2012 Post DIY Valley Cooling Plate Repair CEL P0420 (1 Viewer)

[Tommy Argh]

Looking for some expert help here. I tackled the VCPL job myself following the write up here. Since finishing the job I almost immediately acquired the P0420 error code. I’ve been chasing down the issue with no luck. I did replace the EGR gaskets, PCV valve, and intake gaskets while I had it apart. The engine runs normal idle and driving. Once it reaches operation temp and about 15-20 mins in it trips the CEL. Anyone encounter this code after doing the job? Could there be a leak from the EGR cooler

 

[Acrad]

Wonder if wiring to upstream O2 sensor has an issue?

Air Fuel & Oxygen Sensor (O2) / Problems / Questions / Concerns - ClubLexus - Lexus Forum Discussion - https://www.clublexus.com/forums/gx-2nd-gen-2010-present/887771-air-fuel-and-oxygen-sensor-o2-problems-questions-concerns.html#post11115422

 

[Tommy Argh]

Wonder if wiring to upstream O2 sensor has an issue?

Air Fuel & Oxygen Sensor (O2) / Problems / Questions / Concerns - ClubLexus - Lexus Forum Discussion - https://www.clublexus.com/forums/gx-2nd-gen-2010-present/887771-air-fuel-and-oxygen-sensor-o2-problems-questions-concerns.html#post11115422

View attachment 3150466

As in wiring harness leading up to the plug before the sensor?

 

[Tommy Argh]

Wonder if wiring to upstream O2 sensor has an issue?

Air Fuel & Oxygen Sensor (O2) / Problems / Questions / Concerns - ClubLexus - Lexus Forum Discussion - https://www.clublexus.com/forums/gx-2nd-gen-2010-present/887771-air-fuel-and-oxygen-sensor-o2-problems-questions-concerns.html#post11115422

View attachment 3150466

As in wiring harness leading up to the plug before the sensor

 

[Acrad]

Possible but you may also need to leverage Techstream as well.

 

[Acrad]

 

[Tommy Argh]

View attachment 3150596View attachment 3150597

Thanks very much for the info. I’ll try my best to follow protocol but I’m no expert. I was able to watch the graph of the scanner of b1s2 and it appeared to act funny.

 

[Tommy Argh]

Update 10/28/22: I cleared all the codes and took it for another spin to trigger the CEL for the data. I watched the freeze frame data and it appears that Bank 1 sensor 1 voltage spikes to 1.xx. After inspection of said sensor I noticed that it had a slight coating of dried coolant. My first intuition, replace the sensor. After a few hours with plenty of breaks in between and a few different parts store runs for various o2 sensor tools I got it replaced. I drove it home for the weekend to get it to cycle. Last night the CEL came back on but this time the code is P2195, telling me the sensor I just fought with is bad…

 

[Rednexus]

It's possible the connector itself or wiring upstream of the connector may be damaged (or possibly full of caked coolant). I would inspect as much of the harness as possible to look for signs of damage, in addition to inspecting the connector. If the harness upstream of the connector is OK, and the connector is questionable or looks fine, I would consider cutting off the connector and just hard wiring the O2 sensor to the harness via some heat shrink crimp connectors (you can always splice a new connector back in later). A connector can have a issue inside of it that is not obvious from the outside.

 

[Tommy Argh]

It's possible the connector itself or wiring upstream of the connector may be damaged (or possibly full of caked coolant). I would inspect as much of the harness as possible to look for signs of damage, in addition to inspecting the connector. If the harness upstream of the connector is OK, and the connector is questionable or looks fine, I would consider cutting off the connector and just hard wiring the O2 sensor to the harness via some heat shrink crimp connectors (you can always splice a new connector back in later). A connector can have a issue inside of it that is not obvious from the outside.

If I’m not mistaken and correct me if I’m wrong but I think the leads for the upstream are in that bundle of harness that’s bolted to the backside of the intake. That harness was a PITA to get unbolted and un-clipped in order to get the intake manifold off. I’m wondering if I may have damaged wiring in that process.
I currently don’t have access to Techstream. Could someone please screen shot the P2195 diagnoses and maybe how to test the pins for Bank 1 Sensor 1 upstream connector pretty please?!

