Differential fluid change question
Thread Starter
Instructor
Joined: Jul 2020
Posts: 130
Likes: 21
From: Valencia, CA.
Differential fluid change question
I started seeing the Service Rear Axle message a while ago, I've taken my C7 to the local dealer service center twice, they seem convinced that the problem is voltage related.
I load tested my battery, I get a consistent reading of 12.5 volts and 10.5 volts under a load, the cars Performance display shows 14.5 volts while driving.
I came across a number of C7 owners who had the same message and they changed the rear diff fluid which cleared the message. My local dealer didn't check the fluid level, of course they didn't change the fluid.
Has anyone here had Service Rear Axle message and after changing the diff fluid saw the message clear? I want to sell my C7, but I don't believe anyone would be interested until I can figure out how to clear that message,
Thank you !
I load tested my battery, I get a consistent reading of 12.5 volts and 10.5 volts under a load, the cars Performance display shows 14.5 volts while driving.
I came across a number of C7 owners who had the same message and they changed the rear diff fluid which cleared the message. My local dealer didn't check the fluid level, of course they didn't change the fluid.
Has anyone here had Service Rear Axle message and after changing the diff fluid saw the message clear? I want to sell my C7, but I don't believe anyone would be interested until I can figure out how to clear that message,
Thank you !
Drifting
Joined: Oct 2005
Posts: 1,354
Likes: 717
From: Terrell North Carolina
Never had that issue & I don't think changing the fluid will help unless it is very low. You could have a ELSD problem that will give you that message. Check the fluid level & see how nasty it is, change if very low & dirty & use the GM factory fluid. If you have ELSD problems, a GM scanner will be necessary to diagnose. Others will jump in with help as well.
Racer
Joined: Apr 2005
Posts: 259
Likes: 77
From: Sierra Nevada foothills
I had that same message, it would clear after pressing the select button, only to recur some time later. No codes. Dealer suggested a differential fluid change. However I still see this message from time to time in spite of the fluid change. Think I’ll check all battery connections including the small black ground wire for tightness and strong terminals
Le Mans Master
Joined: Jun 2019
Posts: 5,481
Likes: 2,190
From: Loveland
If you are selling the car,,,,,, just change the fluid! OR,,, open the fill hole and see if you can pump more fluid in. It's not that hard. What do you have to lose? Just make sure it's full. It will be a good selling point.
Thread Starter
Instructor
Joined: Jul 2020
Posts: 130
Likes: 21
From: Valencia, CA.
Thanks for responding!
So far, I've load tested the battery, with my car parked, engine off, the voltage is 12.5, under a load it's 10.5 volts, engine running 14.5 volts.
The confusing thing is when look at the display that indicates the various levels such as tire pressure, oil temp/level, transmission fluid, etc., with my car's engine OFF it reads 8 volts, WAY TOO LOW, but with the engine running it indicated a steady 14.5 volts. I can't figure out why there's such a wide discrepancy between the battery load tester reading (ENGINE OFF) 12.5 volts and the onboard computer showing 8 volts with engine off? I have had the battery cable connectors replaced, they're tightened, 2 wire harness connectors were also replaced due to small amounts of corrosion.
So far, I've load tested the battery, with my car parked, engine off, the voltage is 12.5, under a load it's 10.5 volts, engine running 14.5 volts.
The confusing thing is when look at the display that indicates the various levels such as tire pressure, oil temp/level, transmission fluid, etc., with my car's engine OFF it reads 8 volts, WAY TOO LOW, but with the engine running it indicated a steady 14.5 volts. I can't figure out why there's such a wide discrepancy between the battery load tester reading (ENGINE OFF) 12.5 volts and the onboard computer showing 8 volts with engine off? I have had the battery cable connectors replaced, they're tightened, 2 wire harness connectors were also replaced due to small amounts of corrosion.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
How old is the battery? I see in your profile a 2014 listed. If it still has the original battery, it's toast.
