During stop and go driving, I get P0420 check engine light code for bank 1. Feeling bummed of the possibility that I might need to replace my cats. Wishful thinking that I hope if it might be the O2 sensor instead.

I do have Techstream though to help diagnosis. Does anyone know how to use Techstream to monitor the RPMs, fuel trims, O2 sensors with engine live data to isolate the root cause?

Other observations, I also have some cylinder 5, 7 misfires showing on Techstream. I inspected my Bank 1 spark plugs this past weekend and it appears that a couple were ash fouled (fuel rich?) and one was oil fouled. I also had cracked tube seals and had a couple of inches of oil in my spark plug tubes.

If I can't isolate whether it is the O2 sensor or Cat Converter using Techstream, I thought I would just change O2 sensor first with Denso, change out the spark plug tube seals and spark plugs (3473) and hope that clears the P0420.

Any help and advice would be appreciated. Thanks, Jeff

 

Does your engine burn oil?

 

Oil in the plug hole is indicative of valley plate oil leak. Gotta fix that as well as tube seals. You need to check bank 2 plugs as well. The o2 sensor may be bad. If you're burning oil the cats may need cleaning or replacement. Tell us the year and mileage please.

 

I would definitely fix the tube seals first.

 

I believe, you meant spark plug tube grommets need to be replaced.

 

2007 LS460L, 168K miles. I bought it this summer from the second owner who did very minimal maintenance (Oil changes - 10K+) for 3 years.

I'm not sure of the oil consumption yet. I think it is burning some oil but not sure how much yet. I had the oil change when I first got the car 4K miles ago. However, I misread the dipstick one morning a month ago (it looked dry to me) and added about a quart of oil. I'm remissed that I didn't wait to some time between incremental pours and definitely put in too much oil because it was probably still near full.

After a long drive, I checked my engine and my dip stick had a stream of caked on oil on the yellow handle and the dip stick reading was slightly higher than full. The Lexus dealer (recent drain and fill transmission) noted that I had oil all over my undercovers and suggested a blue dye test to find the leakage points. My dip stick is currently right at the full mark so I need to watch it going forward.

Prior to overfilling the oil, techstream was reporting no misfires. After overfilling, I do have misfires with 3 spark plugs along bank 1 and very minimal misfires on #6 on bank 2. I'm worried that I might have damage some of the seals in the engine.

I bought new tube seals and spark plugs from Bell Lexus (yet to arrive). They have their annual big Xmas sale and got a good deal on spark plugs. Denso 3473 for $11 bucks each.

Where would you guys buy the Denso O2 sensor? Worried about fakes.

 

Regarding your original question, here's an overview of Techstream from the TIS website. You're looking for the Data List function for the ECU you want to monitor. You can select which parameters you want displayed and can record data over time. Should make it relatively easy to do some driving and see what comes up.

I've also attached the FSM section for code P0420 and how to track it down; hopefully that points you in the right direction.

If they have it, RockAuto has been dependable enough for me. They sell a ton of crap parts as well, but if you specifically match the brand and part number you should be okay. Amazon seems to be where fakes are most prevalent, along with eBay.

 

Service Manual gives a clear indication on how to determine if the Catalyst is comprised.

Just a visual for those who haven't seen Techstream. My O2 Sensor is reacting to the micro changes to active test - fuel mix (rich and lean).

Thanks Trogdor113 for the service manual files. Very helpful! Techstream diagnosis is showing that my catalytic converter is bad or there is an exhaust leak. I'm planning on doing a soapy water test later this week for checking for holes in the exhaust. Since it is just around $60, I might just change out the O2 sensor eventually to fully confirm that the catalytic converter is bad. I don't need to CA smog until Oct 2023 so I have time to work through this.

 

Glad to hear it helped! I don't envy your future O2 sensor replacement...

 

Is this the screen that comes up when you choose the active test? I've been dealing with a P0420 for since it first started getting cold and I've run the graph just to see what the AFS and O2 sensors are doing but I haven't run the active test yet. On the regular graph it does not show the micro changes in the wave length like in your screenshot.