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Won't crank or start - U0100 Code

Tiny
JAZZARO1
  • MEMBER
  • 2005 CADILLAC STS
Computer problem 6 cyl Two Wheel Drive Automatic 72000 miles

I have a car with 3.6L V6 and 72k miles. When brake and Start Button are pushed the dash goes black, but interior lights stay on, and will not crank/start at all(no clicking, no nothing). After 10-15 seconds, dash lights come back up as if car is running, but engine has not started. All interior lights and gauges appear to be working properly. Tried jumping the car, no go. Took the battery to be tested and it tested okay but I purchased a replacement just to be sure as the dealer had replaced the battery under warranty just 2 years before when this happened. The car still will not start. I checked the codes and only get one trouble code, U0100 "Lost communication with Engine Control Module/Powertrain control module A." I have seen several other posts on other sites regarding starting problems, but curiously, no one has posted their final resolution. Have checked all fuses and they are fine. I had been driving the car the day it started the issue. Came home shut off car, went back outside to leave and it wouldn't start. Gauges came on but went out after I pushed start button. Then it started on its own. Then it wouldn't start again. Replaced battery still no start. Guess I'm going to have it towed to the dealer. My car only has 95,000 miles on it. I'm second owner and purchased it when it had 33,000 miles. No other problems to speak of.

Thanks.
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Tuesday, June 8th, 2010 AT 3:13 PM

27 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,702 POSTS
That is weird, no one has gotten back to us on this problem. It sure sounds like a BCM to me but with having the car in front of me it's tough to tell.

When you find out can you please get back to us so it will help others?

Best, Ken
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Sunday, November 20th, 2016 AT 10:42 AM
Tiny
MRHARLEYMAN
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Yes, I had it towed to the dealer yesterday, said it would be a few days before they can get to it.
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Thursday, November 24th, 2016 AT 7:02 AM
Tiny
KEN L
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Hey,

Did you ever get the problem fixed?

Cheers, Ken
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Monday, June 5th, 2017 AT 6:12 PM
Tiny
3DALE3
  • MEMBER
  • 9 POSTS
Ken,

I am jumping in here, a year later, with the same problem. Did anybody ever respond with a solution, I just joined 2CarPros so I hope we can help each other.

Thank you, Dale
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Sunday, April 22nd, 2018 AT 4:26 PM
Tiny
KEN L
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Yes, people are not getting back it looks like but when I re-read this post it sounds more like the PCM has gone out because that is what the code is for.

Please check all fuses then I would try to find a used PCM and plug it in, sometimes they work and other times you need to have it programmed for about $130.00 at a shop

Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Monday, April 23rd, 2018 AT 12:32 PM
Tiny
3DALE3
  • MEMBER
  • 9 POSTS
Hi Ken,

You also replied to a long description of my symptoms so we might have two threads going on here for the same problem. There you suggested trying another PCM. Anyway, I am seriously thinking about buying a Pass-Through device and getting a temporary subscription to the GM software ($55.00 for three days) to flash the modules. The problem is the prices for the Pass-Through devices are all over the map, $700.00 to $2,300.00. I cannot figure out if the $700.00 version will successfully communicate with and flash the modules that I need to do. Any pearls or wisdom here?

