I have a 1998 Dodge mid size pick-um-up, with 96k miles, big V-8, automatic. Drive it one day and park it, week later start it up and the ABS light and brake light is lit, half a pedal on the break. Why question is, how in the heck can a truck have a problem while sitting still? Is it because it is a Dodge? What is the cure? (can't junk it, just in case that is an answer)
I have a 99 with ABS in the rear only, and it did the same thing. Is your speed ometer work OK, if not it may be the sensor on top of the rear end housing.
Might want to try a bleeding the break system, may have some dirt or moisture.
Might have a master cylinder going bad.
Yes, fluid is good, odometer is okay, this happen during the extreme cold we had, even though I did not drive it then. I will have the stuff under the truck checked. I'm a good watch and clockmaker but don't know nuthin' bout this stuff.
Other repair shop put a electronic reader on and it showed no fault found. Still half a pedal and the ABS light and Brake light are still lit. They can be reset and when I start the truck both lights are out. Now the crazy part, if I gently tap the brakes a couple times then come to a stop the darn lights don't come on and the brake pedal is full until the next stop.
I have a 2004 Ram and my rear speeds sensor broke. It happened on the really cold day last week. My ABS light and brake light came on but the speedometer also didn't work. Moister must have gotten in the sensor and the cold weather broke the sensor apart. I had to remove the cover on the rear and clean out the broken parts from the sensor. I doesn't sound like you have the same problem but I figure I pass on what I went through with my truck.
Try driving in a straight line and apply brakes...if they seem okay, then drive a short distance and make a sharp turn in either direction. If after coming out of the turn the pedal seems soft and the abs light comes on then its a good bet you have a bad wheel bearing. The play in the bearing will allow the brake rotor to wobble enough to force the caliper piston back on a turn so then the pedal seems soft until you pump the pedal a few times. Just a thought from old truck mechanic.