Scan Tools And Turning Off ABS Dump Valve While Vehicle Is Moving

[George7941]

I have a very slight pulsing on the brake pedal while braking. Want to see if it is the left front or right front or both, so I hooked up my Tech 2, drove the truck and hit the LF Dump Valve On, and got a message saying it cannot be done while the vehicle is moving.

Is there a scan tool that can do what I want? Is the ABS module programmed such that this request will always be ignored?

 

[Jetronic]

You'd best look at wheel speeds. I don't know of any abs systems that allow what you want

 

[George7941]

Slight brake pedal pulsing won't generate wheel slip and, hence, variation in wheel speed. Thanks anyway.

 

[Timmastertech]

Most manufacturers will not allow you to activate ABS valves while moving, some even turn off scan tool communication with the ABS over certain speeds like Honda.

 

[Jetronic]

Slight brake pedal pulsing won't generate wheel slip and, hence, variation in wheel speed. Thanks anyway.

I see you have zero experience with ABS systems. The wheel speed variation might be there already, and causing the pulsing. Well, the variation isn't there, but the wheel speed sensor could be fooled by a bad tone ring. 1 mph can be enough for some systems to cause abs activation under any braking.

 

[George7941]

I see you have zero experience with ABS systems. The wheel speed variation might be there already, and causing the pulsing. Well, the variation isn't there, but the wheel speed sensor could be fooled by a bad tone ring. 1 mph can be enough for some systems to cause abs activation under any braking.

That is easy enough to check. I will pull the ABS fuse and see if the pulsing is still there.

 

[Jetronic]

There's more than 1 abs fuse, but the diagnostics equipment can tell you wheel speeds aswell sao you know which wheel it is.

 

[clinebarger]

You should be able to tell/feel if the ABS is activating under false wheel speed sensor input. Don't just assume that pedal pulsation is from the front brakes....Especially on rear Drum brake equipped GMT800's.