Swamp sensor

Heh there! Apparently I’ve got a built-in swamp detector on my sweet baby Lexus! (Her name is Katie, for future reference.) The “check engine” light came on a couple of years ago, and a local repair shop thinks it is a problem w/ the catalytic converter. However, for well over year now, that light only comes on as we drive into the swampy areas of coastal North Carolina… but when we return to the Piedmont region of rolling hills, that pesky light goes out! The dudes at the repair shop quoted an estimate of $600 or so to replace the catalytic converter – but it seems to me that if it is only “on” when we are in swampy areas, then it must need a new sensor instead. Whadda ya say? Ever heard of a Lexus w/ a swamp sensor? Is this something I can ignore, or should it be changed? So far we’ve been able to schedule inspections in between swamp visits when the light is out. Katie is an awfully sweet car; I don’t want to have this cause her any irreparable problems. Thanks!

Can you post the exact code in the “P0123” format? Most auto parts chains can find them for free (Auto Zone, Advance, etc.)
Probably has something to do with humidity or elevation messing with a sensor.

" Probably has something to do with humidity or elevation messing with a sensor. "

I agree with this and I agree with LexiGirl. I have seen vehicles with a PO420 catalyst code act this way depending on ambient temperature, humidity, elevation, short trip/long trip driving or who knows ?

PO420/PO430 and other catalyst deficient type codes are one of the most common “check engine
light” codes people encounter and a sales generator for new catalytic converters that don’t necessarily resolve the problem.

This whole swamp story comes as no surprise to me. It’s probably a weak sensor(s) problem.

Get the code(s) and if it’s a deficient cat PO420 or PO430 then take a look at this:


Model-Year ?
How Many Miles On It ?
How Much Oil Does It Use ( qt./miles) ?

Did the “dudes at the repair shop” download any fault codes from the ECU? Did they write them on the shop order? Can you copy them here?

If not, if you simply assumed that the light meant you needed a cat converter and asked for a quote, you first need to get the ECU checked. There are literally hindreds of codes, and most are not cat converter related.