ABS System Self Test

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My truck ABS does not do it.

The FSM says the system runs the pump briefly and activates the solenoids after the ignition is turned ON. I have never heard the pump on, even briefly, other than during an actual ABS braking event. It is hard to miss the growl of the ABS pump.

I installed a scope at the ABS system fuse to monitor the current draw. With the Tech2 I can activate the pump and the solenoids and see the corresponding current draw on the scope. However, turning the ignition on and even starting the engine, the only current draw is the system relay being turned on. The pump and the solenoids are never activated.

Does anybody actually hear the ABS pump being tested at ignition ON?
 
Forgot to mention, I even drove the truck with the scope on, took the truck to about 20 km/hr and still no test.

This was in the parking lot, maybe I should take it out on the road at higher speeds.
 
Originally Posted By: JTK
Lots of vehicles do it once you reach ~10mph.


My 2002 does it from 10-14 mph. I heard it for years and always assumed it was something to do with the 1-2 transmission shift. I've never heard it on my 1999 but it's supposed to self-test when the key is turned ON. There's a lot of noise at that instant.
 
Originally Posted By: Quattro Pete
Originally Posted By: JTK
Lots of vehicles do it once you reach ~10mph.

Yup. That's when I hear it in my 530i.


Yep, my van and my old Focus do the same thing give or take. I've never heard it in the Fusion though.
 
So far a pattern seems to be emerging - Sierra, Camaro and Escalade cannot be heard or felt testing.

Hope we hear from more GM owners.
 
GM used several different ABS systems as well. A Lumina I did brakes on had a Delco-Moraine system - if you listen closely, you could hear the ABS modulator click after the engine is started.

The Bosch/Denso systems in my family's fleet you can definitely hear a clunk or a buzz when you back out of the garage or pull away but the Prius brake-by-wire doesn't have an self-test that runs when the car is moving off, rather the system activates itself when the driver's door is opened and you can hear the relays actuate.
 
Some vehicles are more noticeable than others. I have been in some rentals/loaners where they are completely unnoticeable. A friend of mien has an accord that makes a groaning noise ... not the ABS noise, but a groaning noise. Really odd. My Focus makes a clunk like I hit a pot hole.

My Jeep makes no ABS self check
shocked.gif
 
Can't hear much in my '11 NNBS engine bay over the cacophony of 5.3 LS mechanical perfection.
smile.gif


The brake pedal does, however, pulse once very gently after the first (~5-mph) drive-away of each journey.
It'll even do it key on engine off.
 
I don't remember hearing it on my previous truck, 2012 Chevy Silverado. I don't think I hear it on my current GMC Sierra.

On the other hand very easy to hear on our Forester.
 
Just checked with the scope again, this time more carefully.

The solenoids are exercised within a couple of seconds of ignition ON. This cannot be heard or felt.

The scope shows that the ABS pump is turned on for 25 ms as soon as the vehicle begins to move. I have not heard it so far but I am going to listen very carefully, I should be able to hear the pump even if it is turned on for only 25 ms.
 
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