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Old 26th September 2023, 11:50   #16
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

Quote:
Originally Posted by purohitanuj View Post
Can you please list the altitude of the pass(es)?
My first action after starting Jimny is to disable the A.S.S. Function.
Certainly, I was in the 12000-15000ft range mostly.
  • Kumzum - 15000ft
  • Pin Valley - ~12000ft
  • Chichum - 13600ft
  • Hikkim - 14440ft
  • Komic - 15049ft
  • Kaza - 12000ft
  • Nako - 12000ft

I do disable the ASS function always in this incident I saw it was on and causing the engine to cut off. Thought this might be causing some brake booster issue so decided to switch the engine off and on again.
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Old 26th September 2023, 11:53   #17
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

I just searched for the word "Vacuum" in the Jimny owners manual and found that there could a sensor to monitor the Brake Booster Vacuum as the ASS (Auto Start Stop) will only stop the engine if the Brake booster vacuum pressure is normal.

Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes-jimnybrakeboosteriss.png

Also in the owners manual there is a mention on how to drive the vehicle on a Long Down-hill Slope for both MT & AT using engine braking.

For manual transmission vehicle, shift down to a lower gear one by one.
Name:  JimnySlopeMT.PNG
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For automatic transmission vehicle, turn off the overdrive (O/D) switch or shift the gearshift lever into 2 or L.
Name:  JimnySlopeAT.PNG
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Old 26th September 2023, 12:04   #18
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

It's bad enough that Maruti Suzuki cheaps out on metal quality and structural integrity when making cars. Looks like the lack of any consequences has emboldened them to cheap out on brakes too. Does anyone know if this is a common issue on International spec Jimnys as well or limited to India?
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Old 26th September 2023, 12:29   #19
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Quote:
Originally Posted by Jeroen View Post
Without the booster the brakes should still work. You just need to press the brake pedal harder. If the brakes were not functioning at all, there is something else wrong.

The problem with vacuum boost loosing some of its efficiency at high altitude is well known.
However, it is NA engines that are most prone to it, as they never have separate vacuum pumps.

I remember taking my Jeep Cherokee up into the Rocky Mountains all the way to about 11-12000 feet. The Cherokee has a NA engine. Although I cant recall any real issues with the brakes, we did get issues with the climate control. The little valves on it are also vacuum controlled. The vacuum was too low for it to work properly.

Jeroen
The brakes do work but one has to push really hard. On any hairpin bend, this could be a very tricky condition when you suddenly spot incoming traffic and would like to stop instantly. I have a video of me trying to stop once I spot trucks coming in and the Jimny did stop with almost zero margin left.



Please see if you can judge the issue here. I was driving in D mode and in a relaxed manner.

Last edited by graaja : 27th September 2023 at 05:16. Reason: Merging back to back posts for continuity
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Old 26th September 2023, 12:42   #20
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by purohitanuj View Post
Just returned from an Umlingla trip

During my stop in Jispa, I attempted to move my Jimny (Alpha AT) the next morning, but was met with a startling discovery: Zero braking! The brake pedal felt rock solid and wouldn't budge. After checking the brake fluid (which was at proper levels)

The parking brake, however, functioned normally.
This is something really serious.

Hear me out from the limited knowledge I have regarding the fluids. Since brake fluid is hygroscopic (the main enemy), it must have absorbed the moisture during the drive and while the car was stopped overnight (I assume near freezing temperature) would have frozen the moisture in the fluid and made this brake fluid thicker with high viscosity, which the break booster pump cannot handle (initially during start-up) or will have a limited capability to transfer fluid/pressure for slave cylinder to act and have the required bite.

Till the temperature of the fluid is increased while pumping of the breaks during driving and evaporating the moisture from the brake fluid. Then the brake system works normally. Hence you were able to get some bite out of your breaks. Did your ABS mal functioned? or light popped up, then definitely it's due to the viscosity of the brake fluid (with excessive moisture) then.

It happened for other cars too, I would say it has to do with Tempretature/Altitude/Dew point/Pressure, as all are somewhat dependent on each other.

Since your "parking brakes" were functioning normally makes my assumptions more robust, because these are completely mechanical and use only cables and levers to operate. These Have nothing to do with temperature or pressure/Altitude.


I would suggest you to change the brake fluid (also get the break fluid checked for any moisture content) and while driving down steep slopes for long distances, go in for manual mode. This visual warning boards (change to manual), I have seen at many European mountain drives just before the steep slopes begin, probably such warning signs are missing in India due to not much AT's on the roads.

This would be an eye opener for people who want to drive in winter conditions to check/change/replace thier brake fuilds well in advance to avoid the re-occurence of such dangerous conditions.

Quote:
Originally Posted by purohitanuj View Post
Felt like ABS is confused.
Viscosity of the brake fluid is the most important factor for ABS, ESP to function safely and reliably, the brake fluid must be able to penetrate the systems hydraulic units (Pipes/Pumps) in fractions of a second. That's why I have mentioned the presence of mositure in the break fluid and you have felt the ABS to be confused.

Cheers

Last edited by Aditya : 26th September 2023 at 19:45. Reason: As requested
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Old 26th September 2023, 12:49   #21
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

This is an old issue with Maruti.

I had faced the same with my 2014 Ritz Zxi If I was coasting down a flyover in higher gear, the brakes stopped working and became hard. Only when I pressed the clutch and revved the engine that the brakes went back to normal.

