On the return leg of a ~1300mi roadtrip, my 2008 LR3 4.4 threw a P0420 code (catalyst efficiency below threshold, bank1). It happened just after getting back on the interstate following a quick stop (non-fuel). The previous hour was spent at sustained 80-90mph speeds (Western Idaho). My wife was driving so I spend some time looking at the IIDTool and taking a log of the O2 sensors. Also cleared the code and it never came back after several more hours of freeway driving.

Initial observations: At speed, the fuel trims were all very healthy. I didn't log them, but +/-3.0 or below on all four. Bank 1, Sensor 2 O2 is definitely cycling as compared to Bank 2, Sensor 2 which was steady around 0.5/0.6V. Attached chart shows this.



The truck has always run well and continues to do so, but I'm pondering what actions I might take in response to this finding to avoid potentially destroying my bank 1 cat or getting into a situation where this code is a more regular occurrence. Some history: Bought the truck April 2017 at 135k, currently has 145k. I replaced spark plugs and cleaned TB and MAF at 136k. New PCV valve last year (preventative). Couple cans of Jectron cleaner in the tank recently. I have the dealer history which shows an interesting entry at 97k in late 2013. Codes P0420,P0133,P0116-24. Dealer replaced the bank 1 converter, upstream o2 sensor, and coolant temp sensor ($1900, glad it wasn't me paying).

So if the bank 1 cat is truly going again, whatever was the root cause may not have been addressed. After reading up on it, here are a few things I was thinking about doing: (1) clean TB again, check how oily it has gotten in 9k miles. (2) check EGR for clogs/carbon build up (3) take more data logs under conditions that more closely match my regular driving (mix of in town and highway closer to 60-70mph rather than 80-90) and (4) use a can of cataclean or similar product to clean the converter.

Any other thoughts or suggestions?

TIA,
-Dan

 

This page was linked in a post from my searches. Very helpful: https://www.discountconverter.com/ca...rter-&News=120

 

Was this a code that came up you saw live or did this actually trip the CE light?

 

Tripped the light. Also, the data posted above was taken after the light had been cleared (and didn't return). So even though the post-cat sensor was continuing to cycle rather than stay steady like bank 2, it was apparently below the threshold to trip the light.

 

Sometime seems very odd. I would continue testing. What I don't get is why Bank 1 O2 downstream was not replaced post cat replacement. Sure, you should replace the upstream with a new cat. But seeing as downstream are not terribly expensive you would think it would have been replaced too. My only thought is downstream sensor is giving false data. Only testing by you can determine that.

 

On a 800 mile trip last fall I was down to 60 miles left in tank. Stopped on Oklahoma, bought premium gas with no alcohol. Wife starts driving and about 30 minutes later .....CEL. Stopped, checked code. P0420 I thought it was the gas, cleared code drove home. Never had it come back since.

I never investigated further. I think it would have to come back every week for 4 months before I would spend $1900 to fix it since there is no drivability problem. I had this issue on my 2007 HSE and a bottle of mr gasket catylic converter cleaner made it go away for about 3-4 months. Car was flooded before I resolved the issue.

I am interested to know the cause since every rover I own is a ticking CEL waiting to happen.

Jeff

 

Dakota: I don't really suspect the downstream sensor since it is cycling. Don't they usually fail lazy? That said I won't discount it as I continue to investigate, thanks for the response.

Jeff: Now, maybe we're onto something! I had been driving pretty much the whole trip and this code was within the first 10m my wife was behind the wheel, hah. I'd generally agree that an occasional code without other issues might be ignored, but I'm inclined to press on this one a bit for the following reasons- (1) the recorded data substantiates the code (2) we have emissions testing where I live and (3) from my research a variety of issues may degrade the cat over time if not addressed. So if there is something to fix, it may be worth the effort now vs. later.

I drove a few short trips yesterday, basically just enough to get the engine coolant to operating temp. For these trips, downstream o2 sensors on each bank were cycling and in close agreement with each other. I don't think the cats achieved operating temp. I'd like to get a capture this weekend that adds catalyst temp, and shows a drive starting from cold all the way up to sustained freeway speeds. Will post back.

 

This is great information. I literally have the exact same truck as you... just clocked 145,000 yesterday. I had the same code come up on mine after returning from a ~400 mile trip doing about 60-80 mph about 2 weeks ago. I’ve since cleared the code and it hasn’t returned. I’ve recently replaced the EGR Valve, MAF Sensor, PCV Valve, spark plugs, ran a can of BG44K and cleaned the throttle body. The truck has been running great, but I have been noticing really poor fuel economy in the city (granted Seattle streets only let you go about 15-20mph... ). Would love to hear what solutions you do find as I don’t really want to spend $2,000 or more.

 

Definitely seems to be a trend of seeing the catalyst efficiency codes associated with longer highway trips. Mtaylo32, did you do that work before or after seeing the code?

I'd be interested to see other data captures from trucks that have and have not popped these codes. The four pids above are all that is needed, and steady state highway seems to be the most relevant time to take data. It's easy to log and export a CSV with Gap IIDTool, but also possible with much less expensive tools. I've also been using OBDFusion ($10 iOS, Android available) along with a $30 Veepeak bluetooth OBD device ( ). It doesn't give you any LR-specific capability, but a great generic diagnostic tool with log and dashboard ability.

Anyway, if folks want to post some captures here please do. I can graph your CSV if needed.

 

I did the work before the code popped up. My truck had an extreme fluctuating RPM problem which members said is associated with the MAF and PCV so I popped those out and did the spark plugs at the same time. The truck idles and runs smoothly since. I've now been seeing RPM fluctuations when I shift the truck into park from drive, which is probably a different issue altogether. I've cleaned my throttle body about 3 times since purchasing ~2 years ago (not sure how often you should clean the TB). Trying to get my hands on an IID Tool to get some more information. I've probably driven about 3,000 miles since doing that work I mentioned before. The indy shop in town mentioned swapping the purge valve next.