P0420 Code error on 2006 LC with lots of recent maintenance

[Tx2006LC]

I just had a P0420 code error pop up tonight. I am feeling a bit defeated with all the money I’ve spent and work I’ve had done somewhat lately.

Within the last 4 months I have had a lot of work done to my Land Cruiser

You can see all that was done here:

Thread '2006 Land Cruiser P0330 - Knock Sensor Drama at the Dealer'

Feb 20, 2025

Howdy Ya'll

Long time reader and consumer of these great posts, first time poster.

Looking for some insight on my 2006 Land Cruiser (VVT-i) and a P0330 error.

The Background​

• Check engine light came on, scanned it with BlueDriver, and got P0330 (Knock Sensor 2 - Bank 2).
• Cleared the code a few times, but it kept coming back quickly.
• Noticed a definite loss of power—seems like the ECU is cutting power in failsafe mode.
• Scheduled a diagnostic with Toyota ($185, waived if they do the work).

Dealer’s Diagnosis & Quote...​

• Tx2006LC
• 100 series help needed knock sensor local dealer
• Replies: 39
• Forum: 100-Series Cruisers

New SAI pump, both knock sensors, starter, hoses, and more.

And 2 years ago I had the catalytic converters and back replaced due to these same codes being thrown although it was P0420 and P0430. New O2 sensors were installed as well.


Any thoughts on what my next course of action should be?

Could this be due to using 87 octane and not using 93 octane gas?

 

[Tx2006LC]

Would providing some logs help?

file:///var/mobile/Library/SMS/Attachments/21/01/082439F6-878D-4311-8877-87ADDA16CCFE/DataLog-Oct_23_2025_1-50-29-PM.csv

 

[Tx2006LC]

150 miles later a P0174 code popped up. Then cleared itself.

250 miles after that, the p0174 and P0420 both appeared.

I am wondering if this is spark plug related maybe?

 

[vipergrhd]

150 miles later a P0174 code popped up. Then cleared itself.

250 miles after that, the p0174 and P0420 both appeared.

I am wondering if this is spark plug related maybe?

I would check for exhaust leaks. Check your intake hoses for cracks too.

 

[baltistyle]

If you think it’s due to dirty gas, add some high pea cleaner, like redline or Techron

 

[OEMGUY0720]

When was the last time the AF and O2 sensor were checked physically? And do you have an OBD scanner that has voltage readouts for the upstream (AF) sensors and downstream (O2) sensors?

 

[Tx2006LC]

If you think it’s due to dirty gas, add some high pea cleaner, like redline or Techron

I will try this.

I will pick up some Techron and put it in the next tank.

That being said, I put in a tank of 93 octane and the codes cleared in less than 50 miles. I might try running a tank of 87 again to see if that causes the codes to fire again.

I have also read some conflicting articles about pumping more gas into the tank after the initial pump shutoff. Is there any truth to these claims that over filling by a gallon will damage o2 sensors or Catalytic converters?

 

[Tx2006LC]

I would check for exhaust leaks. Check your intake hoses for cracks too.

Thank you! I can do this. Although I’ve never really done this before. Can you give me some additional guidance on what to do and what I should be looking for or listening for?

 

[Tx2006LC]

When was the last time the AF and O2 sensor were checked physically? And do you have an OBD scanner that has voltage readouts for the upstream (AF) sensors and downstream (O2) sensors?

Thank you.

I haven’t check the o2 sensors they were installed and h haven’t check the AF sensor. Can you give me advice on where these are located and what I should be looking for?

I have a blue driver. Let me see if I have voltage readouts as a part of the live stream of data. Any advice or guidance you can provide would be great. Happy to look into this and report back

 

[baltistyle]

I will try this.

I will pick up some Techron and put it in the next tank.

That being said, I put in a tank of 93 octane and the codes cleared in less than 50 miles. I might try running a tank of 87 again to see if that causes the codes to fire again.

I have also read some conflicting articles about pumping more gas into the tank after the initial pump shutoff. Is there any truth to these claims that over filling by a gallon will damage o2 sensors or Catalytic converters?

Not Cats or Sensors, but the charcoal overflow canister. It's meant for vapor and not liquid. It can cause starting issues but that can be researched elsewhere.

87 is not inherently dirty. Try to find a local station that sells "top tier" branded gas. This will ensure it's a higher quality for the octane chosen. Then again, these trucks can eats strait sand and oil out in the Mid East. Sounds like a bunch of bad gas but Techron is cheap.