I went to scan a buddies car the other day because it randomly dies on him and won't start. It threw a code, but the battery was dead, so it was erased. The car started and ran fine and the only thing I noticed was that the O2 sensor voltage was different by .5 from the left to the right (ie O2left = .3 and O2right = .8). This is a 94 LT1 car. What does this mean? I wasn't sure if the voltage readings gave indications on rich or lean conditions or not. Thanks for the help guys.

 

Under what conditions did you see those voltage readings?

When the engine starts in open loop/cold, the O2 sensor voltages should both be 450 mV (0.450 V). As the sensors warm up, and with the AIR pump working, the voltages will drop to 00x mV's. Then it goes into closed loop and the O2 sensors should be switching back and forth, from 0xx - 9xx mV's. Since the left and right banks of the engine are independantly controlled there is no reason for both sides to have the same O2 readings at any point in time. The readings are changing approx 9 times per second, so even a scanner may not capture all the readings at the same time.

 

This was at idle and with the engine cold (open loop). The engine started warming up but the sensors kept reading pretty far from eachother (500 mV apart). I know that they are independent, but shouldn't they have "similar" readings? I don't think he has an AIR pump on his car, or atleast it isn't hooked up. He has LT's with no emission hook-ups. What does this voltage mean? Why would they be so different? Thanks for the help.