Dead 12V usually causes a multitude of codes. Several of the same code number from multiple computers all complaining about low system voltage. AND MORE "U" codes... lots of them.

The U1888 is related to the main High Speed communication bus wires.

These main communication wires are tan in color and twisted. One is tan with a black stripe.

The GM dealers have a hard time figuring these out with their specialized scan tools.

However with a good quality ohm meter there is a test you can do.

At the OBD diagnostic connector, the black trapezoid that Scan Gage and others use, pins #6 and #14 are that main communication pair of wires.

If you removed or altered any seemingly unnecessary modules that had tan twisted wires to them... that could be a problem.

With the 12V battery disconnected so ALL the computers are OFF, there should be anywhere from 59 to 62 OHMs across them.

All the computers have to be asleep to do this basic test.

Have you cleared codes and seen what comes back? You have to clear Engine, Brakes, Hybrid, HV Battery, and the Transmission to get a clean sheet. The engine computer is just a SLAVE in a 2 Mode. It is n ot in charge, the Hybrid is.

I can't reinforce that enough. So if you have done any body/structure repairs near a pair of twisted TAN wires... one with a black stripe... start there. These are NOT dome light wires.

Have you removed any seemingly unnecessary modules? Have you had to do body/structure repairs? A slightly imperfect connection on one of those tan wires can cause this. A tiny single strand of copper from a chaffed tan wire touching ground for 0.040 seconds can do it.

 

I have a PoC76 in my 2009 Yukon hybrid the definition is high voltage detected what would the cause of this be

 

That code sets if the high voltage does not ramp down fast enough. Was something being worked on? Some major computer or component un-plugged before the truck was properly shut off?


You need dealer scan tool to re-set it.

 

I have a 2010 gmc sierra that the battery died i was able to jump it once after i killed it would not start at all not even by jumping it i bought a new battery and all this has been about 4 months it has been sitting in my drive way i take the battery to get it charged every few weeks or so just so it wont be without power finally have alittle money to maybe have it taken in if i have to i have checked fuses grounds had a mobile mechanic come try to diagnose the problem with no luck only code that comes up is service hybrid system anybody have any ideas or help they may be able to offer

 

You need to plug in a scanner into the OBD2 port and read the codes to even begin to troubleshoot. Tell us what codes you get.