 

[Acrad]

 

[Acrad]

 

[Tommy Argh]

@Acrad thank you a bazillion!

 

[Rednexus]

If I’m not mistaken and correct me if I’m wrong but I think the leads for the upstream are in that bundle of harness that’s bolted to the backside of the intake. That harness was a PITA to get unbolted and un-clipped in order to get the intake manifold off. I’m wondering if I may have damaged wiring in that process.
I currently don’t have access to Techstream. Could someone please screen shot the P2195 diagnoses and maybe how to test the pins for Bank 1 Sensor 1 upstream connector pretty please?!

You certainly could have damaged the wiring in that area, but it's also very common to have the connector between the main harness and O2 sensor damaged, especially if it had coolant dripping onto it (the inside of the connector could have a bad connection due to the coolant). I would at least investigate that before diving into inspecting the rest of the harness, as it's the lowest-hanging fruit for this issue.

 

[Tommy Argh]

You certainly could have damaged the wiring in that area, but it's also very common to have the connector between the main harness and O2 sensor damaged, especially if it had coolant dripping onto it (the inside of the connector could have a bad connection due to the coolant). I would at least investigate that before diving into inspecting the rest of the harness, as it's the lowest-hanging fruit for this issue.

I’ll test that first. Thank you.

 

[Tommy Argh]

I was able to get back to the rig and pull some data this afternoon from the Freeze Frame. I’ll link that video:
I was also able to test the upstream sensor unplugged from the harness. I could only pull readings from the top two terminals. The vehicle was off.

I was able to get the vehicle side of the harness up into to the engine bay for a better inspection of the wires and it’s plug. Nothing seemed out of the ordinary to my untrained eye and again I was only able to pull measurements from the top two terminals. The vehicle was switched to the on position, not running, with the CELs still on the dash.

Maybe you gentlemen can help me make some sense of this?

 

[Tommy Argh]

I got to tinkering around with the rig again. I found that bank 1 sensor 1 didn’t go in straight when I replaced it not allowing it to sit flush or seat correctly.

From what I’ve read this is a very common thing from any factory as they just run them down. That would explain why it was such a PITA to remove. Ended up retapping those threads, 18mm x 1.5, and had to bend a few custom wrenches to get that job done. The good news is that P2195 is gone, for now, but P0420 has reappeared. I was attempting to graph sensors 1 and 2 to see if in fact the rear cat is bad but my scanner ran out of battery and the cable is at work. I’ll have to start fresh come Monday. Hope everyone’s having a good weekend.

 

[Tommy Argh]

Eager to bring some resolution to what seems like a never ending battle I dove directly into finding an exhaust leak. I switched the hose around on the shop vac and taped the hose in the tailpipe forcing air back up towards the engine. I sprayed soapy water on all major exhaust connections that were accessible. Low and behold I found two almost immediately. One at the left Y pipe, after the cat, and another in the center after both Y pipes have met.

Could this be the culprit for the P0420 code?
I decided to watch more data on the scanner and I noticed that b1s2 heater was pegged with no movement while b2s2 fluctuated as if normal. Is the sensor measuring rich? What can be the cause of that? Im stumped. Any help would be highly appreciated!

 

[Rednexus]

Both of those exhaust leaks are behind the rear O2 sensors, so they should not throw a PO420 code. However, a leak ahead of the rear O2 sensors (such as at the midpipe to exhaust manifolds) could throw a PO420 code, so it's worth it to spray some soapy water there to see if you have a leak. My gut feel is that you have a wiring or connector issue somewhere, either on the upstream or downstream sensors, but I'm not familliar enough with reading the O2 graphs to be able to confirm it.

FWIW my GX has had leaks at both of those joints. The midpipe joint (ahead of the Y) was rust-welded together and I had to cut out the flange and re-weld in a new one (didn't come out the best). The Y-pipe to catback leak isn't too bad to repair with a new Toyota donut gasket.

 

[Acrad]

How goes the battle?