I installed new front brake pads on my 2001 Grand Am GT and now the pedal feels spongy, With the engine running, I can push it all the way to the floor. Did I mess up by pushing the caliper pistons back into the caliper and if so do I have to reset the ABS unit? I have a scan tool but I am not sure if it has this function..

You'll need to look for fluid leaks. If anything was done incorrectly, the caliper was likely pinched, which typically shows as a leak. Also check brake lines in the area in the event moving stuff around upset something also.

Did you pump it to the floor a bunch of times?

Depending on how much clearance is left when you put it back together, it might take a few pumps to get the pads back to the rotors.

Exactly what did you do?

Just replace the front pads? Did you turn/replace front rotors? Clean the interference points? Lube the sliding pins?
Was fluid low in the reservoir before the job was done?
Was the system ever opened up, i.e., a brake line?
With the engine not running, did you slowly pump the brakes and get a pedal? Keeping your foot on the pedal, start car....does the pedal drop? If yes, Shut the car off and pump the brakes again until a hard pedal....take foot off the break pedal.....start car...now apply brakes...does it drop to the floor?
Before you did brakes, was the pedal ok? Are the rears, drums or disc? If drums, try adjusting them....

Update - when I bought this 2001 Grand Am GT, the ABS, Trac Off, and Service Vehicle soon lights were on. Depressing the ETS switch made no difference in the Trac Off light. The DTC showed PO135, open or short circuit at RF wheel sensor. Earlier, I had tested the sensor by putting an ohm meter across the terminals and spinning the wheel. The meter fluctuated as it should. I also had a wheel bearing that was making noise and I found a good deal on a set of four new hubs so replaced them all. After that, I had the front rotors turned and installed new pads. After it was all done, the aformentioned lights remained lit. I had a good firm pedal with the engine off but with the engine running I could force the pedal almost to the floor. When I test drove the car and did a hard braking stop, the left front and right rear wheels locked up and the car began to skid sideways.

Next I tried bleeding all four wheels. I found no air in them and no leaks anywhere. I also tested the vacuum booster per the Haynes manual - run engine for a minute or two, then apply brake with engine off; pedal should become firmer after one or two pumps - it did. Then apply brake pedal with engine running then turn engine off and pedal should not go down any further - it didn't. So it appears the vacuum and hydraulic systems are okay. The Haynes manual also says to open the bleeder screws on the controller and bleed it also but there are no bleeders on the control unit.

Today I did some diagnostics and found that one of the terminals on the harness side of the RF wheel sensor was open. I checked continuity in the the green wire and brown wire at the controller located underneath the battery on the frame rail. I peeled back the plastic shroud and found the hard plastic sheath broken in several places. At one of these breaks, about an inch and a half from the sensor, the brown wire was broken. I soldered the wire back together, and covered it with shrink tubing.

All three lights on the dash went out, and the pedal feels firm, going down only slightly when the engine is started. The ETS light now works and the Trac Off light only comes on when the ETS is disengaged. My theory is that with no signal coming from the RF wheel sensor, the control unit had no way of knowing how much pressure to apply, and since the master cylinder works diagonally, this would mean lack of pressure to the left rear also. Only the LF and RR wheels were getting the proper feed, and too much at that, because they would lock up. I could be way off on this, and I haven't test drove the vehicle yet, but repairing the RF sensor circuit seems to have solved the problem.

Correction - the DTC for the RF wheel sensor open or shorted was C1233.

I was really confused by Post #5, because that code was for the rear....and then your test with an ohm meter?

You use the ohm meter just to read resistance.......you use the A/C scale to check output when you rotate the bearing.....

Having an ABS harness failure problem is quite common........

You kind of complicated your post by making it sound like it was a bleeding problem, when it actually was an ABS problem....

But you figured it out yourself, so kudo'* to you....

You are correct, thanks for making the correction. I was unable to find any wiring schematics for the ABS system or a diagnosis description. I bought a Haynes manual, but they are sadly lacking in diagnostics. Perhaps you can answer a question. I was attempting to find a break in the harness by probing the green and brown wires, checking continuity from where it comes out (or goes into) the electronic controller, then probing the other end where it plugs in to the wheel sensor connector. For test purposes, I also probed the yellow wire that goes to the left front sensor. Both sensor harnesses also have a green wire. On the left front side, it didn't seem to matter whether I probed the yellow or green wire, either way I got a 40 - 41k ohm reading on both terminals at the sensor end of the harness. Note, the harness was still plugged in to the control unit and unplugged from the wheel sensor. On the right front side, I got 40 - 41k ohm on both terminals when I probed the green wire. It was only because I got an infinite reading on the brown wire on the right front side, that I discovered the broken wire. I am not sure why I got readings of 40-41k ohm on the other circuits. It should have been close to zero, unless these are resistance wires? And why did I get a reading at both terminals while probing just one wire?

Thanks again for your input, I will update on the car later, I have a few more minor repairs to perform before the next test drive.

Resistance tests are far from being the best. A load test is the best way but when you have an open circuit it'* probably going to be found using the ohms settings.

When you are testing the harness for a circuit, you check for continuity.....you do this by disconnecting both ends, and checking one wire at a time......a good circuit is zero ohms, bad is infinite/open circuit.....anything in between is not good....

You would need a schematic of the harness at the abs controller to know which circuit to attach to....

Those harness circuits are made up of multiple fine wires, to allow for flexing and movement, and yet they still break.....