I have 2013 Yukon Denali Hybrid with 133,000. I took it into the dealer to have them replace the module in the GM Special warranty bulletin. They came back to me with the 12V battery didn't pass the GR8. I brought it home an used a battery tester to load test it. It only dropped to 11V and still in the low green for cranking amps. I know the 12V battery is not used for cranking so don't know why that would be an issue. Question is will a weak 12V battery cause the "Service Hybrid System" message when temperature is 51 degrees or below and then shortly turn off after start of driving? The message does not come on if it is warmer. The said none of the codes mentioned in the bulletin where in the history. IE U1821 and U182A. They said the code in history was multiple low voltage codes and GR8 said CCA was 86amps.

 

A low 12V can cause almost every conceivable code. I would trust a GR8 over your tester or my tester.

If it's the original battery, it's probably due.

 

Not original. It was built in April 2015, an AC Delco 48HPG. Suppose to be 42 month full replacement, but I don't have receipt.

 

Update: After dealership told me it was the 12V battery I got a new one. I still got the "service hybrid system" on the DTC. This seems to only come on when the temperature the car sits in is below 51 degrees. Lately it has been in the 40s and 30s and the message stays on a lot longer. It goes off after some time of driving on its own or I can hit the check mark button and it goes off. After parking in the cold for awhile it comes back on when I turn the key on or when I start it up. I took it back to dealer this time letting it sit overnight outside. When the tech started it sure enough it has the error message. After some discussion they agreed to order the parts for the special service letter and will be installing when the get them in. They told me, however they do not think that is the problem. They said they think it is, to the best of my recollection, the digital serial buss module and it would cost $500 for the part, if they can find one. Apparently only two dealers in the country show they had one and none are being manufactured. What say you?

 

Update: After returning vehicle to the dealership, waiting over 2 weeks for the parts and another 2 weeks for an appointment and then another half week because they didn't have a certified mechanic available to work on it, they finally installed the APM, taking 2 days to do so. Still has error message. They say I need a Serial Data Gateway Module and it is on national backorder and not manufactured anymore. This document clearly says to not replace the SDGM because it will not solve the problem. So the symptoms are cold temperature related. It started when temps dropped to below 51 and went away for the entire day as long as it stayed above. Now the we are in the middle of winter the temps are below freezing and the "service hybrid system" message is not only on in the morning, but also comes on all throughout the day. Today it was 29 degrees and once the message was cleared it didn't return till after shutting the vehicle off and restarting. Then when cleared it stayed off. So the replacement of the APM did change the symptoms. In addition prior to the replacement I watched the voltage reading displayed and it got all the way down to 12 volts at times. Now it stays at 15 and occasionally drops to 14 when the headlights are on then goes back to 15 shortly. So that symptom changed. So the mystery is did the defective APM cause the SDGM to throw a code deep internally that can't be reset by the computer and will it eventually clear or is there something wrong with the SDGM contrary to GM? It will cost me nearly $1000 to replace that module with no guarantee that is the issue.

 

Great updates, this will for sure help somebody in the future, if it is updated through to the final resolution.
My first thought is that this current dealer may not have the expertise with Hybrids that you need?
Somebody has probably already put this hybrid diagnostic chart on here? https://gsi.ext.gm.com/gmspo/mode6/p...iagnostics.pdf
We should be able to take this guide and with a Tech2 be able to guess at least as well as your current dealership?
Do you have any other dealers close by that you could use to get a second opinion?
.

 

I'm not sure if any service centers around here have the knowledge. I chatted with GM off their website and they said they would have to escalate to specialist. That's where it stands. I'm wondering if the tech didn't know how to clear the codes internally. It doesn't have any codes at the OBD2 that I can see.

 

I would not mind having a Tech2 scanner thing. i wonder if anyone on here has bought one for a reasonable price and could recommend a source and any accessories needed to read all Hybrid codes and others?
It looks like the cheaper ones on amazon etc are "clones" and I just am not sure if that will work or not...........

 

It's my understanding if you don't have updated software you can't read the most internal information. For example they told me that the Serial Data Gateway Module was throwing an internal code. Also if any of the hybrid modules are replaced they require programming from the most up to date software kernel from GM. Doubt if that is available to anyone other than dealers.

 

Just what I thought. After many days of phone tag with GMC special services I get nowhere. Refer me back to dealership and maybe they can reach out to the tech department. I need to talk to someone that was involved in formulating the special bulletin regarding this issue. https://gm.oemdtc.com/TSB/SB-10057008-5045.pdf So next step is to disconnect the 12V battery and the hybrid battery emergency disconnect? As I said no other symptoms just a message "service hybrid system"