After an engine swap and 14 codes, p0420 remains....

[paranoidjack]

In resolving a plethora of codes that came up since I installed my replacement engine, I've replaced fuses, fixed wiring, and replaced both front o2 sensors the other day. I have two new catalytic converters and rear exhaust along with the heated o2 sensors. I have no exhaust leaks.

This code came up today....p0420. Looking in the FSM and googling, seems like no fun. It is indicating catalyst failure, but I have a hard time believing this since the cats are new and custom built. Only 5k on them. I'm hoping the 0420 code will go away, and isn't valid, but I just ordered rear o2 sensors as well to make sure that the entire exhaust system is new.

Has anyone ever had to deal with this code on their fgy33?

[Unnatural1]

I haven't had to diagnosis this code on a Y33 but many times on many other vehicles. Obviously, exhaust leaks upstream from the O2 sensor could cause havoc with their readings and the PCM could see it as a P0420. But, you've checked all that. It would have to be something else.

The upstream O2's are new and we will assume they are ok. It's possible a downstream O2 has gone bad but typically the PCM will set a code for this condition. Still if you already have the sensors, it can't hurt to replace them and give it a shot. But, in my experience with this senario, it's very possible that the catalytic converter is the culprit. I realize you've just replaced them but catalytic converters are not created equal. Many of the less expensive aftermarket units simply will not work well enough for the PCM's of many vehicles to be satisfied.

The only way to really know for sure is to scope the upstream and downstream O2 sensor output and compare them. Many scan tools with datastream capabilities can do the job. Also, a 2 channel digital scope will work brilliantly.

Short of this you are stuck swapping parts, clearing the codes, and trying it.

[paranoidjack]

Thanks for the post. I was thinking it, but fearful since I just bought them. Running rich for some time probably fouled it, I'll assume they were OK from the get. I guess I'll be relegated to buying an aftermarket one and welding it in.

I am getting the new o2 sensors this week and installing them (downstream). I'll reset the ECU and check what happens. I have noticed that for the first time, now that she is "all set," sometimes the car starts and idles very roughly, like it is on 7 cylinders. Good old coilpack issues on the new engine - I'm wondering if it's possible that this could have caused the code (it runs like this briefly once every two days or so). The FSM dictates in a p0420 it could be injectors, so I'm thinking it could be a coilpack since there is no code for that.

Thanks again, I am going to pull coils and test them.

[Unnatural1]

That misfire, if driven too far, could very well damage an otherwise good cat. Misfires allow large amounts of raw fuel downstream to reach the cat. The temperature in the catalytic converter, as a result, will rise to the point that the substrate inside it actually melts down. If the Check Engine (MIL) light comes on and begins flashing, the PCM is detecting a misfire that can damage the cat in this way.

You may try fixing the misfire and clearing the code. After 10-20 miles of driving, rescan the PCM for codes and see if the PCM has run it's monitor tests. If the cat monitor is set you might be ok. Once the engine is sound and running smooth, readdress the P0420 code if it reoccurs.

Also, a bad coil pack can set various codes, depending on the car. The most common codes across the board are P0300-P0308. All of which indicate misfires on a particular cylinder, or random cylinders in the case of P0300.

~Brendan

[paranoidjack]

Will do, thanks for your detailed input. I'll post my results.

[Unnatural1]

No problem...hope some of that helps you.

~Brendan