Clogged catalytic convertors will not cause this code. it is for a circuit fault, and from the sound of it, it is a hard fault. (meaning it is occuring right now.) it is also for the left side downstream sensor. (the front bank of cylinders) check all the connectors between the sensor and the pcm. A good place to start is the three connectors on the passenger side near the rear of the engine compartment attached to the engine. I've seen these come loose more times than I can count. You can also check the reisistance of the wiring between the sensor and pcm. If the wiring checks out ok, and the sensor is capable of generating a voltage of about .9 volts during a rich condition, the pcm is at fault. 99 times out of 100 the problem lies outside the pcm, however. If you can't find the circuit fault, try overlaying the harness. Run two wires from the sensor to the pcm along the factory harness. Use some convolute tubing if you can find some. Do not, however, solder the wires. (use crimp splices and heat shrink tubing) This setup draws air around the small spaces between the stranded wire from the pcm down to the sensor and uses this air to compare against the oxygen content of the exhaust. Good luck.
