DTC Galore!!
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Joined: Apr 2020
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From: East Tennessee
DTC Galore!!
Hey everyone,
My car is a 2014 Z51 that has 14k miles on the clock, I have been dealing with an intermittent "Rear Axle System Off" message for a while now. So I bough myself a decent scan tool that can rear all of the GM codes and have gotten more than I bargained for on this one. I have a list!!Here goes, this is the whole car quick scan:
B26C8:00 Passed & Failed
U042B:00 Current
B067F:05 Current
B0680:05 Current
B3110:00 Passed & Failed
B3935:00 Passed & Failed
U1510:00 Passed & Failed
U0078:00 History
C0407:61 Passed & Failed
C0413:00 Current
B285A:4B History
And from the Rear Differential Control Module:
C0393:01
C0393:04
C056D:39
C056D:3C
C0800:03
C0800:07
C0805:03
C0805:07
C0870:03
C0870"07
U0077:00
U0126:00
U0151:00
U0428:71
U0428:72
U0452:71
U0452:72
U0452:74
C056D:3B
I see mention about when the C0800 is set and needing to check that first in all of the diagnostic checks in the FSM. But I have read about all sorts of fixes that have nothing to do with the charging system so I am at a loss. I have had a car at a dealership, a local GM performance shop, I have inspected the car, I am at a loss. I refuse to just start throwing parts at a problem like this without being able to identify the fault. Does anyone have a diagram or list of all the chassis grounds and I will start looking and checking for corrosion on the ones that are in the area of where works has been done on this car over the last couple of years. Thanks in advance to everyone for reading and posting suggestions!!
My car is a 2014 Z51 that has 14k miles on the clock, I have been dealing with an intermittent "Rear Axle System Off" message for a while now. So I bough myself a decent scan tool that can rear all of the GM codes and have gotten more than I bargained for on this one. I have a list!!Here goes, this is the whole car quick scan:
B26C8:00 Passed & Failed
U042B:00 Current
B067F:05 Current
B0680:05 Current
B3110:00 Passed & Failed
B3935:00 Passed & Failed
U1510:00 Passed & Failed
U0078:00 History
C0407:61 Passed & Failed
C0413:00 Current
B285A:4B History
And from the Rear Differential Control Module:
C0393:01
C0393:04
C056D:39
C056D:3C
C0800:03
C0800:07
C0805:03
C0805:07
C0870:03
C0870"07
U0077:00
U0126:00
U0151:00
U0428:71
U0428:72
U0452:71
U0452:72
U0452:74
C056D:3B
I see mention about when the C0800 is set and needing to check that first in all of the diagnostic checks in the FSM. But I have read about all sorts of fixes that have nothing to do with the charging system so I am at a loss. I have had a car at a dealership, a local GM performance shop, I have inspected the car, I am at a loss. I refuse to just start throwing parts at a problem like this without being able to identify the fault. Does anyone have a diagram or list of all the chassis grounds and I will start looking and checking for corrosion on the ones that are in the area of where works has been done on this car over the last couple of years. Thanks in advance to everyone for reading and posting suggestions!!
Last edited by mgarc1973; May 17, 2025 at 01:06 PM.
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Joined: Sep 2013
Posts: 15,665
Likes: 4,093
From: Cape Coral, Florida
First thing are these DTC’s “History” or “Current” ??…you may have had some of these codes for years…if all are history erase all and then on the next ignition cycle see what comes back…some DTC’s are called “2 Trip” DTC’s and the ECM must see 2 consecutive failures before setting a DTC…”you may need to start and drive the car a few times…Performance Shops” or dealerships don’t diagnose but simply replace parts..find a diagnostic shop in your area that has the advanced diagnostic equipment like a lab scope which is needed to diagnose a lot of issues today….FIRST thing to do is get your battery checked…those “U” are communication DTC’s and could be caused by low voltage…I’d get your charging system tested…an auto electric shop may be the best place to take your car…if I see a lot of codes like yours I look at the symptoms…you will go crazy trying to diagnose this.
Last edited by C5 Diag; May 17, 2025 at 12:45 PM.
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From: East Tennessee
C5 Tech, I agree with you, I have been going crazy with this 
haha. I will clear all of the "current" DTCs and take the car for a few drives this weekend and see what clears or comes back. As far as the "diagnostic aids" I absolutely have multiple voltage related DTCs, but the car has never been jump started, and my dad and I, who has a known good working condition 2015 Z06, have swapped batteries. Its only ever been on a battery tender over this past winter. But I will start with a voltage drop test and see what I get from that, along with checking as many ground points as I can. Not just visually, but I will take them out and inspect for corrosion. Thanks for the response and confirming my suspicion as to the direction I need to be looking!
haha. I will clear all of the "current" DTCs and take the car for a few drives this weekend and see what clears or comes back. As far as the "diagnostic aids" I absolutely have multiple voltage related DTCs, but the car has never been jump started, and my dad and I, who has a known good working condition 2015 Z06, have swapped batteries. Its only ever been on a battery tender over this past winter. But I will start with a voltage drop test and see what I get from that, along with checking as many ground points as I can. Not just visually, but I will take them out and inspect for corrosion. Thanks for the response and confirming my suspicion as to the direction I need to be looking!
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,665
Likes: 4,093
From: Cape Coral, Florida
Below is how to check your charging system…run at 2500 RPM with electrical loads on the car….checking grounds either visually or visually for corrosion is NOT how it’s done…a ground must be checked “dynamically” or with the car running with current flowing and not statically…checking grounds with an ohm meter is another mistake most DIY’ers make when checking grounds…I’d get familiar with this voltage drop checking on your grounds also.
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Joined: Sep 2013
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From: Cape Coral, Florida
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Posts: 59
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From: East Tennessee
I watched that first video almost right after you posted your first response. I will perform that later today or tomorrow. The only reason I mentioned my grounds is due to the fact that this car had been modified before I purchased it with an Edelbrock supercharged and a full exhaust and I am pretty sure some of the engine bay grounds need to be removed in order to do those installs. But like you said, a voltage drop test should easily identify if that is the case or not. I will report back with what I find later. Thanks for linking a couple good videos as well C5 Diag!!
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From: East Tennessee
So update, I performed a voltage drop test as indicated in those 2 videos, and I have from the alternator output back to the battery a drop of 0.17V max, and from the case back to the battery 0.04V. MY car after one night sits at 12.32V, but interestingly, my Dad's is sitting at 12.32V as well. When I am driving, I routinely see ~15.2V a few minutes after startup and then it'll fall to somewhere around 12.8-12.9V but will randomly spike up to 14.4-14.6V while driving. I will put my reader back on it and see if any of those codes have come back in a little bit.
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Joined: Apr 2020
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From: East Tennessee
After the voltage dropped to 12.8V on the dash as well as a second DMM the one hooked between the alternator B+ and battery was reading 0.06V. And as far as which DTCs stayed, I still have B067F:05 Current, B0680:05 Current, B3110:00 P&F, and C0413:00 P&F.
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Joined: Apr 2020
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From: East Tennessee
That was my bad, so the car finally this morning had the voltage on the DIC drop to 12.8V and I hopped out of the car and measured the voltage at the alternator and it was reading 13.05-13.1V with the display steady on 12.8V. But it took about 18 minutes of driving with the display at 14.8V before it ever started to drop.
