Low oil pressure. Can be caused by a weak oil pump, or a defective oil pressure sending unit. Can also be that the crankcase is low of oil. Change your oil, use the correct weight and amount, install an AC/Delco, Purolator, Wix, or Bosch oil filter and see if that helps.
http://www.topix.com/forum/autos/chevrolet-impala/T4P2NGT979PJ7QT2P
Evidently the oil level was low before you changed oil and was full thereafter.
Time to change your oil in your engine!
Add brake fluid
It requires a scanner to properly diagnosis a check engine light.
Turn off the radio so that you can hear the chime/beap that the system makes when the tire pressure light is reset. In order to turn off the low tire pressure light on a 2001 Chevy Impala, you pull back on the headlight knob three times - out and in, out and in, out and in. At that time, you will hear a chime or beap. On mine, for whatever reason, sometimes it does not work the first time, and I have to do it again, but by the second time, it always works.
There is one screw that holds the fog light it into place.Unscrew that screw and the fog light will pull out of the bumper.
It can be numerous things. If the check engine light is on then you need to take it to a repair shop and have them diagnosis it for you. You may have to have the cooling system pressure tested for leaks.
The most likely cause is the turn signal flasher.
As per the instructions on page 5-55 of your "Owner's Manual"...
have 1994 Chevrolet G20 van that the anti lock light comes on
It means your alternator (generator) is not charging the battery while the engine is running.