codes po141 and po171

[fastmoney]

03 Alero 2.2 with no maf sensor.

I have both codes 141, 171. I am trying to figure out if I should just change rear oxygen sensor or something else.

[Tech II]

These are two separate situations....

P0171 means the pre O2 sensor is reading a lean condition.....low fuel pressure, a vac leak, an exhaust leak, etc.

P0141 means the post O2 sensor is taking too long to respond at startup, because there is a problem with the heater circuit......before you think of replacing that O2 sensor, you should check if the fuse for the heater circuit is blown, or the harness to the circuit is open, only way to check is disconnect harness and check the heater circuit with a test light on start up.....it should light for a certain length of time.....if it does, then the sensor should be replaced.....this is a 4 wire sensor....2 for the O2 data, 2 for the heater circuit...

[fastmoney]

OK I will check the fuse. I checked the circuit with a volt meter and I got a reading of 12.5 or so, not sure if that works the same as a test light.


So if it is a bad o2 sensor and I change it , that will not correct the po171, is what your saying?

[Tech II]

That is correct....

The P0141 is for the O2 sensor heater circuit for the sensor after the cat....this circuit gets the O2 sensor working quicker.....this sensor is only used for catalyst efficiency....

The P0171, is for the O2 sensor in front of the cat.....this controls fuel air ratio....it could be a bad sensor, or it could be what affects the sensor like an Exhaust leak, vacuum leak, etc.

But neither code affects the other...they are separate issues.....the P0171 is the more important of the two....