My 2000 S430 has had a slew of secondary air pump failures. I attributed to used units... so finally popped for a new one with new relay. It failed after a couple days in the car. I have since installed a test lamp in front of the windshield so I can see when the relay activates. The light comes on when the car is first started ( when cold ) and stays on for about one minute max as expected. The curious thing is that it sometimes comes on when I come to a stop and idle at traffic lights even after the car is at operating temps. When the gas pedal is depressed and I start to move again, it goes off. Can anyone tell me what conditions would trigger the air pump? Wondering if the O2 sensors reading something strange could cause the ECU to do this. Or do I have a short circuit? Hope not!