I rolled backwards downhill. HELP PLEASE (4 Viewers)

[mantutuli]

*NOTE: questions have been answered, but feel free to comment if your thoughts havent already been expressed


I was on a city street, on what didnt seem like an extremely steep incline(Nashville is pretty darn flat), in fairly heavy traffic.
I was on a side street trying to merge onto a main road, behind a few cars, and I in between taking my foot off the break and putting it quickly onto the gas, the truck rolled backwards a bit, made a horrible grinding-ish type noise, I saw some orange or red warning light flash (i think it was on the tach side), but I quickly put my foot on the brake(within a second or whatever my reaction time was between hearing the noise and hitting the brake), so I couldnt really tell what the light was, as it went away as soon as I stopped rolling.

This has never happened to me with any vehicle I've ever owned. The only time I've ever rolled backwards a little down a hill was in a truck with a manual trans, but that was when I was practicing/learning how to not roll backwards down a hill while driving a stick.

It happened 2 or 3 times as I wasnt sure what/how I should handle it, and frankly, I was freaked out it was happening, so I was a little panicked.

A few questions
1) Has this happened to anyone?
2) "Should" this have happened? I would have thought the trucks trans/rear/engine should have had enough strength, torque, etc whatever to prevent it from rolling backwards with the engine running and in gear.
3) What potential damage could have occurred?
4) Anyone know what the warning light might have been? Check the OBDII reader, it didnt show any codes, but I dont know if it shows trans issues. I have the OBDLink mx+
4) I have a Luxury sport trim, so no crawl mode. What's the correct action to take in the future should i find myself stopped on some grade? Lock the Diff? Put it in low 4? Combination of things?


Thanks in advance

 

[Poop Bubbles]

LOL Its just your traction control. You're overthinking it.

 

[mantutuli]

LOL Its just your traction control. You're overthinking it.

So turn off traction control?
The noise was "nothing" ?

 

[vipergrhd]

LOL Its just your traction control. You're overthinking it.

You beat me to it. Was the road slippery? @mantutuli

 

[vipergrhd]

So turn off traction control?
The noise was "nothing" ?

The noise is your ABS trying to stop the spinning tires, it's pulsing the brakes on the slipping tires.

 

[mantutuli]

You beat me to it. Was the road slippery? @mantutuli

Not at all

 

[mantutuli]

The noise is your ABS trying to stop the spinning tires, it's pulsing the brakes on the slipping tires.

thank you!!!
Should I turn off the traction control in similar situations, or just dont event sweat it, because its doing its job?

 

[vipergrhd]

Does your GX have a Hill assist feature? @mantutuli
Is it on or off?

 

[mantutuli]

Does your GX have a Hill assist feature? @mantutuli
Is it on or off?

DAC was off. I've only ever used it actually going down a dirt road on a steep hill. Does it work going up a hill to?

 

[vipergrhd]

DAC was off. I've only ever used it actually going down a dirt road on a steep hill. Does it work going up a hill to?

It's the opposite of DAC which is a great feature going down hill, it basically holds the brakes for a few seconds on steep incline so you could switch your foot to the gas pedal.

 

[WTITW]

I would recommend leaving traction control on. The noise was just your brakes pulsing. The gx has alarmingly noisey and crunchy abs for the uninitiated.

 

[mantutuli]

DAC was off. I've only ever used it actually going down a dirt road on a steep hill.

It's the opposite of DAC which is a great feature going down hill, it basically holds the brakes for a few seconds on steep incline so you could switch your foot to the gas pedal.

thanks. Dont have the up hill in mine. Only DAC

 

[mantutuli]

I would recommend leaving traction control on. The noise was just your brakes pulsing. The gx has alarmingly noisey and crunchy abs for the uninitiated.

Thanks

 

[mantutuli]

thank you all who responded. took a great weight off my mind

 

[Roody]

Yeah, definitely not something to worry about. Mine does that on steeper city streets when the weight unloads and the tires are trying for grip that they have, but that the sensors haven't entirely understood as being slightly different from what they had milliseconds ago.

The only questions I'd ask are, what year GX and what condition (alluding to maybe the ABS sensors which aid in traction control are tired, corroded, and/or needing to be replaced), and what are the condition of your tires?

 

[jeremy j]

Just to add my experience.

My driveway is pretty steep so when I back out of my garage I sometimes roll backward a little before getting on the gas and it makes all these noises and I see the TC lights flashing. I've never had a vehicle act like that either but it is normal for a GX.

 

[r2m]

It's the opposite of DAC which is a great feature going down hill, it basically holds the brakes for a few seconds on steep incline so you could switch your foot to the gas pedal.

Generally, I've found using DAC allows my rig to descend too fast even when in 4Lo, which causes me to still have to tap the brakes.
I really need/want Crawl Control. (already have MT )
But to the original post's, yeah, DAC and traction control does make quite a ruckus when it gets activated, and one would think something is breaking.

 

[vipergrhd]

thanks. Dont have the up hill in mine. Only DAC

Just to add my experience.

My driveway is pretty steep so when I back out of my garage I sometimes roll backward a little before getting on the gas and it makes all these noises and I see the TC lights flashing. I've never had a vehicle act like that either but it is normal for a GX.

I'm surprised that Lexus don't have a hill assist feature, I would rather have that than the DAC.

 

[23GXOR]

Rolling backwards on an incline when you let off the brake is perfectly normal behavior for this platform, IIRC it's even mentioned in the owners manual. It certainly is disconcerting the first time it happens, especially when the braking system designed to arrest your movement kicks in and makes a ton of ABS racket.

I think the tall profile of the GX makes it feel worse than it really is. I've never measured it, but the truck seems to stop rolling within a foot or so. As for why this is a unique issue to the GX I'm sure it has something to do with the full time 4WD system.

The only electronic system involved in any of this is ABS. DAC, TRAC, VSC, have nothing to do with it. It's just your ABS system activating to clamp down on the brakes and prevent a roll from turning in to a skid, as described in your owners manual as the 'hill-start assist control' system. In my manual the section that describes how this functions is on page 371, might be different for yours.

I don't think the earlier years of GX had a hill-start system, which may explain some confusion on the topic.

 

[Acrad]

Sounds like Hill Start Assist Control and is listed on all brochures and manuals since 2010 model year

FSM says---> Hill-start Assist Control: When the vehicle starts off on a steep hill, hill-start assist control detects the backward descent of the vehicle and performs 4-wheel hydraulic pressure control to reduce the speed of the vehicle.

• Depressing the brake pedal cancels control of the hill-start assist control system.
• The system does not operate when the shift lever is in P or N, or when the vehicle is being driven/rolling back up a slope with the shift lever in R.

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