will an upstream oxygen sensor work if the flex pipe is loose on a '01 Hyundai??? Thanks!!!?

Question

with a new sensor the check light came on again. THEN with a new one it came on again the next day. WHY?

Answer 1

Fix your flex pipe.....

O2 Sensor? Probably NOT the problem.
People like to blame the O2 sensor for the problem because that's where the computer fault appears.
However, nine times out of ten, it's not faulty. It is simply reading a condition in the engine that is causing it to send a signal to the computer that there is a fault in the exhaust emissions mixture.
A fouled spark plug, loose spark plug wire, a vacuum leak, dirty injectors, EGR valve, weak fuel pump, dirty fuel filter, weak ignition coil, plugged air filter, on and on, can all cause the O2 sensor to register a fault code.
Before you yank the O2 sensor and replace it, check the basics first. Otherwise, you could have wasted time and money on the result, not the cause.