GLA45 AMG 4Matic - AWD System Fails Functional Tests
06-22-2016, 03:27 PM
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GLA45 AMG
GLA45 AMG 4Matic - AWD System Fails Functional Tests
I own a GLA45 AMG. I decided to test the AWD system since I camp off-road and wanted to drive the vehicle on dirt/rocky/gravel roads.
Tests
I drove it to a new subdivision where the dirt road stopped, and continued as gravel covered. I slowly drove onto the gravel with an extremely slight grade. Once all 4 wheels were on the gravel, the tires started to spin.
Only the front right and rear left tires spun. The other 2 tires did not move at all.
So, only one tire per axle was spinning while the other tire was stationary.
The car was stuck, I could not move forward. I tried Controlled Efficiency, Sport, and Manual modes. Same result. All done in the standard traction control mode.
I was able to back out in reverse.
See the pictures and video. I had the same results occur 2 other times on dirt, and sand. I didn't take video of those since I was alone.
https://drive.google.com/open?id=0B8URuP4vPk8kTi1nTzJTYjREeXM
The other test I performed, I did on the side of the road after it had snowed. I drove the car to put the right 2 tires on the soft shoulder. (grass underneath), but covered with snow. The other 2 tires were on the paved road. In this case the 2 tires in the snow spun freely without moving the car forward, or providing traction. The 2 tires that had the best traction (on the paved surface), did not move. I was alone and could not take video, but I took pictures.
https://drive.google.com/open?id=0B8URuP4vPk8ka1dUci0zY05mc1E
I brought the car to the dealership before I took video or pictures, and explained what was happening. They told me they checked out the car, and everything was working properly.
After sending them the pictures and video, I took the car in to the dealership again. This time they acknowledged the issue. They opened a PTSS in the problem reporting system. It was forwarded to Germany, and then finally to the AMG division. After reviewing my pictures & video, they closed the PTSS, reporting that "The car is operating normally as it was designed to."
REALLY!? My service advisor and service manager were as stunned as I was, since they could clearly see the problem just as I had. But, they told me they could do nothing, since this was ruled as proper operation.
I am honestly floored by three things. #1 that this $50k+ car has an AWD system with a crucial operation flaw. #2 that Mercedes/AMG does not want to acknowledge and fix the problem. #3 that Mercedes/AMG did not test the system in this way.
I have been an embedded software engineer for 20+ years. I mostly worked on data and flight systems for military aircraft. Although I have not worked on automotive stability control systems like this, I have read a great deal about it, and understand how an embedded control system like this works down to the software level.
ABS/Traction Control
The ABS system uses sensors in the wheel to determine the speed of each wheel. If the systems detects the wheel has stopped (locked up), then the system will release the brake pressure to that wheel allowing it to spin. Then reapplying the pressure to slow the wheel again. This happens quickly and is the "pulsing" felt at the brake pedal under these conditions. The traction control system is built on top of the ABS system. The difference is that when is senses a wheel spinning too fast, relative to the other wheel on the same axle, it will apply the brake to that wheel. This redirects the torque to the other wheel on the axle, sending the torque to the wheel that isn't spinning. Stability Control is a system built on top of the Traction Control to prevent a car from sliding, but that does not pertain to this issue.
The GLA has "open" differentials on both axles. Meaning there is no mechanical system that regulates wheel spin. Some vehicles either provide the capability to lock the axle (4WD - LO), while other vehicles may have a "Limited Slip" Differential (LSD) which uses some implementation of wet clutches to mechanically limit how much wheel spin is incurred. Therefore, the GLA must rely on the traction control system to regulate wheel spin. From the tests I've done, it seems clear to me that the traction control system is not functioning properly in this situation. As an embedded programmer, I strongly believe that this is a software(firmware) issue. I think a fix would exist in identifying why the algorithm is not working, and fixing it by updating the software. A software update would also be the easiest for Mercedes to implement. No parts or extensive labor. Just the time for the dealer to program the new software into each vehicle.
After talking to my local service advisor, he said that since this is a new vehicle platform, based on the A45. It is not the same as the legacy 4Matic AWD system. This is a front drive platform that was modified to send power to the rear via a transfer case & rear clutch configuration. He has never seen this issue with the historical 4Matic system.
I found a YouTube video where a test is done on an icy & uneven roadway, with similar results. The rear tire just spins freely. In this case, It seems the momentum of the car & spinning tire brings it forward, but if it had been going slower, I think it would have been stuck as well.
Another off road test:
Conclusion
Has anyone else tested their AWD systems and found that it performed similarly? What do you think about AMG's response? I read they would be adding a LSD to this car. That would likely solve the problem. So, in my opinion they looked at this issue and decided it was not worthwhile to fix this since the new model will have a fix already. I think this is a poor decision as a current owner, but so far have no recourse. I just have to live with a vehicle that I bought for its AWD especially in the snow where I drive it. So I am very disappointed and frustrated. I am not sure whether this is a GLA45 or GLA250 issue.
If enough people raise the issue to their dealers, maybe that will compel AMG to address this problem and offer a solution to current GLA owners. What do you all think?
Tests
I drove it to a new subdivision where the dirt road stopped, and continued as gravel covered. I slowly drove onto the gravel with an extremely slight grade. Once all 4 wheels were on the gravel, the tires started to spin.
