Emissions Readiness Monitors

[LPSIII]

96 jeep will not pass emissions because OBDII diagnostics montitor say O2 sensors not ready. have no codes. what should I do.

[xj31]

I haven't really heard it stated like that,but what I think it is is the o2 heater monitor hasn't run.Basically what happens is on a cold start,the pcm watches how fast the o2 sensor voltages come down.When they are cold,they dont' work as well.They usually read abot 5 volts until they warm up.They have heaters built in that are controlled by the pcm.As they warm up the voltage comes down and the pcm sees that and if it happens fast enough then it is considered to be working properly.You don't get a check engine light because the sensor is still working.If you have access to a good scanner you can find out exactly what it is,and if it is the o2 heater monitor. you can test it and see which o2 sensor it is.Otherwise if you like to guess you can replace both o2 sensors.

[LPSIII]

Originally Posted by xj31

I haven't really heard it stated like that,but what I think it is is the o2 heater monitor hasn't run.Basically what happens is on a cold start,the pcm watches how fast the o2 sensor voltages come down.When they are cold,they dont' work as well.They usually read abot 5 volts until they warm up.They have heaters built in that are controlled by the pcm.As they warm up the voltage comes down and the pcm sees that and if it happens fast enough then it is considered to be working properly.You don't get a check engine light because the sensor is still working.If you have access to a good scanner you can find out exactly what it is,and if it is the o2 heater monitor. you can test it and see which o2 sensor it is.Otherwise if you like to guess you can replace both o2 sensors.

Thanks
I will have to find a scanner to read it out. O2 heater Not ready was one of the Not ready monitors along with the Catalytic Convertor efficiency and O2 Sensors.

[xj31]

did you just clear the codes or disconnect the battery recently?When you do either of those it resets the monitors.Its to keep people from trying to beat the emmision test by turning the light off to pass the test.