Hello All

My 2005 RX330 popped codes P0420 and C1201. The ODB Reader says Catalyst System Efficiency Below Threshold Bank 1.

I'd like to try replacing the O2 sensors in Bank 1 before fooling with the Catalytic Converter. For that matter, I'll also give the MAF sensor a cleaning.

How do I know which sensor I should try to replace first?

 

Well, P0420 is bank one so those would be o2 sensors on the firewall side exhaust. Search the forms for p0420, others have had it. Some used cata-clean and other cleaners, higher octane fuel, etc and have gotten rid of that code. A friends Subaru had that code and I reset it for him with a scan tool from the motor pool and it stayed gone, so I'd start there. C1201 is VSC off or something like that (this happens automatically when another code is stored), fix p0420 and it will go away.

 

In my case, when I first purchased the vehicle the Code P0420 & P0430 kept coming back once erased, the issue was the previous owner most likely pumped in the cheapest fuel possible for years....
leading to a buildup of carbon & deposits.
I did clean the MAF Sensor it was a deep dark blackish red then kept refueling with premium, eventually the code never came back, now I am refiling with 89 mid-grade, no codes.

 

See attached photo. Is my MAF dirty?

 

Normally a clean MAF Sensor is more clear with a red color.....
that MAF sensor shows carbon deposits.

 

Try using this...

 

So if this o2 sensor is "on the firewall side exhaust", than this would be the downstream sensor?

 

no. Both banks have upstream and downstream. Bank 1 is against firewall, bank 2 at front of engine. Upstream is at or near manifold where exhaust first leaves engine through valvetrain. Downstream will be the second in that system down the exhaust further on a catalytic converter. The code will say which bank and upstream or downstream

 

So I bought one of those wifi OBD scanners and it seems to be telling me that I'm not getting any voltage on O2 Sensor 1.

Am I doing something wrong?

Is the sensor bad? If so, what bank and what sensor?

What other features in this app would help me diagnose my problem?

 

Thanks. I used this but no dice. The CEL popped again.

 

I can't wrap my head around this. Shameless bumpage.

 

If you still have p0420 present and no voltage on sensor 1 as indicated, then you should start with testing the Bank 1 upstream o2 sensor. Firewall side of car and probably hard to access.

 

How do I access this?

 

That's a good question and I've never attempted to. Perhaps someone on here who has will chime in. I just understand the engine layout, etc. Here's what I would try:
Remove all the belly pans under your engine and look up at it. It will be bolted into the bank 1 exhaust manifold on the backside of the engine. I've been under my car before and seen the Bank1 sensor 2 near the rack. Find it and follow that portion of the exhaust up. The next sensor up will be the upstream Bank 1 sensor. Hope that helps.

 

So my RX330 2005 now showed up with P0430 code. I use Eric way of debugging the problem by checking temp before and after the CAT for both CATs. The temp in the after the CAT is roughly 20-30 degree higher than before CAT. Is this normal or too low of a difference (some said between 100-150 is expected)? I checked the O2 voltage for both banks using my scanner tool and got both Bank 1 and 2 O2 Sensor 2 is roughly 0.4 to 0.7 volt. However, for Bank1 and 2 O2 sensor 1, I got 3 volts or so. Is this expected or both Sensors need to be < 1 volt?

I plan to use seafoam to clean by going through the throttle port since some people who has done so have fixed the code.

Any help would be greatly appreciated.