10.5 volts under load is barely serviceable
12.5 volts sitting there means nothing
14.5 volts when running is what the alternator is providing.
You're post reads as though you're "load" testing the battery in the car. That is the wrong way to test it.
When the battery is shot, you start seeing readings that don't make sense, you get errant service messages, you may find features that no longer work. All kinds of stuff starts happening with these cars.
10.5 volts under load is barely serviceable
12.5 volts sitting there means nothing
14.5 volts when running is what the alternator is providing.
You're post reads as though you're "load" testing the battery in the car. That is the wrong way to test it.
When the battery is shot, you start seeing readings that don't make sense, you get errant service messages, you may find features that no longer work. All kinds of stuff starts happening with these cars.
Melting Slicks
Joined: Feb 2018
Posts: 2,177
Likes: 1,044
From: North Texas
The only way I know of to test a battery in the car is with a conductance tester.
I believe that places like AutoZone, etc, use this method as due all dealerships.
The reason why is with a conductance tester you don't have to fully charge the battery to run the test.
A load tester needs the battery to be fully charged and disconnected from the car, too time consuming, especially at a dealership or AutoZone.
I believe that places like AutoZone, etc, use this method as due all dealerships.
The reason why is with a conductance tester you don't have to fully charge the battery to run the test.
A load tester needs the battery to be fully charged and disconnected from the car, too time consuming, especially at a dealership or AutoZone.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
The only way I know of to test a battery in the car is with a conductance tester.
I believe that places like AutoZone, etc, use this method as due all dealerships.
The reason why is with a conductance tester you don't have to fully charge the battery to run the test.
A load tester needs the battery to be fully charged and disconnected from the car, too time consuming, especially at a dealership or AutoZone.
I believe that places like AutoZone, etc, use this method as due all dealerships.
The reason why is with a conductance tester you don't have to fully charge the battery to run the test.
A load tester needs the battery to be fully charged and disconnected from the car, too time consuming, especially at a dealership or AutoZone.
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Thread Starter
Instructor
Joined: Jul 2020
Posts: 130
Likes: 21
From: Valencia, CA.
How old is the battery? I see in your profile a 2014 listed. If it still has the original battery, it's toast.
10.5 volts under load is barely serviceable
12.5 volts sitting there means nothing
14.5 volts when running is what the alternator is providing.
You're post reads as though you're "load" testing the battery in the car. That is the wrong way to test it.
When the battery is shot, you start seeing readings that don't make sense, you get errant service messages, you may find features that no longer work. All kinds of stuff starts happening with these cars.
10.5 volts under load is barely serviceable
12.5 volts sitting there means nothing
14.5 volts when running is what the alternator is providing.
You're post reads as though you're "load" testing the battery in the car. That is the wrong way to test it.
When the battery is shot, you start seeing readings that don't make sense, you get errant service messages, you may find features that no longer work. All kinds of stuff starts happening with these cars.
I've read through numerous tech articles and watched repair shop videos where they use expensive, advanced equipment, saying that under a load the battery should not drop below 9.6 volts. I took my C7 to AutoZone for a test, their results indicated that the battery, starter and alternator are fine. My local dealership repair shop replaced the battery cable connectors after finding a "voltage issue", they also replaced 2 harness wire connectors that had small amounts of corrosion, they didn't find any issues with the battery afterwards. I checked the cables to make sure there's nothing loose. The battery was replaced approx 2 years ago, I don't drive it very much, I never track my car, and when it sits undriven I use a trickle-charger. I tested the battery with cables connected and with all cables disconnected, nothing connected to the car. What I'm puzzled by is the battery voltage indicated on the display in my car reads 8 volts ENGINE OFF, and 14.5 ENGINE ON/DRIVING, while the voltage meter and load tester indicate 12.5 volts ENGINE OFF, I don't know why there's such a wide discrepancy.
Last edited by Raggaemon; May 4, 2024 at 03:24 PM.