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Discussion Starter · #1 ·
I have an issue and I need some expertise to help me fix it. My 2017 GLA 45 is now stage 2 and every time I use Race Start (Hard launch control) it says "4matic currently unavailable" at the end of 1st gear and power completely cuts off until I let my foot off the gas. The only way I can launch the car without power cutting off is just brake boost, but it doesn't launch as hard as race start. never had the issue when I was stock. I got wider tires 245/40/20 and I still spin but not as much, message still shows up and power cuts off. should I get wider tires? My gearbox is around 80-90 when I've been driving for a while. I get the message even when the temps are 50-70C. I can get an aftermarket gearbox radiator if overheating of the clutch is really the issue here. Third option would be getting my TCU tuned by Eurocharged. Is this issue happening due to losing traction, overheating gearbox, or need a transmission retune? Which option would fix my issue? Any other options out there? Help is welcomed. Thanks all
 

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I don't know how you can troubleshoot well. Do you know if the car loses traction shifting into 2nd? Can you tell if the tires are spinning? What tires do you have? Is the compound sticky? Sticky compound will help more than an extra 10mm of contact patch.

No sensor on the clutch that I know about you can datalog. Maybe there is? but my basic OBD software doesn't have an option to log anything with the clutch.

I think I would focus on tires and traction most. And consider not using race start, but that might not be in your plans :) I will say that with 200TW 245 tires, I can still spin in race start so acc times are weak, but my car didn't dump the 4matic. But that is a dataset of 1, and I don't race start anymore so it's a grain of salt.....
 

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AFAIK the message is due to the 4matic system overheating. Something that the computer is monitoring that the user doesn’t get to see. There’s a point in engineering where the end user gets cut off from seeing some parameters that are monitored/logged.. usually for the sake of the sanity of the user. We get to see the digital oil, water, and trans temps. Some cars only get oil and water.

Maybe check if you can pull the data log for the 4matic system but I wouldn’t know where to start with that. Good luck
 

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I can tell you much more can cause 4matic unavailable. One example is if you have two devices connected through the same Ethernet OBD port, the socket to the ECU gets dropped and the result is an ECU/TCU Module Lost Communication code, and the symptom on screen is '4matic unavailable, do no shift gears, visit dealer' plus limp mode. Car is fine, just reset the socket (clear the DTC) and all is well.

That is just one example, there will absolutely be others that cause 4matic unavailable.

I can't remember the symptom, but if you try to dyno your car without being in dyno mode, the front/rear relative slip causes the car to completely freak out, beyond traction control standards (since that is 'off' [not really off], just like it is 'off' during race start). Could be a 4matic issue until you let off the gas. For a case like that, it would match nicely for this issue a traction problem where more power delivered to the front causes enough slip to make the car upset. Solution would be more traction via tire compound or size or both. But Not clear if that's the issue here.
 

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If the tires' circumference is more than a 3% difference, some things do not work and cause errors. For example, the computer thinks a tire is spinning or on a skid so that it will stop some systems.
 

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Discussion Starter · #7 ·
Thank you all for the suggestions. Yes, the GLA still spins the tires but it launches a lot harder than normal brake boost. The owners manual says overheating gearbox and nothing about tires spinning so I'm wondering if it's that. I still get the message on race start even when I turn traction completely off. I really don't know the main culprit causing this issue. Was anyone in the same situation as me and fixed it?
 

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brake boost, you mean press brake, hit the gas, and lift brake when at 3k RPM?

Do you get that in 2017? In 2015, the drive-by-wire cuts gas when the brake is on. So no heel-toe, revving while braking, etc.

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I don't believe TC is actually off when you turn TC off. Minimal maybe, but not off. I think the nannies are still there at least little bit. At least in 2015. The only mode I am aware of with TC totally off is dyno mode and pretty sure the car won't let me drive on the street in dyno mode.
 

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TC off is not TC off.

In the Nissan 370 (I know, different car, different company, but it is illustrative) you can turn TC totally off, and it is totally on. Those guys figured out the only way to turn it off is to disconnect the yaw sensor in the car, then the ECU throws a code and actually disables traction control.

It would make sense for a similar condition to be present in our vehicles in some capacity, but for 99.9% of us it's a non-issue, and TC-off is good enough. I for one am not going to go off and start experimenting with disconnected sensors to fool TC. Even if TC-off is on enough to put me into a spin on track when I go one wheel off in the dirt.

Again, I'm not saying wheelspin is your root cause here, but if I were in your shoes, it would be my #1 leading hypothesis by a long long shot.
 

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Discussion Starter · #12 ·
brake boost, you mean press brake, hit the gas, and lift brake when at 3k RPM?

Do you get that in 2017? In 2015, the drive-by-wire cuts gas when the brake is on. So no heel-toe, revving while braking, etc.

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I don't believe TC is actually off when you turn TC off. Minimal maybe, but not off. I think the nannies are still there at least little bit.
Yes, hold brake 100%, gas 100% it holds at 3k rpm, and let go of the brake. It doesn't sound like 2-step like race start does.
TC off is not TC off.

In the Nissan 370 (I know, different car, different company, but it is illustrative) you can turn TC totally off, and it is totally on. Those guys figured out the only way to turn it off is to disconnect the yaw sensor in the car, then the ECU throws a code and actually disables traction control.

It would make sense for a similar condition to be present in our vehicles in some capacity, but for 99.9% of us it's a non-issue, and TC-off is good enough. I for one am not going to go off and start experimenting with disconnected sensors to fool TC. Even if TC-off is on enough to put me into a spin on track when I go one wheel off in the dirt.

Again, I'm not saying wheelspin is your root cause here, but if I were in your shoes, it would be my #1 leading hypothesis by a long long shot.
I see where you're going with this but it just doesn't make sense why AMG would completely cut your power off on a drag race launch control, they should expect wheel spin with all that power. If anything it should reduce the power slightly to gain traction then turn the power back up instead of completely cutting the power off. I feel like it's something more serious like the clutch overheating. I will give it a try today when my gearbox temps reach the lowest optimal temp so I can see if it's overheating that's really the issue here. It could be lots of wheel spin like many people are saying but the owners manual says gearbox overheating.
 

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Discussion Starter · #15 ·
What tires are you using?

Does your car have the AMG dynamic plus package, aka factory LSD?
Yes it's fully loaded, all the race stuff. Tires are 245/40/20. One thing I want to mention is that I have a TCU tune but it's not the same company as my eurocharged ECU tune. I called eurocharged and they said that is likely that because the parameters limits are not the same between the ECU and TCU. He also said that the tires should be fine.
 

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Discussion Starter · #18 ·
curious, what brand and model tire are you running.

The brand, the model.
Sure I have the general G-max RS. When I bring the PSI down to 25, they hook super well with very minimal tire spin but the car still ends up saying 4matic currently unavailable at the end of 1st gear on race start. I have a feeling that it's more than just tire spin. I'm starting to believe it's my TCU tune being from a different company than my ECU tune, as the eurocharged guy explained.
 

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Discussion Starter · #20 ·
2nd gear doesn't engage unless I let off the gas them go back into it, that's when power comes back. I think redline is now 6500rpm. I do want to add something to my findings. It's raining heavily today and I just did a brake boost launch (not race start) and tires spun a lot however the car didn't cut off power and instead adjusted itself to get traction back and continued... No 4matic currently unavailable bs. I think it's the transmission tune. Race start on this TCU tune skips the pops in gear upshift and it's instant shifts, whenever it does work, which is almost never. So now I'm convinced that it's the TCU tune not being compatible with my ECU tune.
 
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