Downstream oxygen sensor

[Rally Sport]

What does it mean when my 08 Buick lacrosse cx 3.8 V6 shows code p0142 but on the OBD scanner the oxygen sensor checks out it also said no activity but it is reading normal on the OBD scanner?

 

[RD_Atlanta]

It's likely that while you see activity on the scanner, the PCM is not satisfied in the activity is monitors. These PCM wants to see 'X' number of voltage swings from the O2 cell or it will flag P0142. The most common cause is the heater is not working. The heater brings the O2 cell up to the needed temperature to achieve the 'X' voltage transitions / second. It may be as simple as an open circuit heater which can be checked with an ohm meter. If the heater checks out, then its a matter of verifying if 12v is making it to the heater. If not, work upstream from there. If 12v is reaching the heater, it still could be a faulty O2 sensor. I personally keep a spare of most critical sensors (such as an O2 sensor) in the trunk for those situations, just to rule out a bad O2 sensor.

 

[Rally Sport]

It's likely that while you see activity on the scanner, the PCM is not satisfied in the activity is monitors. These PCM wants to see 'X' number of voltage swings from the O2 cell or it will flag P0142. The most common cause is the heater is not working. The heater brings the O2 cell up to the needed temperature to achieve the 'X' voltage transitions / second. It may be as simple as an open circuit heater which can be checked with an ohm meter. If the heater checks out, then its a matter of verifying if 12v is making it to the heater. If not, work upstream from there. If 12v is reaching the heater, it still could be a faulty O2 sensor. I personally keep a spare of most critical sensors (such as an O2 sensor) in the trunk for those situations, just to rule out a bad O2 sensor.

Everything on the 02 sensor checks out that’s what’s confusing me about it.

 

[Rally Sport]

Everything on the 02 sensor checks out that’s what’s confusing me about it.

The OBD scanner shows it checked off with the rest of the other monitors

 

[RD_Atlanta]

Everything on the 02 sensor checks out that’s what’s confusing me about it.

If 12v is reaching the heater and your sure the heater measures good, then it might be prudent to replace the sensor to see if the PCM then becomes satisfied with the number of transitions/ second.

 

[RD_Atlanta]

If 12v is reaching the heater and your sure the heater measures good, then it might be prudent to replace the sensor to see if the PCM then becomes satisfied with the number of transitions/ second.

I should add, you looking at the activity on a scanner is not near fast enough to see how quick these transitions are, you'd need to monitor the O2 output with an oscilloscope to appreciate how fast these are. I would personally try swapping the O2 sensor if the heater checks out and there is 12v reaching the heater. Perhaps other members can weigh in if they have any other ideas.