There is an oxygen sensor right on the exhaust manifold, directly behind the radiator and fan. Follow the spark plug wires down from the top of the motor. From where those wires plug into the coils, go left (assuming you're standing in front of the car ;P). The sensor is the cigar chaped white thing that screws into the exhaust manifold with one wire coming out of it. There may be a second sensor (somewhere "under" the car), some cars have them, not sure about the SL series. Yes, the 99 Saturn SL2 DOHC does have a 2nd O2 sensor, I believe it is located under the car, mounted to the exhaust, after the caddy.
under the air box
The average cost of repairing a clutch on a 1999 Saturn SL is anywhere between $400 to $3000. The Saturn SL was produced from 1990 to 2002.
The knock sensor is located on the backside of the engine to the left of the oil filter, it is round with a 1 wire plug on it and a round base. I do not know the torque spec, but when I replaced mine I made it tight enough not to back out on its own.
were is crankshaft sensor located in 2001 Saturn l300
There is one right in front usually in the exhaust manifold. You may have a secondary one behind the catalytic converter. There is only one sensor until 1996. This is according to the Haynes 1991-1999 Auto Repair Manual.
Check
Engine coolant temperature switch/sensor
The 2002 Saturn IAT sensor can be found on the top of the engine. The IAT sensor will be near the injector fuel pump.
14mm
I do believe you have to get this from the dealership.
in the gas tank
The fuel filter in a 1999 Saturn SL is located inside the frame rail on the driver's side on the left. It is found near the fuel tank, under the master cylinder.