If you ask me, $20 should be the price to pull the pan and check the wiring and solenoids if you bought the gasket, filter, and fluid. I haven't personally done an auto fluid and filter change but its what, like 10 bolts to remove the pan, then you change the filter? and idk if your car is obd1 or ob2 but I believe either way a bad sensor will show up on either of them diagnostics test, either way you should be able to run the ecu signals, if you have the right FSM for your vehicle and test it yourself.