Finally got to the bottom of my periodical engine check light.

P0420. Catalyst system efficiency below threshold.

So what does it mean?

 

This is what I got out of the OBDII manual. May be a bad O2 sensor after the cat….

 

catalytic converter is not working properly, Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem.

 

+1 to what's said above.
Typically it is the catalyst is 'burnt-out' and no longer functioning as per spec.
High-flow cats sometimes can reveal the same issue/code. Secondary O2 sensor replacement may help, or placing O2 extenders on the secondary 02's

 

Agree with them bad O2 if not probably cat.

 

maybe move the bad o2 sensor from before to after cat or vice versa see if it changes the code, if the code changes then its very likely the sensor

 

^can't swap primary's and secondary's...you can swap secondary's side to side though...

 

Thanks chaps. Apart from hurting the environment is this a problem? Also do tune cars exhibit this fault? Especially change of exhaust?

 

tuned cars can have the secondary O2's 'shut-off' so no CEL comes on.
Root cause is the catalyst is not functioning up to spec(or the O2's aren't within spec any longer) or is a high-flow cat that doesn't meet the emission-scrubbing requirements set by ECU

 

But apart from catalyst efficiency I presume this means exhaust fumes are dirtier but there is no other ill effects?

 

no effect on anything but what you see/smell out the pipe

 

The converter is not able to store oxygen.

This is usually a sign the converter is bad.

The general rule -- from the factory manual at any rate -- is if there are any aging O2 sensor codes to replace the indicated sensors and clear the codes and road test the car.

If the converter code comes back to replace the indicated converter.

I had a Boxster generate a P0430 off and on for several years.

Recently I finally decided to do something about it when I had the car in and the tech confirmed the severe rattle/buzzing was not loose heat shields but a loose brick in the converter.

I bought two used converters and had the tech install them and the noise went away. After several thousand miles the P0430 or any other codes have not shown up and the engine is running better than ever with over 281K miles on it I might add.

As an aside, I did find switching from running discount gasoline to running (mainly) Shell V-power reduced the frequency of the P0430 error code but it still came back when driving in cooler weather.

With the old converter not storing oxygen properly the DME was probably adjusting the mixture to help the converter and as a result fueling was not optimum.

If your car is stock you are probably looking at converter replacement to eliminate the error code, though of course, mind the sensors if there are any sensor errors.

If you have a modified car with possibly a different from stock "tune" then this opens up a whole can of worms.

 

Different can of worms then as my car is tuned. :-(.

 

Still the question remains; apart from bad converter causing more pollution any hazard to the car?

 

Chances of hurting motor are slim, may hurt cats if running rich with bad o2. The car would run optimum with new o2 if that is the problem. If the cats bad your exhaust would be dirtier but shouldn't hurt the engine performance unless plugged.