Hi All,
My car is a 2013 Lexus GS350 that has over 120k miles, and lived all of its life in the rust belt.
About a week ago my car threw a P0430 code, Catalyst System Efficiency Below Threshold (Bank 2). After a couple days of driving, the code went away by itself. I hadn't noticed any changes to the way the car drove so I was not too concerned.
Yesterday the code came back, again it was P0430. This time, I cleared the code before my morning commute ~20 miles. When I parked I had no codes. I decided to let the car idle for a bit and check for codes even though the CEL was not turned on. The code that popped up was P0420, Catalyst System Efficiency Below Threshold (Bank 1).

I figured that the P0430 DTC would mean that I need a new catalytic converter. But also getting the P0420 could indicate an exhaust leak that I am not hearing.

Has anyone else had these issues, and could you help me figure out a way to diagnose it? Would plugging up the exhaust help locate possible leaks?

 

Your main culprits are:

1. Gas leakage from exhaust system
2. A/F sensor (up stream)
3. HO2 sensor (downstream)
4. Three-Way Catalytic Converter (TWC)

Many people go right to the TWC since that what the code says. You will find, Lexus cats are not cheap. Aftermarket cats are hit and miss.

Since you are throwing both P0420 and P0430 (both exhaust sides) I'd eliminate exhaust leaks 1st then move on to HO2 sensors. Also double check electrical connections to the sensors. Clean and re-snap if possible. Plugging the exhaust could help find a severe leak, but it may be best to take it to an exhaust specialist to check the gaskets or check for a rusted out exhaust system.

Good luck.

 

@revesalex I'm sure the signs/symptoms are there but you didn't mention any: does the car seem to be using more fuel than usual? Does it feel sluggish even if you're in sport mode and mash the accelerator?

Those codes are usually spot on in terms of needing to check your exhaust system components. However, as fellow member @93SCMax articulated already, i'd also have your mechanic look into your oxygen sensors to see if there is a problem. Check the MAF sensor as well.

The codes will keep coming back even if you clear them because something is amiss. I know from my experience at 90k miles with my previous 2GS. I will say my older car ended up needing a new catalytic convertor...and once it was in, the car felt like brand new. A pricey fix at any mileage, but hopefully its not your cats but something simpler.

 

I'd agree with @93SCMax and add a possible faulty EGR valve and/or rotted tube. Had these same codes with my 300k/mi. 2002 Camry XLE v6. I replaced all of the above and the p0430 kept coming back. I replaced an O2 sensor for a 2nd time and the code went away for a few weeks, only to come back. In the end, I think I had an internal oil leak that was fouling the O2 sensor and after all the fixes traded it in for my GS350. I wasn't going to put any more money into it and I probably should have quit long before that point.

 

Normally if it's going off and back on again is Not the Sensor itself. It reading exhaust outside of the values Lexus wants. Soon it will likely code and stay on from experience.

If was my car I would do a upper engine intake cleaning, check and replace the plugs if not done in 50k, replace the Air Filter, and run a few cans of Seafoam or BK44 cleaner in the tank. I think there is a clogged Cat problem coming, and/or intake carbon that is leading to a bad exhaust gas reading. Is just what I would do.

 

@jgscott , your advice is sound. The upper cleaning, new plugs and air filter, plus MAF cleaning would help, but usually if these are issues, misfire codes (P030x) and MAF codes are also thrown with the CAT codes.

I had both codes on my Gen3 GS, plus misfire and MAF codes. Didn't have any exhaust leaks, did your recommendations, but one CAT code, P0420, would eventually come back. The solution was replacing the downstream HO2 sensor. If the HO2 sensor gets contaminated (maybe from poor/incomplete combustion or carbon fouling), the reading could be outside the normal range, based on where the A/F sensor is running. They work together and have ranges based on where the other reads. The final solution to keeping the P0420 from coming back, was replacing the HO2 sensor for that bank.

@120k miles, carbon build up could be part of the problem. My original recommendation was to make sure he checked the easy stuff 1st, before looking at replacing CATS.

 

Anything is possible. The Codes by the book when it comes to Oxygen sensor are never that straight forward. The Sensor's themselves failing are hardly ever both the P0420 and P0430. Especially going on and off. Most times when they fail due to +/- milliamps vales out, or whatever is when they go they go, not stop and start. If lots is going on dirty I guess you could have contaminated sensors but Not the norm.

If its the Cats, that's $1500 aftermarket to $2500 incl labor to replace. All I said was "if it was me", what I would do that sometimes works if you do it before the Cats clog so bad that you can't do anything but replace them. I would also clean the MAF, because it can cause a incorrect afr mixture too.

I've seen these codes and someone who says "I replaced the Sensor and still have the codes on Toyota/Lexus" many times, especially when it's both codes. Again anything is possible, and I could be wrong but...... its what I would do quick.

 

Might not be too helpful, but the RR Racing tune may help with those codes specifically....

 

ahem, the old spark plug non fouler trick can help eliminate P0420: https://www.autozone.com/ignition-tu...K&newYmme=true

 

I haven't had this set-up fail yet....

 

Is that a pic of a 4th Gen GS HO2 sensor? Doesn't appear to be an OEM (Denso).

You cannot install a spacer like that on a 3rd Gen GS due to the frame rail...too tight. You even need a Toyota specific HO2 sensor installation tool due to the limited clearance.

 

They sell 90degree ones also.


The problem here is this. That 2nd set of sensors also trims a/f and other back to the ecu. Yes the sensor will not detect but you also will not get optimal reading for the ECU to optimize the engine performance. Deleting the waring light in a Tune would still allow the ECU to tune correctly.

 

I went with the last option......

 

This is a good point! I've yet to take care of the problem since I got caught up in a separate project (BMW Rear Subframe Restoration). But the car doesn't feel any different. It's been a while but the code seems to come up after 100 +- 50 miles. I'll place the car on ramps today to take a quick picture of the exhaust flanges right before the downstream O2 sensors. Since the car has over 129k miles, and it has lived its life upstate NY it seems a little rusted and it seems like the gaskets could be due for a change in the next year. One that note I've noticed the following:

The tips of the exhaust have a bit of soot build up. This may have been exacerbated because my girlfriend was using my car over the winter and she drove very short distances (~5 min) causing:
1) The engine and cats not to heat up properly
2) A richer, more carbon rich exhaust

 

All,
Quick update.
I ended up using Cataclean fuel additive as a final hope of fixing the P0430 light, since my inspection and registration was up... and it worked.
I've driven the car over 500 miles since I applied the additive and no lights or stored codes have shown up. I'm guessing the cause of this was carbon buildup.. and the next steps would be to sort out the cause of this buildup.. it could be bad driving habits, wrong use of fuel, a combination of intake and exhaust sensor values that causes the engine to run rich. I'll probably end up using Toyota Techstream to get a closer look at the values the sensors are outputting.

I appreciate the previous replies suggesting the actions I could take.