I have an 03 F150 supercrew 4x4 4.6.
When I start the truck the abs light comes on right away.

The other day I skid on snow to see if the abs would work but they did not.
A minute after that the light went out and the abs worked.

The light stayed off all day until I parked the truck and the abs light came back on.
Any ideas what the problem might be?

 

your best bet would be to get the code, we can play the guess what part needs to be replaced all day long, however if you want to guess at parts replace the wheel speed sensor first, it's in the top center of the rear drive shaft, one bolt holds it in

 

If you start the truck, the computer does a continuity check to see that everything is connected. If the light comes on then, you have a loose connection (most of the time) or broken sensor... after you start moving, (5 MPH) the computer does another check to see that the sensors can measure speed. If you get the light after your rolling, then the sensor can read speed. If you did a front brake job or replaced the hubs, it is common to bend one of the pins in the two prong plug to the ABS. I would clean the two connectors, inspect and reconnect. That being said, if the light comes on after moving or every now and then... the rear sensor sometimes gets weak and dont count the speed right.

 

Well,
I went under the truck yesterday and started checking each sensor and noticed the front left wires going to the sensor were cut.
I reattached everything and now all is good.

 

Does anyone know how the ABS sensors look? or the locations?

I have the same issue here, but no clue.

Thank you.

 

one is in the center of the rear axle, the other 2 are in the front hubs follow the wire going to your wheel

 

Thank you sir, I appreciate the expeditious response.