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Funny ABS experience on a slippery surface
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=28197		 Page 1 of 1
Author:  Uffe [ Fri Jan 04, 2008 3:11 pm ]
Post subject:  Funny ABS experience on a slippery surface
Hi guys.

Recently we got a little tiny bit of snow, unfortunatly not enough to go out and play with the Jeep. Near my home (less than 50 meters actually) there is a little slope. On this slope there is noone who is taking care of salting or scraping the snow off the road, so we got the road tightly packed with compressed snow.

So this little slope presented me with my inner child. How about stopping the Jeep in the steepest point and try to make wheelspin in RWD?? Great idea, I thought!

So I drove about half-way up the slope and pressed the brake. To my great disappointment the idle torque of the engine was able to get the car rolling ever so slowly. Fortunatly to my great pleasure when I tapped the speeder the wheels spun like crazy. So I did a little of wheel-spinning and got bored with it real fast. I pressed the brake and wanted to go into full-time (to get up the slope which was slippery enough to get me stuck on it :D). Put the transmission in neutral and shifted to full-time, and rolled the car slowly backwards. Engaged drive on the transmission and I got up no problems.

When I got back home I noticed the ABS light was shining and the (O! BRAKE) light was up too. I thought that was odd, I had no traction control or anything. Why would ABS be affected by me spinning my rear wheels? I tried the brakes and they work fine. The ABS doesn't cut in at really low speed (ice covered road in front of my apartment) but brakes definatly worked fine. Tried going back and forth but the lights stayed on.

When I drove to town to buy some presents (checked brake fluid and looked at the brake discs and calipers before I left, obviously!) and got to dry tarmac the lights both went off and haven't shown up again.

When I got back I spun the tyres again. ... and again when I got "stuck" on the slope :D No lights came up. I tried tapping the brake and quickly the speeder to try and get the ABS system confused again, to no avail. Went to pick up the girlfriend and on the way back I spun the wheels for the 3rd time in a stuck position.

Anyone got any ideas why the ABS light came on along with the brake lights?? I have noticed the ABS light staying on for a little longer than normal, but after my little adventure and cure for the ABS light it has returned to normal again.
Author:  vtdog [ Fri Jan 04, 2008 5:02 pm ]
Post subject: 
A few years agi I had a similar problem with ABS/Brake light coming on after spinning wheels while trying to get up a very icy driveway. The lights reset after turning off the car and I have never had the ABS lights come on again except during system check when starting. If I remember right, the problem was diagnosed here as a wheel spin sensor looking at the different rotations of the tires based on the slippage.
Author:  Uffe [ Fri Jan 04, 2008 5:58 pm ]
Post subject: 
Odd part is that I had turned off the car with no effect, ABS light came on, went off, and stayed on until it went away as described when I reached dry tarmac.

Your description sounds correct to me. This is what I theorized myself but I was afraid I might be misleading myself so I wanted a second opinion. Thanks! :)
Author:  Scott Langohr [ Fri Jan 04, 2008 6:01 pm ]
Post subject:  ABS Light
It happened to me in my drive two nights ago. Drove in normally but, while backing up to back into the garage, I got hung in a drift where the anti-spin rear differential could not get me through. I shifted into part time while still in reverse but stopped. It came out easily but both lights came on. I parked in the garage and shifted into park and 2WD and stoped the engine. I turned it back on after a few seconds to see if it would reset. The red light went out but the ABS remained. I shut it back off and plugged the engine heater and left it until the next morning. When I fired it up, the ABS still remained on. The brakes seamd to work fine so I headed to work. About 50 yards out on the dry pavement and the ABS light went out. Not been a problen since and the braking system has worked on icey parking lots a couple of times. Must have been a quirky sequence that caused it.
Author:  CATCRD [ Fri Jan 04, 2008 7:44 pm ]
Post subject: 
This is typical when getting lots of wheelspin. The computer gets all kinds of conflicting data from wheel speed sensors and thinks there is a system fault. It'll reset itself.
Author:  GilaMonster [ Fri Jan 04, 2008 11:12 pm ]
Post subject:  Unrelated instance, but may be the answer
We have to perform rolling emission tests here in AZ, and on some of my ABS cars the ABS light will illuminate after one of these tests. The test is to roll your drive wheels onto rollers (much like a dyno test) and proceed to drive at predetermined speeds for exhaust readings. The inconsistency of having one set of wheels rolling (front or rear drive wheels) while the other is stationary will "trip out" the ABS brain. It resets after a complete restart of the ignition system. Funny, I have no idea what they do for a subaru that is AWD, or an audi for that matter.

Anyway, it could be that you succeeded in getting a higher wheel speed on the rear with the spin-out you wanted and it "tripped out" your ABS computer since the front wheels were not moving at any speed relative to the rear.
Author:  Uffe [ Sat Jan 05, 2008 5:58 am ]
Post subject: 
Thanks guys! Good information right there :)

I will proceed as normal, at WOT! :D
Author:  dgeist [ Sat Jan 05, 2008 12:09 pm ]
Post subject:  Re: Unrelated instance, but may be the answer
GilaMonster wrote:
Funny, I have no idea what they do for a subaru that is AWD, or an audi for that matter.



Georgia has the same system. When you pull up in a quattro (like my wife's), they put the vin in the computer, roll you onto the rollers, put the plug on your ODB2 connected and just never put it in gear. The guy that did the test recently called it the "all-wheel-drive non-disengageable" exemption. I'm guessing LR Defenders are the same way :)
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