Hello,

I have a stock 94 firebird lt1 with an o2 sensor problem. The o2 sensor voltage never changes on both sides its always 450mv. I replaced both sensors and the problem is still there. I checked all the wiring and conectors. Heater circut works fine as well. I jumpered the signal wires to ground and the voltage drops like it should. I followed the troubleshooting chart and it points to bad O2 sensors again. Could I have gotten two bad new sensors, or could somthing be killing them right away. Any good ways to test the sensor itself?

Thanks

 

450mV means the sensors are cold, or there is an open circuit. 450mV is what the PCM applies to the sensing thimble, so the thimble can generate +/- millivolts, based on the difference in oxygen partial pressure between the exhaust gas on the inside of the thimble, and ambient air on the outside of the thimble. In essence, the PCM is reporting its own internal voltage on those circuits.

You say you "jumpered the signal wires to ground".... there is a signal wire and a ground wire for each sensor, routed back to the pins on the PCM.

I've tested the sensors by unplugging the sensor, and hooking the sensor's signal wire and ground wire up to a volt meter (use only a high impedance digital volt meter), and heating the sensor shield with a propane torch. Should produce a reading, and it should vary with how directly you apply the tip of the flame to the metal shield on the sensor.

 

Or hook up the internal heater and wait for it to heat up, then using a cig lighter, inject butane into the thimble (to displace the o2) and the milivolts will immediately rise.

 

I've had this happen to me when I installed 2 sensors that were suppose to be Delco units but were not. After I installed 2 older sensors they started reading again. What brand sensors did you get?