Toronto

The engine-problem idiot light went on during a spin in the country - ES300, 1995. Turns out the OBD code is P0420 "Catalyst System Efficiency Below Threshold."

I replaced the cat converter recently after a mandated emissions test showed it to be faulty - and my gas consumption went smartly better. In light of various rusty parts in the exhaust system, to save money I just had the new generic converter welded in at the local muffler shop.

So does that mean it is an O2 sensor? Is there more than one sensor and/or any suggestions about what to replace first? Any need to hurry with the repair, other than pollution considerations?

Many thanks.
Ben

rembo

i dont know about the 95 one but on my 97, the 420 code for me was restriction of the catalyst systeme, i just ovezied it and it work very well!!

ivory98es3

iTrader: (1)

The problem stems from you replacing the OEM cat w/ a generic. The Toyota ECU is very sensitive and will detect even the smallest of changes in readings from the O2 sensor. It doesn't necessarily mean your O2 sensor is bad. I had the same issue with my '98 ES. Replaced the cat, after so many engine cycles, damn CEL came on. I tried everything you could think of to get it to go out. The solution for me was wiring an O2 sensor bypass inline so as to fake out the ECU. I now get no more check engine light.

Toronto

Thanks for insights about after-market cat converter, I gather you are both saying the same thing. Yuck.

For now, the service signal has been canceled. If it is the cat converter and not an O2 sensor, I guess I can live with the light re-appearing although that could possibly mask some other, more serious, issue.

I don't see why, but my average-route mileage went smartly down after the new cat converter was installed, like from under 20 mpg (12.3 L/100km)) to just under 24 mpg (10.9) (and in the summer when riding my bike lots, substantial loss to evaporation). Just a hint in the last tankfull that consumption is getting worse. Not certain of that fact or the diagnostic implications.

In 20 months I need an emissions re-test... car then 15 yrs old! In Ontario, there's a charitable exemption from meeting the standards: no work needs to be done if a careful diagnostic certifies that the owner would have to ante up more than $400 (which includes the cost of the diagnostic, I think) to fix it.

Again, thanks.