Abs operates at low brake pressure.

[01SS]

I have a 2003 vy one tonner and intermittently when under light braking in a straight line or light braking and turning, the abs operates and the pedal vibrates. The car has 350km on it and is well serviced and runs great.
I'm wondering if it would be a sensor problem or a module problem?
Has anyone encountered this before?

 

[mechanic]

check sensors for debris (metal shavings or objects stuck to the magnet)
Check tone wheels for shape/debris

Use scan tool or oscilloscope to graph each sensor. When ABS operates check each signal for a change.

 

[01SS]

Sensors don't look bad, nothing stuck in there. Will the scan tool record things like that? It doesn't happen all the time, it's intermittent, once or twice the abs symbol has come up on the lcd screen for a few minutes, then goes away. But that has only happened once or twice.

 

[_R_J_K_]

Should be able to pull the ABS fuse and do some driving to see if the brakes feel any different from normal. Off the top of my head it could point to an issue with the loom, like there might be a nick in the conduit somewhere down the line or it's getting some interference from somewhere or a sensor could be misaligned or just a sensor is just little bit borked.

Replacement sensors look to be pretty cheap and they're not hard to change, so you could buy some cheapies for testing and then get a genuine one if it turns out to fix it.

 

[mechanic]

Will the scan tool record things like that?

Yes. Live data will show each wheel sensor speed.
Depending on the scan tool you may be able to select and graph each sensor for easy viewing.
Some scan tools have a data record function. You select a bunch of sensors on screen and it records on a constant loop, then when a problem occurs you hit save.

Of course, don't drive and watch your scan tool at the same time.

 

[Trevor loves holden.]

Can you unplug one sensor at a time to see which one is causing the problem, Sounds like one of the relays in the module is staying open.

 

[01SS]

I've taken the rear sensors out and cleaned them, they were covered in a few mm of like metal dust. The front ones are in the hub so I just cleaned the plug and made sure was a good connection, so I will see if the clean fixes it, so far it has been good, but need more time to tell. Will see before I need to start replacing things.
I love my old girls, but few little gremlins creeping in.