I have been chasing a fault on my 2000 Avalon for 18 months (after sending it repeatedly to a mechanic for repair. The fault was intermittent engine light (MIL), which eventually came on constantly (after closed-loop warm-up). The fault was diagnosed as knock sensors (OBDII Code PO325/330). The knock sensors were replaced twice and the harness also replaced and the PCM (Powertrain Control Module - computer) was sent away for checking by a specialist. When they still couldn't fix the problem, I had a look at the knock sensor outputs on an oscilloscope. I should mention that if driving the engine hard, the MIL would not illuminate as the computer then only looks at the TPS (throttle position sensor) for ignition timing. I noticed that the knock sensors had different level outputs, so I fitted an amplifier (disused computer sound card amp) with a gain of x2 between the knock sensor leads and the PCM inputs. I have just completed a 4,500Km interstate trip with no further problems with the MIL! So the answer was easy - only fit genuine Toyota Knock Sensors to this engine (which I priced at $263 against after market ones of around $70).
