# 09 Sierra code U0100



## snowymassbowtie (Sep 22, 2013)

I had my cel come on in the past for u0449 evap solenoid after the first storm and was told its not a big deal and to just clear it until I could get under there and replace it. It has happened 3-4 times this winter. Ive been busy with snow,plowing,pushing piles back and hauling snow. needless to say I have been busy. That code would pop and disable the factory remote start from starting it. Ive cleared it and the truck wouldnt have it again for weeks,now only lasting a few days before it popped up again. It came back on the other day so I went to clear it,it cleared but in the process of clearing 0449 the dic lit up with abs module something or other,it wasnt on very long so I didnt get to write it down before it disappeared. After I cleared the u0449 the cel came back on, went thru scan process again and found Code U0100.I was able to clear it . Now it will remote start and shut back off and not allow the truck to remote start again until I clear it. In the past I noticed that my idle was high750-800 rpm,shutting it off and restarting it would go away,never thru a code though. Occasionally when stoppping then taking off it would start off in 2nd gear then quickly downshift to 1st as I accelerated. Sorry for being so long but before I wanted to give any history of any cel issues which other than what I wrote here there has been no other problems.Has anyone had this problem and what fixed it ? I wanted to check it out myself before I have to bring it in. I plan on replacing the evap solenooid this weekend,finally a weekend with no snow in the forecast.For sh--`s n giggles Im going to take battery cables off to try and reset the ecm.


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## DaBomb6988 (Sep 22, 2013)

I'm a bit confused on your post. Are you sure you have the correct code numbers? A P0449 is a evap code. Now a U0100 or a U0449 could explain some of your issues. That is if you have a U0100. A U0100: is a generic OBD trouble code. U0100 is a serious situation where the signals between the electronic control module (ECM) or the powertrain control module (PCM) and a particular module have been lost. There could also be a problem with the CAN bus wiring disrupting communications. Symptoms of a U0100 DTC code may include. Vehicle stalls and will not crank or restart OBD trouble code U0100 will be set and the check engine light illuminated Vehicle may start after sitting idle for a period of time, however, it would be risky to operate because it could fail again at a most inopportune moment.

Read more at: http://www.obd-codes.com/u0100

I would say re-scan and write down exactly which codes you have. Also exactly what is your truck? Diesel, Gas? 1500, 3500? If you do have a U0100 or U0449 it is a serious situation, get it looked asap or you could be left stranded.


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## snowymassbowtie (Sep 22, 2013)

I do apoligize for the mess I asked for help with. Ok so in the beginning of the winter the truck threw a p0449 code which is the evap solenoid issue,common problem with gm trucks. On tuesday the cel came on, I put the scanner on and found the same p0449. While I was clearing the code something happened and the dic came on with abs problem,before I could write it down it disapeared but the cel came back on. I went thru the process to clear that code which was u0100 communcation failure. I cleared the code and cel went out. I have been looking at info on the net about that code and posted about it. Being concerned about the seriousness about that code I went out and looked at the history on the scanner. When the u0100 happened there was 3 other codes, u0101,u0442 and if I remember correct the other was u0131.Ok so yesteday I pulled it in the garage and did the hard reset,disonnect positive and ground it for a few mins.,put it back together and since then its been thru 5 or 6 key cycles(drive cycles) and havent had the cel go off again. Tomorrow im replacing the evap solenoid for the p0449 code and see how it goes from there. Sorry I wasnt clearer,I panicked when I read up on the u0100 because of how serious could be. I dont know what happened while I was clearing the p0449 but thats when it all started. Maybe I did something wrong when I had the scanner hooked up ? I dunno.
Thanks for the reply I really do apreciate it. The truck is an 09 gmc sierra 2500hd with the 6.0 gas engine.


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## WSBart (Mar 4, 2015)

If it were my truck I would ignore the U codes if they only happened once while trying to scan. Sometimes the scanner will interfere with the comms in the CANBUS system causing these codes to pop up. 

If your CEL comes on again and these codes are present or historical - then the first thing to do is get your ECM reflashed. If they happen again, well good luck figuring out whats causing it.

Luckily replacement computers arent all that expensive. The worst part is being stranded.


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## snowymassbowtie (Sep 22, 2013)

*There still off*

Thats pretty much what I thought. Its gone thru many cycles since clearing them and no lites. You start getting those codes and find out what they can mean and it gets a bit scary like time to trade it in,lol.
Thanks for the reply.


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