[purohitanuj]

Just returned from an Umlingla trip with the SimplyJimny group (with 10 Jimny's) and I need to share some crucial findings with a timeline.

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), I grew concerned. I asked Manik to give it a try, and he too was taken aback by the brakes, remarking, 'It feels like trying to tow a dead car.'

I attempted to force the brake pedal down with full strength while in neutral, revving the engine ( The brake pedal moved in much further on revving) . Finally, I got some braking action. The parking brake, however, functioned normally.

Concerned about my Jimny, we decided to address the brake issue and have them checked and bled in Leh. I was instructed to trail the convoy.

Upon reaching Shinkula top, I realized my brakes were non-existent! I ceased using the parking brake and once again revved the engine to regain some braking power. Additionally, I observed the ABS motor engaging when I lightly rested my foot on the brake pedal without applying pressure.

This same issue recurred with all Jimnys over the next couple of days. I encountered numerous local Jimny owners who experienced identical problems on this trip.

After some driving and analysis, here's my assessment:

At high altitudes, the brake booster fails to generate sufficient boost for the brake system at idling or lower RPMs.
This is particularly critical in AT mode, as in 'D' mode, when the car descends a slope, the AT shifts to the highest gear ( or coasts) , causing a drop in RPMs akin to idle conditions. Within this RPM range, the brake booster struggles to provide adequate boost. This predicament arises when attempting to brake for a hairpin bend, leaving little time for corrective action.

Hence, I strongly implore Maruti Suzuki to conduct thorough testing on high-altitude passes and address this issue. I personally experienced two near misses due to this very problem.

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.

It appears that the very purpose of owning a Jimny is being undermined. Brakes failing and 4x4 hubs refusing to lock in high-altitude regions present a life-threatening issue. I fervently urge Maruti Suzuki to address these concerns before any lives are put in jeopardy.

[sadnabrina]

Originally Posted by purohitanuj

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.

In MT while idling -
Did anyone try brake feel while idling?
Did they face front air locker failure while idling?

By the way, while on a descent, shouldn't the AT be always kept at 2 or L (depending on gradient) for engine braking?

[purohitanuj]

Originally Posted by sadnabrina

In MT while idling -
Did anyone try brake feel while idling?
Did they face front air locker failure while idling?

By the way, while on a descent, shouldn't the AT be always kept at 2 or L (depending on gradient) for engine braking?

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.

[sadnabrina]

Originally Posted by purohitanuj

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.

Absolutely agree that this is a very very serious issue and MSIL needs to fix it asap

I have faced a dual brake hose failure on a downwards slope on a fully loaded (with your most near and dear ones on board) Mahindra. So I know how it feels when your brakes are non existant.

[subbu567]

Originally Posted by purohitanuj

It appears that the very purpose of owning a Jimny is being undermined. Brakes failing and 4x4 hubs refusing to lock in high-altitude regions present a life-threatening issue. I fervently urge Maruti Suzuki to address these concerns before any lives are put in jeopardy.

This is a serious issue. Thanks for bringing this up and potentially helping us to avoid any such mishap. We should collectively write to Maruti for recall/replacements/repairs. Maruti may probably claim you are supposed to drive at L or 2 anyway in such situations I am speculating. Have you, or anyone from your group raised this issue with Maruti?

[bobbyblr]

Originally Posted by purohitanuj

At high altitudes, the brake booster fails to generate sufficient boost for the brake system at idling or lower RPMs.

Does Jimny has any sensor to measure the Vacuum generated from the engine that is supplied to the Brake booster? If yes, then should this sensor give the ECU the error message and the dashboard brake light should get ON or something ?

Or may be one should add an external Vacuum Gauge like below on the dashboard:
https://www.amazon.in/ESUPPORT-Turbo...00SMDR3Z2?th=1

[Kosfactor]

Originally Posted by purohitanuj

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.

As per the owners manual it advices one to drive down slopes in 2\L mode rather than D, I think this AT does not grade shift according to slope so that is something to keep in mind. Also asks the driver to press the brake pedal as hard as one can when the brake vacuum is not there , they are certainly aware of the issue with brakes as well as the hubs but the owner`s manual is not entirely clear in it`s directions. It would certainly add to the cost and maybe a bit of fuel mileage to add a vacuum pump.

Truth be told, unless you drive an old M800 or some old Jeep, your right foot can never apply that sort of pressure in normal driving conditions, left foot certainly can apply a lot of pressure if you have driven manual cars but the right foot is much more pampered.

[Aditya]

Maruti Jimny AT | Brakes not functioning at low rpm at high altitudes - Posts moved to a new thread.

[quickdraw]

I've recently spent decent time with my Jimny in high altitude passes, but only faced a similar problem once. The brake pedal became rock hard and brakes stopped working. I noticed that the auto engine start stop was enabled. Disabled that and switched car off and on and it did not reoccur.

Regarding the 4H not engaging I maybe only had the car reluctant to do that once, but a quick up and down of the 4x4 lever sorted it out and didn't think much of it.

[raptor_diwan]

This is a significant concern, and one can only hope that they address it promptly. It's surprising that they overlooked it, especially considering that in India, testing cars usually involves multiple drives on the Ladakh circuit.

[itwasntme]

Is this issue similar to the infamous Swift matter many years back?

https://www.team-bhp.com/forum/road-...ake-issue.html (Attention: New Maruti Suzuki Swift Brake Issue)

[purohitanuj]

Originally Posted by raptor_diwan

This is a significant concern, and one can only hope that they address it promptly. It's surprising that they overlooked it, especially considering that in India, testing cars usually involves multiple drives on the Ladakh circuit.

I guess that’s because the test drivers are generally ripping out the cars which keeps the engine RPMs really high. Try a sedative profile on down slope in “D” and you will be shocked by a surprise! Keeping engine revs above 2K is the current solution.

Originally Posted by quickdraw

I've recently spent decent time with my Jimny in high altitude passes, but only faced a similar problem once. The brake pedal became rock hard and brakes stopped working. I noticed that the auto engine start stop was enabled. Disabled that and switched car off and on and it did not reoccur.

Regarding the 4H not engaging I maybe only had the car reluctant to do that once, but a quick up and down of the 4x4 lever sorted it out and didn't think much of it.

Can you please list the altitude of the pass(es)?
My first action after starting Jimny is to disable the A.S.S. Function.

[Venkat_KM]

This is a serious issue to be addressed. You have mentioned in your post that there is some braking action after revving the engine at high RPMs, this means the brake booster is not getting sufficient vaccum for its proper functioning. In any mordern car system, vacuum line for the brake booster will be given full priority with non return valves and also a small tank to aid the system.
I would suggest you to check for any leakage in the vacuum lines, which might be the reason for the same.

Since you have not mentioned about any problems in other Gymnys from your trip, I assume other vehicles just did fine. So might not be a common issue and rather a QC/mechanical issue?

[purohitanuj]

Originally Posted by Venkat_KM

This is a serious issue to be addressed. You have mentioned in your post that there is some braking action after revving the engine at high RPMs, this means the brake booster is not getting sufficient vaccum for its proper functioning. In any mordern car system, vacuum line for the brake booster will be given full priority with non return valves and also a small tank to aid the system.
I would suggest you to check for any leakage in the vacuum lines, which might be the reason for the same.

Since you have not mentioned about any problems in other Gymnys from your trip, I assume other vehicles just did fine. So might not be a common issue and rather a QC/mechanical issue?

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.

[Jeroen]

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 can’t 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