Roomba 4000 runs ok 4 short time then stops upon hitting obstacl

\015 My Roomba Model 4000 will run properly often for several minutes but upon hitting multiple obstacles, will shut down and sound the double beep “oh oh” that Irobot says is associated with a wheel off the floor. On average, it probably requires 10-20 obstacles before the problem occurs. I’ve cleaned around the wheels as best I can. I’m not sure if this is a sensor problem or perhaps a loose connection that breaks temporarily from the force associated with hitting the obstacle. It always restarts when I press the clean button. Are there service manuals available for these?\015 – Roomba Robotic Floor Bagless Vacuum