter to B- and check pins 6 and 14 separately for voltage. What are the readings?
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07 Oct 2018 09:47 #23733 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
Thank you i will run over there today and do this. i will respond this afternoon

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07 Oct 2018 16:34 #23760 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
My map sensor reads 7.7 volts and and I am ranging 30 to 40 mv with pins 10 and 6, and 10 and 14 and with the key off I have 0 ohms between 14 and 6

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07 Oct 2018 16:52 #23761 by Tyler
Replied by Tyler on topic u0100 help with troubleshooting
You're sure about that 7.7V reading at the MAP sensor? :huh: The 0 ohm reading between 6 and 14 is strange, too. I dunno how your code reader got the U0100 if the network is shorted to ground...

Are you still at the car? If you're positive about the 7.7V reading, then that'd suggest high resistance in a PCM ground circuit. No offense meant here, but since you had the heads off for the head studs, I'd suggest a quick visual on any ground straps before going much further.

I dunno about the Camaro, but I know most other 6.2's had computer grounds at the back of the passenger cylinder head. Plus another heavy ground cable at the front of the block, passenger side.
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07 Oct 2018 17:10 #23764 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
you cant offend me. i did go back before today and disconnected and reconnected everything i touched on top of the motor there are 3 ground locations one on the back of each head and another in the middle of the passenger side head i made sure they were all tight and made a good ground connection
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07 Oct 2018 17:41 #23769 by Tyler
Replied by Tyler on topic u0100 help with troubleshooting
:lol: Well done going over the grounds again. I was kinda hoping for a slam dunk with a loose ground, but never mind. :silly:

The readings you got at the MAP sensor are at least part of the problem. Would you mind going over all three wires again? Meter connected to B-. Let me know what each wire reads.

Depending on what you find there, we may end up heading towards PCM powers and grounds.

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07 Oct 2018 18:51 #23776 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
ok i can do that in the morning thank you again

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08 Oct 2018 18:46 #23815 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
This morning I went back and did the check again with the same results. So I decided to take some photos to show where I've done the most bending to add insulation and when doing so I was adjusting the wire harness to sit better and I heard a click of a relay then I heard my fuel level low alarm meaning I have no tank reading again. So I might have found the ballpark area of my break. Or one of them.

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08 Oct 2018 18:54 #23816 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
this area here i added firewrap 3000 and reflectant . see how close it is to the exhaust.
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08 Oct 2018 18:57 #23817 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
and herer you can see how close the ecm is to the exhaust
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08 Oct 2018 19:08 #23818 by Tyler
Replied by Tyler on topic u0100 help with troubleshooting

3 Gens wrote: ...and when doing so I was adjusting the wire harness to sit better and I heard a click of a relay then I heard my fuel level low alarm meaning I have no tank reading again. So I might have found the ballpark area of my break. Or one of them.


You're onto something! :woohoo: Perhaps that wiring was heat damaged before you owned it, and manipulating the harness caused some insulation to flake off.

While manipulating the harness, you could rig your multimeter to watch the 5V reference circuit (which was abnormally high last time around). When the readings start changing, you know you're onto something.
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13 Oct 2018 15:12 #23950 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
big update thank you for you guidance i went into the harness where i said and found a major ground that when i tightened it it turned and broke i reconnected it and my car started right up no issues to show. i have to say that scannerdanner you tube videos made me feel like i could go in there and find it i am so grateful to you Tyler for walking me through it all. again thank you so much
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13 Oct 2018 18:36 #23959 by Tyler
Replied by Tyler on topic u0100 help with troubleshooting
Sweet! :woohoo: I take it you got communication back with the ECM, and the 5V reference went back to normal? For my info, whereabouts was the ground that you fixed?

Very glad to hear she's up and running again. You can feel proud of this one - lots of professional techs would have given up or thrown a computer at it. :silly:

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14 Oct 2018 05:59 #23971 by 3 Gens
Replied by 3 Gens on topic u0100 help with troubleshooting
it was a major ground at the from of the block passenger side because i had put extra heat wrap i didn't notice when i tightened it down it turned and ripped apart inside the sheilding so it looked ok and the heat wrap made it look good as soon as i removed the heat wrap the i could see the head of the wire just flopping around this is also why i kinda had connection.unfortunately i didn't take a pic of it till i fixed it. again i cant thank you enough

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