Catalytic Converters

[nobody >]

The sensor being bad isn't the only thing that will make it not
"switch". If the engine is too rich, or too lean, or has an exhaust
leak ahead of the sensor, it will read as bad. Other possible causes
as well.

Also, the converter does not need to be BAD to not work. If it never
gets lean enough or rich enough to function properly it will fail it's
efficiency test.The nasty exhaust leak before the converter can and
will do this.

I don't know if it would throw a code (it usually doesn't), but possibly
the engine temp sensor (not the gage/light sender) could be defective.
If the sensor reads as "always cold", the mixture would be rich, hot >>
lean.

Scientific Wild-Assed Guess...

 

[Remco]

I don't know if it would throw a code (it usually doesn't), but possibly
the engine temp sensor (not the gage/light sender) could be defective.
If the sensor reads as "always cold", the mixture would be rich, hot >>
lean.

Scientific Wild-Assed Guess...

I've had that happen to another subie years ago:
Not sure if that still holds true with the newer models but certainly
the 93 Impreza became very hard to start, when that sensor went bad.

 

[Carl 1 Lucky Texan]

I've had that happen to another subie years ago:
Not sure if that still holds true with the newer models but certainly
the 93 Impreza became very hard to start, when that sensor went bad.

Another WAG, are you losing coolant? I think it can quickly destroy the
front O2 sensor.


Carl

 

[Remco]

Another WAG, are you losing coolant? I think it can quickly destroy the
front O2 sensor.

Carl

Good thought, Carl, but nope, no problems other than the p0420 code.

 

[clare]

Good thought, Carl, but nope, no problems other than the p0420 code.

Load up the tank with known 0% etanol fuel, and 99.9% sure the p0420
will go away. It is a calibration issue.
On Hondas it is a problem and there is a TSB that addresses it - a
reflash of the PCM to accept E10 without triggering the CEL.