That is about what I thought too. After paying the $2300 bill just for the removal and replacement, I now have the engine warning light illuminated constantly. A scan test indicated that it reqired a new oxygen sensor (lambda). Toyota wanted $404 for the front(4 pin pre cat) and $300 for the rear (2 pin post cat). Found one at an auto electrics for $140 (4 pin pre cat). Fitted it, cleared faults by disconnecting battery for a few minutes.....and still the light was illuminated. A mechanic suggested looking at the other logged fault, namely a left knock sensor signal abnormal fault reading....with a string of 7 other faults following. Code 001 1) left knock sensor signal abnormal 2) knock sensor circuit fault 3) sensor be tighten too close or too loose to the cylinder body 4) ignition timing error 5) securing seat of generator or compressor loose 6) too large clearance noise of valve 7) too large bearing wear and tear 8) module fault Code 002 Left O2 sensor output voltage lower than 0.035V or higher than 0.7V, no change for 60 seconds.