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Codes need help

1137 Views 6 Replies 5 Participants Last post by  Ranger
# U1016 - Loss of Class 2 Communication with VCM
# U1016 - Loss of Communications with PCM
what do these mean? Where is the crankshaft sensor located and how hard is it to change?
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there are to crankshaft senors i do known that loss of commun wit pcm means your comp try disconnectin the battery for 10 mins then reconnect it
First let me say that if you don't have a real symptom, those U codes are wasting your time. Ignore them and move on.

U codes are communication codes, modules set them when they lose communication with another module. Meaning, while modules are active they send out a "SOH" or State of Health message to other modules on the bus, sort of like "checking in" to make sure they are still there.
On Class 2 systems this begins when the key is turned on, all the modules send out an SOH and the other modules that use their information note that they have received a SOH from that module for the rest of the key cycle.
If for some reason a module stops sending out a SOH message, any module that uses information from it will set a DTC in this format
U- means it's a communication code.
1- means it's a GM specific code (ANSI codes have a leading 0)
016- this is the module identifier, meaning the module that stopped sending a SOH. 016 is the PCM by the way. If you saw two instances of U1016 that means that two modules did not see a SOH from the PCM. Now if this accompanies a problem, like error messages or freaky electronic problems then you can use U codes to your advantage. If you are just checking codes for fun, and you find U codes, they are usually worthless.

Now that being said, do you have any symptoms or were you just checking codes?
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ewill3rd is right.

Anyway, codes like that will come in the format of "IPC C1016 CURRENT" You need those first three letters to see what module(s) is having the problems communicating to the PCM.
I think pulling battery power will usually set a "U" code as well.
The reasons i posted this question is because a few weeks ago i pulled into a gas station and my car suddenly died. I checked the oil tranny fluid etc. all was fine, so i contacted Onstar and had them do their diagnostic test. They said that everything was fine. Today i was driving through town and my car died again, then about 5 mins later the right side speakers cut off for about 5 or 6 secs. and now the radio wont store any of my tone settings.
Check the battery cables for clean tight connections.
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