I guess we're all familiar with the fact that the ABS system on our vehicles (for those who have it) gets confused while on the dyno and often takes a few seconds or minutes to 'reset' once you come off. But I am wondering if when putting the car on the dyno, do they actually disconnect our ABS sensor near the rear end? The reason I ask is because I found that mine was disconnect today (I was wondering why my ABS wasn't resetting like normal after the dyno session) at the rear jumping wire harness.

Seems unlikely that it came unplugged itself. And, it seems to me I've heard others having their ABS disconnected after a dyno run. So, I assume they must unplug it? Is this where they get the speed reading (coming off the rear wheel speed sensors) for the dyno? Sounds logical, but do any of you know for sure?

TIA for the lesson.

 

Most dyno shops will disconnect it from my experience. They also left it disconnected for me once.
Later
Mike

 

Chriss

the dyno gets the speed reading right from ur tires !! hence the use of the rollers

im pretty sure harvey does NOT disconnect the sensor .. as he never did it to my car (been on twice) and have never seen him do it to any other car

there is no reason for the dyno to need a speed sensor from the diff or tranny to do its job !! what about the 80% of the other cars that done have ABS !? lol

and theres really no need to disconnect it !! they dont do it when u goto aircare do they !? u just shut off ur car and turn her back on

reason is . the ABS unit is only online when u have the brake pedel pressed .. thats why we can easily use a line lock and go on the dyno and aircare without any problems

 

Lol! Some of my initial post sounds a little stupid when you put it into perspective like that! Haha!

But this is more along the lines of what I was getting at (and perhaps Mike answered it by stating that he thinks they do disconnect it):

My ABS harness was disconnected underneath my car, and I know I'm not the first to have this happen while on the dyno (do a search the topic and you'll find a fair number of cars that 'mysteriously' have their ABS sensors harnesses unplugged while doing a dyno run). I can't say I've ever seen an ABS wire harness come lose on its own under normal driving conditions. And it shouldn't, the way it clips in. And it shouldn't for safety reasons.

If the shop doesn't disconnect it, is it that driving the car hard (for myself and others) on a dyno causes the harness to pop off? If so, you would think it would come off under any form of 'stress' conditions that the car is subject to, such as racing or hard driving. And that would seem to be quite a safety concern - when you are driving hard is JUST the time when you likely need ABS, and it would be ironic if those were also the type of conditions that caused your ABS to become disconnected. Just when you need it, it isn't there.

So, either they do disconnect it or it is a serious flaw in the wire harness. My bet is on the former.

That goes back to what my initial post was about. Why do they disconnect it? (I think) ABS is still online even if you don't have your foot on the brake because it is used by the TCS/ASR (traction control) - at least on LS1 cars, ABS is applied to the brakes when wheel spin is detected. But if TCS is turned off, then the ABS is fully offline (I think). Nevertheless, even with TCS off, the ABS light will come on during a dyno run since the pcm senses a loss of traction with the front wheels standing still and the rear wheels doing 140 mph (the ABS traction light comes on,. but with TCS off, it can't do anything about it).

Likely then, I can see why they might disconnect the rear wire harness to the back wheels to not confuse the PCM. Why not on all cars then?

Too long of a post....

 

sorry .. didnt read ur whole post !! (too long)

but theres an easier way to find out

call harvery

 

ABS is fully offline until needed ONLY on non-ASR equipped cars. When your ASR switch is turned on, your ABS system is online but dormant until required to either 1. regain traction or 2. safely stop/slow down the car.

 

Lucifer: sounds right to me.

Sideways: now that would be the EASY and LOGICAL way to get the correct answer.