One emission code after another

[tsg234]

I have a 1999 Solara with the 3.0 V6, a while ago the check engine light came on with the P0135 (O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) so I put in a bosch O2 sensor with the OE harness. No more than 50 miles later the check engine light is on again, but with a new code P0420 (catalyst system efficiency below threshold bank 1) does anyone have any idea what could be going on here?

[bronzemaxell]

Originally Posted by tsg234

I have a 1999 Solara with the 3.0 V6, a while ago the check engine light came on with the P0135 (O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) so I put in a bosch O2 sensor with the OE harness. No more than 50 miles later the check engine light is on again, but with a new code P0420 (catalyst system efficiency below threshold bank 1) does anyone have any idea what could be going on here?

it is very possible that the p0420 is caused by your new bosch oxygen sensor
toyota is very picky about that sensor, i've seen most use denso only.

or you let the P0135 stay extended long period of time, and caused damage to the cat.

[fenixus]

I would replace the post-cat o2 sensor under car with Denso OE or NGK/NTK OE (better insulation on wires over Denso OE). Denso 234-4137 is the OE replacement, prices from $70 on amazon. NGK might be a little more expensive ($90 or so).

Cat monitoring is basically done by comparing oxygen levels between upstream sensors and the downstream. if they do not differ much then ECU assumes the cat is not working.

Also as above, I would avoid upstream Bosch sensors, especially the Air Fuel Ratio sensors, you want the best fit on this one, not the cheapest price, go with Denso OE AFR (as cheap as $104 on amazon) or NGK OE (expensive AFRs, no good deals anywhere for 1mz-fe).

upstream AFRs are used on Calif emission specs, most Solaras are built to meet them. I honeslty haven't seen a federal emission specs Solara yet.