Only the front right and rear left tires spun. The other 2 tires did not move at all.
So, only one tire per axle was spinning while the other tire was stationary.
The car was stuck, I could not move forward. I tried Controlled Efficiency, Sport, and Manual modes. Same result. All done in the standard traction control mode.
I was able to back out in reverse.
See the pictures and video. I had the same results occur 2 other times on dirt, and sand. I didn't take video of those since I was alone.
https://drive.google.com/open?id=0B8URuP4vPk8kTi1nTzJTYjREeXM
The other test I performed, I did on the side of the road after it had snowed. I drove the car to put the right 2 tires on the soft shoulder. (grass underneath), but covered with snow. The other 2 tires were on the paved road. In this case the 2 tires in the snow spun freely without moving the car forward, or providing traction. The 2 tires that had the best traction (on the paved surface), did not move. I was alone and could not take video, but I took pictures.
https://drive.google.com/open?id=0B8URuP4vPk8ka1dUci0zY05mc1E
I brought the car to the dealership before I took video or pictures, and explained what was happening. They told me they checked out the car, and everything was working properly.
After sending them the pictures and video, I took the car in to the dealership again. This time they acknowledged the issue. They opened a PTSS in the problem reporting system. It was forwarded to Germany, and then finally to the AMG division. After reviewing my pictures & video, they closed the PTSS, reporting that "The car is operating normally as it was designed to."
REALLY!? My service advisor and service manager were as stunned as I was, since they could clearly see the problem just as I had. But, they told me they could do nothing, since this was ruled as proper operation.
I am honestly floored by three things. #1 that this $50k+ car has an AWD system with a crucial operation flaw. #2 that Mercedes/AMG does not want to acknowledge and fix the problem. #3 that Mercedes/AMG did not test the system in this way.
I have been an embedded software engineer for 20+ years. I mostly worked on data and flight systems for military aircraft. Although I have not worked on automotive stability control systems like this, I have read a great deal about it, and understand how an embedded control system like this works down to the software level.
ABS/Traction Control
The ABS system uses sensors in the wheel to determine the speed of each wheel. If the systems detects the wheel has stopped (locked up), then the system will release the brake pressure to that wheel allowing it to spin. Then reapplying the pressure to slow the wheel again. This happens quickly and is the "pulsing" felt at the brake pedal under these conditions. The traction control system is built on top of the ABS system. The difference is that when is senses a wheel spinning too fast, relative to the other wheel on the same axle, it will apply the brake to that wheel. This redirects the torque to the other wheel on the axle, sending the torque to the wheel that isn't spinning. Stability Control is a system built on top of the Traction Control to prevent a car from sliding, but that does not pertain to this issue.
The GLA has "open" differentials on both axles. Meaning there is no mechanical system that regulates wheel spin. Some vehicles either provide the capability to lock the axle (4WD - LO), while other vehicles may have a "Limited Slip" Differential (LSD) which uses some implementation of wet clutches to mechanically limit how much wheel spin is incurred. Therefore, the GLA must rely on the traction control system to regulate wheel spin. From the tests I've done, it seems clear to me that the traction control system is not functioning properly in this situation. As an embedded programmer, I strongly believe that this is a software(firmware) issue. I think a fix would exist in identifying why the algorithm is not working, and fixing it by updating the software. A software update would also be the easiest for Mercedes to implement. No parts or extensive labor. Just the time for the dealer to program the new software into each vehicle.
After talking to my local service advisor, he said that since this is a new vehicle platform, based on the A45. It is not the same as the legacy 4Matic AWD system. This is a front drive platform that was modified to send power to the rear via a transfer case & rear clutch configuration. He has never seen this issue with the historical 4Matic system.
I found a YouTube video where a test is done on an icy & uneven roadway, with similar results. The rear tire just spins freely. In this case, It seems the momentum of the car & spinning tire brings it forward, but if it had been going slower, I think it would have been stuck as well.
Another off road test:
Conclusion
Has anyone else tested their AWD systems and found that it performed similarly? What do you think about AMG's response? I read they would be adding a LSD to this car. That would likely solve the problem. So, in my opinion they looked at this issue and decided it was not worthwhile to fix this since the new model will have a fix already. I think this is a poor decision as a current owner, but so far have no recourse. I just have to live with a vehicle that I bought for its AWD especially in the snow where I drive it. So I am very disappointed and frustrated. I am not sure whether this is a GLA45 or GLA250 issue.
If enough people raise the issue to their dealers, maybe that will compel AMG to address this problem and offer a solution to current GLA owners. What do you all think?
06-24-2016, 03:09 AM
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2020 C8, 2020 defender 110X, 2019 720S, 2014 GLK 350 4matic, 2015 escalade platinum, 2013 RRS HSELux
Did you do it manually like 2nd gear? It should work that way not in drive. It is AWD and doesn't come with center differentials or a two speed transfer case. Make sure traction control is off as well.
Last edited by sblvro; 06-24-2016 at 07:37 AM.
08-03-2016, 11:17 PM
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GLE350
@jonnyspeed70 after watching your video, it doesn't look like your traction control is even trying to brake the spinning wheels. Are there any other traction settings available? My Subaru always was able to find traction when one of the wheels started to spin.
It also looks like you're high centered on something.
It also looks like you're high centered on something.
Last edited by Machine1; 08-03-2016 at 11:24 PM.
