I have a 2001 Durango with the 4.7 and 4x4 and my g/f was driving it home and had to slam on the brakes for a sudden traffic jam. All 4 wheels locked up on it and she had to do a emergency lane change to avoid a accident. Though a week earlier we took it out in the snow and locked all 4 on a slight decline to a stop with ice on the road and thought nothing of it because the speed was slow enough to possibly not trigger the ABS.

Now that she is a bit scared to drive it I need to find a fix for this issue. I ran the scanner on it today and there are no codes that flag with the vehicle though one thing that did surprise me was the VSS was showing 18mph in park when i ran the diagnostics.

I am thinking this could be a rear diff speed sensor based on everything i have seen thru looking thru the forums on durangos.

 

That's impossible. These speed sensor works off Rotation of a Magnet and a pick up coil. If they fail, they would read 0mph at all time.
I think you should verify if the ABS kicks in at all when u need it by slamming the brake few times before you pull your hair out chasing ghost.

Or maybe it is just your girlfriend want to buy a new car? hint hint
Ask her if she likes the 2012 Durango, hehe...

ABS doesn't shorten stopping distance, it only prevents Vehicle goes Side way when you slam the brake and also trying to turn. If car goes straight even when all wheel locks up, ABS might not kick in.
Wethere if ABS kicks in or not, if you are going to fast, you will still rear end the car in front of you.

 

I agree with steak, I very highly doubt that a bad sensor would be showing 18mph when stopped. I suppose that maybe there could be a one in a million chance that an intermittent short is causing this, but at the same time the cel would be on and there would be codes. Are you sure your durango has 4 wheel abs. They came standard with rear wheel abs (since the back end is lighter and would lock up first), but to get front abs too was a $400 option.

ABS is designed to keep the wheels rotating during an emergency stop to allow the driver to steer/keep control of the vehicle. And it will kick in even if the car is turning. The abs system compares the speeds of the different wheels/axles and if one is lower is decreases the amount of braking force to that wheel. And now for a short physics lesson. Tires have a property called peak grip. This is the most grip they can possibly make for any given road condition. Peak grip occurs an instant before the wheels lock. Coincidentally when the ABS is keeping the wheels rotating it also is keeping the wheels closer to their peak grip. Once the wheels lock they are below the peak grip. Now while it is true that this makes a car stop shorter it will only be an inch or two and no more, unless of course you're going 200mph in a super car which a durango isn't.

In snow, mud, ice, etc. abs will actually increase stopping distances because when the wheels lock in these conditions they can actually dig down into the snow or whatever and have a higher surface area contributing to the stopping. (more surface area = more stopping force) If the abs keeps the wheels rotating on these surfaces (which some abs systems can't do) there will be less surface area contributing to the stopping.

What i'd do if i were you is go out to an empty parking lot or somewhere away from other cars and slam on the brakes while going about 20mph. Get out and check to see which wheels left skidmarks, if any, and which didn't. If the back left none and the front did most likely you just have rear abs, and are fine. If all 4 don't leave skidmarks you have 4 wheel abs and are fine. If they all lock up something isn't right. As I said before I suppose it could be possible that your speed sensors need replaced, but I doubt it.

 

ok thanks a lot that_guy, you posted most of what i was going to say

however i suggest either getting a build sheet from the dealer(have your VIN handy) to see if you have 4 wheel ABS or rwabs only, or pull the front tires off and look for the abs sensors in the hub (the wires hanging out of the hub will be a dead give away)

if you have rear whele ABS only chances are that you will not feel the pedal shake when it goes off and will not hear anything special either, IME if you are going too slow (iv locked up all 4 of my tires from just over 20mph) the ABS is simply ignored(i have 4 wheel ABS). that said IMO you have the better problem of two that can pop up with ABS, oversensitive or undersensitive, yours is under and that is preferable to me in 95% of driving conditions. Mine is oversensitive, i have felt it go off on the highway when traffic stops quickly (even just slowing down too fast).

When ABS goes off what it does is it is pumping the brakes for you, this is done to 'unlock' (really trying to keep the wheels from locking up) the brakes, in reality it lock and unlocks the brakes many times in a very short period of time. This increases your stopping distance over a good driver who knows how to modulate the breaks to maintain your peak stopping performance (a brake force applied which is just barely shy of lock up force). If you learn how to drive w/o ABS you will learn very quickly that it is not good in many conditions for this very reason. that being said, it most certainly does have its place since there are too many people who dont have the ability to properly modulate the brakes, or to keep a cool enough head in these panic situations to do this properly, it will eventually become instinct, but until then . . .



on the speed sensor reading 18MPH, yes that would be the rear wheel speed sensor, if it is dirty or broken it could read anything it wants to, unplug it from the rear differential and see what it claims to read, if the reading goes to 0 replace the sensor. (it seems odd that it would read a speed when you are not moving, but electronics will do what they want regardless of what we want to think they will)

 

+1 on the electronics shrp