We have had an engine light that comes on when it is wet out. (Usually from rain) Until recently, the codes were not stored in memory. The last time we tried this, there was a 420 code set. Our mechanic said it was the catalytic converter. This vehicle is a 2006 and only has a 100,000 miles on it. Neither of the oxygen sensors have been replaced. The car doesn’t seem to run any differently when the engine light comes on. I don’t disbelieve our mechanic. I just want a second opinion.
Also, what is your take on aftermarket converters? Chrysler wants a LOT of money for theirs!
Based on this information I have no reason to doubt the mechanic’s diagnosis, especially of he looked at the signals from the oxygen sensors. Cat converters do go bad, and 6 years/100,000 miles is a bit early, but not unrealistic if it sees a lot of short trips. You can try changing the downstream oxygen sensor first (I would) and that might help.
Re: the relationship of the weather to the code: when a cat converter becomes marginally efficient, it can get to where it needs to be hotter to do the job, and yours being under the car it may be too cool and water cooled from splash in wet weather. Platinum-palladium’s performance in seperating the oxygen from the nitrogen is directly related to its temperature, and the latter stage of the converter (the conversion of the now-freed oxygen and carbon monoxide to carbon dioxide) is also directly related to the cat’s temperature. As a matter of fact, in new vehicles the primary cat converters are often directly in the exhaust manifold to heat up faster and stay hotter.
Get a “direct-fit OEM replacement” aftermarket converter and you’ll be fine.
I guess I tend to be much more skeptical than mountainbike about both the power of codes and the efforts put out by many mechanics when presented with a code.
A P0420 code is generated by readings that don’t look like what they’re supposed to from the rear O2 sensor. Unfortunately, the usual “text” associated with that is something about the catalyst being below efficiency. What it should say is that the downstream O2 sensor readings are too active in comparison to the upstream sensor.
Given the rain connection, it wouldn’t surprise me if you just had a cracked, frayed or otherwise damaged wire for the downstream O2 sensor. This is not hard to imagine. The sensor and its wiring tend to ride down close to the road. I once had a piece of road debris or something completely wreck the wires on a downstream sensor.
If this was my van, I would pick a dry day and put it on a scantool. I’d check out the readings from upstream and downstream sensors. I’d then “rain” on the downstream sensor with a spray bottle or something and see what happens.
Yes, I do too. Now I need to find an inexpensive code reader that will do live data. I thought the intermittent engine light due to wet conditions sounded like a connection problem, at least, it would on a Harley!
If you have a laptop you can buy very inexpensive little connector gadgets - OBDII plug on one end and USB on the other - that will act as basic code readers & scan tools. There’s are free softwares floating around out there too, such as OBDWiz. They are very basic, but can get the job done for many things.
Walker Exhaust makes a direct fit catalytic convertor for this vehicle (49 state emission-not California).
Chrysler dealers can order these convertors, they are in the Value line catalog. Mopars Value line products are select aftermarket parts and much less expensive than O.E. (brake pads, exhaust, belts, radiators, ect.)
It pays for itself quickly. The first time you don’t pay some about 1.5hr fees for “diagnostics” - well, once you add some working knowledge of what all that info tells you.
swap up and downstream O2 sensors and see if the problem gets bettwr or worse. On live data scanner (cheap $3 ELM327 BT plugin and carscanner app works great) the upstream trace should look like a regular 2-3 per second .2 to .9 spike at warm idle, the downstream should look like a flatline trace with very few blips and only .1v variance. The downstream seeing the same magnitude spikes that the upstream is seeing means the cat is not doing one of its jobs of storing O2 and releasing it to mellow the rich and lean condition the upstream is seeing (and telling the ECU to generate). An exhaust leak very close or past the upstream sensor can fool the downstream into thinking the convertor is bad, Always check for exhaust leaks before replacing anything cat related. I had a 2014 pentastar that had a loose bolt on the cat at the manifold ■■■■■■ that didnt affect the upstream at all as both traces were lock step when comparing banks, but the downstream on bank 2 (front) was way off. swapping sensors didnt change anything. Finding the loose bole and changing the gasket would have made the decision to swap the convertor out much easier to justify.
Since the original thread is 14 years old I doubt anyone is listening to your suggestions. You can check the date of threads by checking in the upper right corner of the post.