Maruti flew down someone from the factory and they did a software update and it was sorted. I think there was a thread as well on something similar occurring in a swift. This was way back in 2015-2016. Surprised that it is still happening.
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Old 26th September 2023, 12:52   #22
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by NomadSK View Post
This is something really serious.

Hear me out from the limited knowledge I.. Did your ABS mal functioned? ..
The ABS motor did kick twice ( on different days ) when I just touched the brakes ( didn't press a bit; just touched) . The road condition was clear with no reason for ABS to kick in. It went away in 1-2 seconds. Felt like ABS is confused. It happened at very low speeds, below 20 km/hr for sure. Dont know what ever that means, but it could help people analyzing the issue.
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Old 26th September 2023, 13:15   #23
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Re: Maruti Jimny Review

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Originally Posted by purohitanuj View Post
We didn't had any MTs in our group. You are right that AT should be kept in L or 2; but it does not mean that you have to entirely rely on engine braking. Normal brakes should be working. I know what brake fading feels like and conditions leading to it. In this case, it was not fading. The brake pedal just dint move.
This post is a potential lifesaver for Jimny AT owners. How long does the driver have to react if one faces such an issue on a turn at higher altitudes? This is a tragedy waiting to happen.

As Maruti seems to know the issue, they ought to address this right away + list this fact in red inside the vehicle, mentioning the height above which Jimny L/2 ought to be engaged for safety reasons.
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Old 26th September 2023, 13:36   #24
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Re: Maruti Jimny Review

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Originally Posted by RDS View Post
This post is a potential lifesaver for Jimny AT owners. How long does the driver have to react if one faces such an issue on a turn at higher altitudes? This is a tragedy waiting to happen.

As Maruti seems to know the issue, they ought to address this right away + list this fact in red inside the vehicle, mentioning the height above which Jimny L/2 ought to be engaged for safety reasons.
It will catch you off guard. As of now, please try to maintain good rpms being in L or 2.
We all were brake checking after few minutes. If the brakes got consistent feeling ( even if its bad braking ), then the driver will condition himself. However it works some time with great bite and then sometime no bite is scary.
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Old 26th September 2023, 13:44   #25
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by purohitanuj View Post
The brakes do work but one has to push really hard..
We are so used to having power assist brakes very few of us have a feeling for how hard you need to push a brake without power assist.

If you ever had your car towed you would experience the same! Very unsettling if you are not used to it.

Jeroen
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Old 26th September 2023, 14:15   #26
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes


Similar problem reported here as well - from 21:30 time.
This is MT variant.

Last edited by purohitanuj : 26th September 2023 at 14:21.
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Old 26th September 2023, 14:24   #27
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by purohitanuj View Post
I did mention in my post that similar issue / under braking was observed in allmost all Jimnys and even I met few other Jimnys on the way and they also claimed noticeable less braking on those terrains.
I think its mostly observed by ones who keep the AT in "D" mode.
My other car is Scorpio S10 AT and it does sense incline / decline (DSI gearbox) and it does keep the RPMs high even in D mode.
This is a serious concern. Is this something that you observed even at 4-4.5k metres altitude as well? I did those altitudes on Spiti trip in 6AT XL6 and never experienced such thing. 6AT does not have any L/2 mode but it always detect the slope and maintain the gear which keeps the rpm close to 2k rpm. Was Jimny climbing to higher gears while descending in D mode?

Last edited by saurabh041086 : 26th September 2023 at 14:29.
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Old 26th September 2023, 14:36   #28
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by saurabh041086 View Post
This is a serious concern. Is this something that you observed even at 4-4.5k metres altitude as well? I did those altitudes on Spiti trip in 6AT XL6 and never experienced such thing. 6AT does not have any L/2 mode but it always detect the slope and maintain the gear which keeps the rpm close to 2k rpm. Was Jimny climbing to higher gears while descending in D mode?
Jimny would put in 4th gear as soon as it descends. One has to manually keep the gear box in L or 2 for engine braking. Jispa is around 3200 mts when I first encountered this issue.
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Old 26th September 2023, 16:23   #29
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by purohitanuj View Post

Following my analysis, everyone opted to drive in either 'L' or '2' to maintain higher engine revs throughout the trip. Upon returning to lower altitudes, the problem vanished as if it never occurred. In a manual transmission, one typically operates in a lower gear, resulting in higher engine RPMs. Consequently, this issue is either non-existent or not as severe.

Furthermore, at higher altitudes, 4H/L struggles to engage the front hubs (vacuum assisted), with the 4x4 indicator continuously blinking. To circumvent this, I shifted the car into neutral in 2H and revved the engine to 3K from idle and then back to idle. While repeating this process, I pulled the transfer case lever back for 4H, and it locked within 1-2 seconds (solid green light). Once engaged, it remained locked regardless of engine RPMs. Some of us took shortcuts and nearly all managed on 2L as the hubs failed to lock, but the transfer case shifted into crawl ratio.
Thank you very much for highlighting this. For AT vehicles did both the problem go away/reduce after shifting to L or 2? I have to visit my relatives very soon and they live in higher altitudes of Himachal so was hoping to be prepared before venturing out.
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Old 26th September 2023, 16:36   #30
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Re: Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes

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Originally Posted by sammysossa View Post
Thank you very much for highlighting this. For AT vehicles did both the problem go away/reduce after shifting to L or 2? I have to visit my relatives very soon and they live in higher altitudes of Himachal so was hoping to be prepared before venturing out.
Yes, the issue reduces once you drive in 2 or L; but it is still noticeable. Please pay attention to changes in the behavior of the brakes and it should be fine. My best wishes for your trip!
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