Thanks, Dale
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Tuesday, April 24th, 2018 AT 2:44 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,489 POSTS
The only after market J2534 device I trust is the Drew Tech. Unit. It is repackaged by many companies including AESWave, AETools, and even Autel.
I opted for the Autel 908P with the wireless J2534 device. $2,400.00 to get the pass through and a new scan tool.
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Tuesday, April 24th, 2018 AT 6:21 PM
Tiny
3DALE3
  • MEMBER
  • 9 POSTS
The "new scan tool" you're referring to is the Autel tablet, correct? Then the J2534 unit is a separate pass-thru device, correct?
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Tuesday, April 24th, 2018 AT 6:45 PM
Tiny
STEVE W.
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Yes. Except Autel uses the pass through device as its interface to the vehicle as well. Or you can get the scan tool with a standard dongle and then the J2534 unit as an add on.
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Wednesday, April 25th, 2018 AT 8:38 AM
Tiny
ROBLO94
  • MEMBER
  • 7 POSTS
Has anything worked or anybody figure out what is wrong? Mine just started doing the same thing. Recently, I was at idle for about ten minutes and the car just shut off. I tried starting it and all it did was crank but not start. I did that twice. Then I waited a few minutes and tried to start again but it did not even crank, the accessory works, and when I push the start button everything goes off and about thirty seconds later the dash lights, and everything else comes on as if the car is running but it is not. There is no engine light on, just battery light and security light, and the common service tire monitor, I can scroll through the dash and see oil life, tire PSI, MPG average etc, as if the car was on. I tried jumping it, and nothing. The battery is good. I pulled the starter relay and connected a wire to start it that way and it will crank but will not start. I need help please.
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Saturday, September 1st, 2018 AT 4:56 PM
Tiny
KEN L
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Not yet, we keep pointing toward the BCM but nobody has responded. I would like to remove the electrical connectors from the BCM and PCM to check for corrosion and it could fix a connection problem was well. The BCM is the rear interrogation module in this car.

Here are the locations. Check out the diagrams (below). Please let us know what happens.

Cheers, Ken
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Monday, September 3rd, 2018 AT 12:34 PM
Tiny
ROBLO94
  • MEMBER
  • 7 POSTS
Well, I got a scanner and it is reading the code U0100. Those pictures are no help as mine is a 4.6L v8. I am leaning towards buying a new ECM and having it programmed to my car. Does that sound right?
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Tuesday, September 4th, 2018 AT 12:46 PM
Tiny
STEVE W.
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U0100 is lost communication, but it may not be the ECM. That code can be caused if another module is causing the network to shut down. It will also happen when battery power to the ECM is interrupted which is what sounds like is happening as you are losing power to the system.
The battery light being on is a clue to that as well. I would start by checking over the battery and charging system for bad or corroded connections.
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Tuesday, September 4th, 2018 AT 1:43 PM
Tiny
ROBLO94
  • MEMBER
  • 7 POSTS
I will check all the connections and wires and get back to you guys. I would also like to add that for about a week before this I was experiencing a really bad jerking in the car as I would try to speed up, say trying to merge on to a highway or pass another car type of speed up. Could that be anything related to the ECM? I read that the was a common reaction to a faulty ECM. I also checked the fuses while the car was in the running state, they all lit up expect for the V8 ECM fuse. Can this all still be caused by a faulty connection or a faulty BCM? I really do appreciate the help.
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Tuesday, September 4th, 2018 AT 3:51 PM
Tiny
STEVE W.
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That would be consistent with a bad connection or short. As the connection moves with the engine it can open/close. I would look at the areas that flex the most as well as the grounds and harness where it crosses sharp or hot areas.
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Tuesday, September 4th, 2018 AT 5:02 PM
Tiny
STEVE W.
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Just checking to see if you had found anything?
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Saturday, September 8th, 2018 AT 6:35 PM
Tiny
ROBLO94
  • MEMBER
  • 7 POSTS
No, I was not able to find anything to my knowledge. Having it towed to a shop so they can figure out what is wrong.
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Tuesday, September 18th, 2018 AT 10:20 AM
Tiny
KEN L
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Please get back to us this is a stumper.
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Tuesday, September 18th, 2018 AT 10:35 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,489 POSTS
Very possible that one of the other modules has an issue and is shutting the com lines off. They use the high speed data link to control the starter through the antitheft and BCM modules and there are multiple modules on that line. It would take a break out box and a good scan tool to read which module(s) are not being found to find the problem.
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Tuesday, September 18th, 2018 AT 10:52 AM
Tiny
ROBLO94
  • MEMBER
  • 7 POSTS
Well it has been in the shop for about two weeks they told me it is the ECM module, ordered the part online and had it programmed to my car and dropped it off to them yesterday. So hopefully we will know by today or tomorrow if that is what it is.
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Wednesday, October 10th, 2018 AT 11:26 AM

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