U1000 ECU Class two Communications Failure

Tiny
ANGELA GALLACHER
  • MEMBER
  • 2003 CHEVROLET TRAILBLAZER
  • 4.2L
  • V6
  • 4WD
  • MANUAL
  • 179,000 MILES
The check engine light came on shortly after I replaced my oil pressure sending unit. Got thirty four codes the primary being U1000 (ECU Class two communications failure). The others relate to the Electronic Brake Control Module (most the codes about ABS circuits) and the Transfer Case Module and 4WD Circuits. Disconnected the negative battery terminal and left it over night to reset the computer, but the check engine light came back on. Replacement computer and modules are expensive and starting bids for diagnostics for the first hour start at $100.00 and it will likely take more than an hour to find where it is coming from with this many codes. Has anyone encountered this before? Is there a more effective way to hone in on the problem? PS. The car runs perfect without signs of trouble.
Friday, August 19th, 2016 AT 8:35 PM

6 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check your battery for clean terminal ends then have a mechanic scan for codes he should be able to hone in on what the problem is it may be a connection problem. A dealer does not have to do this any garage can removing battery cable will not reset codes any more and has not been able to since 1995.
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Saturday, August 20th, 2016 AT 6:00 AM
Tiny
ANGELA GALLACHER
  • MEMBER
  • 20 POSTS
Update: went to ace auto and they spent two hours diagnosing it after they reset codes and got it to narrow down from 34 to 5 codes. They cleaned grounding wires to rule out small factors and concluded it was the ignition switch rapidly turning on/off while the vehicle was running (as best as I can describe it) that was interrupting communications between computers. Ordered the switch and will post results for benefit of other readers.
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Wednesday, August 31st, 2016 AT 5:29 AM
Tiny
RENEE L
  • ADMIN
  • 1,260 POSTS
Sounds good, please do
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Wednesday, August 31st, 2016 AT 2:45 PM
Tiny
ANGELA GALLACHER
  • MEMBER
  • 20 POSTS
Replaced the ignition switch as recommended. When I turn the key to on, the abs, brake, and service 4wd lights are on (but not when vehicle is running). Does the computer codes need to be deleted or reset or does this mean the problem is persisting and it wasn't the ignition switch?
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Friday, September 16th, 2016 AT 12:55 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
If the lights go out when vehicle starts that is normal they are supposed to do that. If they are on when vehicle is running then it needs to be rescanned to see why.
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Friday, September 16th, 2016 AT 3:10 PM
Tiny
ANGELA GALLACHER
  • MEMBER
  • 20 POSTS
Alright, thank you. I'll up date any new developments.
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Saturday, September 17th, 2016 AT 10:06 AM

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