Reduced Braking Performance Scare

[303ChickenMan]

I had a scary issue in my Gren today. I drove up to 12,000 feet looking for elk on a very rugged 4x4 shelf trail. On the way back down, I got a “Reduced Braking Performance” and a red brake error light in one of the worst possible spots.

To keep it short, the trail was icy and I had already had a bad scare, so I tried the Downhill Assist in a tight snowy corner. The pitch and roll were simultaneously very steep (probably 20-25 degrees down and side-to-side). Before I engaged the DA, I stopped with my foot firmly on the brake… and it didn’t feel right. I successfully engaged DA and got out of the precarious spot in a very low gear. Simultaneously I got the “Reduced Braking Performance” screen message in red and had the red brake system warning light on the dash.

The brake pedal could go all the way to the floor, it had some resistance, but would click as it engaged. I could also feel the click in the pedal.

I did what any responsible Grenadier owner would do! I turned it off for a few minutes until the center screen turned off and turned it back on and checked my brake fluid, which was full. I got one more funky press out of the pedal that then returned to normal and my warnings went away. I successfully drove the rest of the day and was unable to recreate the issue.

Was I scared? I won’t admit it. Should I have been? Yes. I had a long ways to go on that gnarly trail.

Can anyone explain what happened to my braking system?

 

[Tazzieman]

Brake sensor wire/ connection is one guess.

 

[rob88]

Your brakes overheated from the long descent. The fluid boiled, creating air bubbles that made the pedal go soft. The click was likely the ABS system. Letting it cool fixed the issue. Use low gears and downhill assist earlier to prevent it.

 

[303ChickenMan]

Your brakes overheated from the long descent. The fluid boiled, creating air bubbles that made the pedal go soft. The click was likely the ABS system. Letting it cool fixed the issue. Use low gears and downhill assist earlier to prevent it.

I hope that’s the case! It’s within the realm of possibilities. However, I had only descended about 1000 feet and rode gears 2-3 in low range coming down. Who knows.

 

[Tazzieman]

I hope that’s the case! It’s within the realm of possibilities. However, I had only descended about 1000 feet and rode gears 2-3 in low range coming down. Who knows.

Go up again and see if happens the second time!

 

[Brad@SuperiorCO]

I agree with @rob88 . This summer coming off a 13,000 ft pass, the Gren in front of me was on his brakes a lot, they over heated and he had the same warning. Good to be warned before they fail. What trail were you on? I would like to get out again next week, but I worry there is too much ice. Glad you made it back safely.

 

[Shopkeep]

Fluid boils at lower temp at higher altitudes?

 

[303ChickenMan]

I agree with @rob88 . This summer coming off a 13,000 ft pass, the Gren in front of me was on his brakes a lot, they over heated and he had the same warning. Good to be warned before they fail. What trail were you on? I would like to get out again next week, but I worry there is too much ice. Glad you made it back safely.

That confirms Rob88’s suspicion! Makes sense. It’s easy to forget how heavy these things are. I was on Deer Creek trail coming up from Montezuma. It’s on the other side of Radical Hill and Webster Pass. No elk up there!

It’s pretty sketchy right now. There’s a few slabs of ice on the shelf road that make it very puckery. Snow isn’t too deep yet, though.

Fluid boils at lower temp at higher altitudes?

Yes! For example, water boils at 189 degrees (87c) at the 12,000 ft elevation I was at today. I’m sure the same is true for brake fluid.

Thanks, guys! Lesson learned.

 

[NQ94]

If the brake fluid has heated to the point of losing pedal feel and getting vapour in the system it's probably a good idea to have the fluid flushed and replaced.

 

[Tazzieman]

If the brake fluid has heated to the point of losing pedal feel and getting vapour in the system it's probably a good idea to have the fluid flushed and replaced.

Racing fluid worthwhile? Compatible?

 

[AWo]

Your brakes overheated from the long descent. The fluid boiled, creating air bubbles that made the pedal go soft. The click was likely the ABS system. Letting it cool fixed the issue. Use low gears and downhill assist earlier to prevent it.

The downhill assist uses the brakes as well. I never had to use a DA on icy roads, but if the brake system heats up, that could also happen with the DA, as it also uses the brakes. Maybe you need to take other measures, as the DA is not designated to go down icy tracks.

Maybe it would be better to use snow chains and winter tires (if not already done) or tire spikes. Every system has its limit and a steep, icy track may be over the limit of every system.

AWo

 

[NQ94]

Racing fluid worthwhile? Compatible?

Might have to check. DOT 5, 5.1 are not compatible with Dot 4 and 3 brake fluids.

 

[landmannnn]

The other factor to consider is the moisture content in brake fluid.
At 12000 ft water will boil at 90C or 190F.
Normally brake fluid should be changed every 2 years or 24k miles.
Off road use, especially in damp conditions, much more frequently.

 

[MattA]

Use a lower gear and never ride the brakes on a long down hill stretch
Number 1 rule when off roading