1999 Corolla CEL P0136 now P0141

[Tamiya]

Hello,

I got 1999 Toyota Corolla with 140k miles.

Two months ago the check engine light came on-P0136.

Replaced the 02 sensor (post-catalist). Everything worked fine for 2 months, now the check engine light is on with P0141.

The sensor was Bosh plug-in (around $100) so I'm pretty sure that the sensor itself is fine....

Any ideas?

[fishexpo101]

Personally, I would have gone and used a Denso replacement than a Bosch one - myself and others have had issues when using a non-Denso part, as it seems this engine is pretty picky out the sensors / always a risk of an impedance mismatch (quite common).

The P0141 indicates an issue with the heater circuit in the downstream (post-cat) O2 sensor. One way to double check that is to measure resistance across the two black wires (heater circuit). Should not be shorted (basically zero resistance) and should not be open (basically infinite resistance). If the resistance is too high, it could read as a P0141 as well.

Since you had a P0136 (O2 Sensor Circuit Malfunction (Bank 1 Sensor 2) - prior to this new code - that would lead me to suspect that the downstream sensor itself was probably still working. That the problem was more likely related to the wiring/connector running to the O2 sensor instead. I'd double check the wiring to and from the connector. Check the wiring inside the car - make sure there is no damaged insulation on the wires / wires are not crushed, cut, or otherwise damaged. Visual inspection would catch a majority of the possible issues here.