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2007 Toyota Highlander Base - P0420 Code

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Jan 8, 2021, 1:19 PM

Post #1 of 2 (570 views)
2007 Toyota Highlander Base - P0420 Code Sign In

Vehicle: 2007 Toyota Highlander 4-cylinder base model, automatic transmission, 155k miles

Primary Code: P0420 (Catalyst System Efficiency Below Threshold (Bank 1)

Background: My check engine, VSC, & Trac lights all came on. After some work, I ended up replacing the O2 sensor behind the CAT (B1S2) without any luck. Now I am trying to figure out if I should get a new CAT or if I need to replace the B1S1 O2 sensor or A/F sensor. I suppose it could also be something completely different.

Attached Videos: I attached a OBD2 scan tool and recorded the O2 sensors (both) as I drove [video 1 & 2] and as the car was idling after my drive and I tried accelerating [video 3]. All videos below.

Not Captured on Video: I did not record the screen on my scan tool during the cold start but the O2S B1S1 was around 3.2V and fluctuated a tiny bit & the O2S B1S2 was consistently at 0.1V.

What do you think the issue is and why? I would love to know if there could be other things I should look into before dropping some loot on a new CAT or O2 sensor. Thanks!!

Video 1:

Video 2:

Video 3:

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 8, 2021, 1:48 PM

Post #2 of 2 (558 views)
Re: 2007 Toyota Highlander Base - P0420 Code Sign In

It doesn't matter what you scan tool captured. It's not capable of capturing what the computer looks for to set that code.

Here are the most common cause of that code in order.

1) Bad Catalytic converter 90%
2) Lazy 0/2 sensors 5%
3) Exhaust leak upstream of the downstream 0/2 sensor. 5%


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

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