Car stuck in park with engine light on.?

[arbjune]

98 automatic grand am stuck in park. The only way to get it out of park is to pump on the brakes hard. The check engine light is coming on after the breaks are pumped. The brake switch was checked and that is all right. A new throttle position sensor was put in a few days ago because the car was slipping gears and the check engine light came on( error code indicated the tps was bad. The shifter was checked by mechanic and he claims it is bad and they cant find a replacement. When the car was hooked up to the diagnostic sensor the second time, they ran the car but it was saying there was zero voltage from all systems. When the tps was replaced the car registered voltage in all systems. The mechanic is not sure the problem was the tps. The shifter was unlocked and also later the shifter was taken out and readjusted and put back in. The code was cleared after the new tps was put in. Why should the check engine light be coming back on now that the car is having a problem going out of park? Why should the brakes make the check engine light come on? There is enough brake fluid and the transmission fluid is fine.