Chico6

So at 126K miles, the check engine light (and the VSC Trac lights) all lit for the second time since I have owned my 2002 4Runner SR5. I had the code read at Autozone and it was P0420. I looked up the code online and followed the advice of some of the forum members (like Big Balls McFalls). I replaced the original heated oxygen sensor (the one located after the catalytic converters) with a new Denso. After driving around several times (about 60 miles after installation), the check engine light (and VSC Trac lights) have finally quit lighting up. I hope those lights don't come back for long time (hopefully till I am able to get a new 4Runner later this year or next).

Here are some things that might be helpful:
I used a large 7/8" wrench to remove and install the sensor (I recommend using the ring-end of the wrench, but first disconnect the sensor connector and pass it through the ring-end of the wrench in order to be able to get to the sensor's hex head). The old sensor was tight, but eventually broke loose after several tries (and a little WD40).

I measured the resistance (Ohms) of the original (old) sensor and it was 12.9 Ohms. The new sensor reading was 15.7 Ohms. According to the specs, the resistance of a good sensor should be between 11-16 ohms (measured at 68 F) and between 23-32 Ohms (measured at 1472 F). I am assuming my old sensor was not to spec. at the higher temperature range.

I looked up the oxygen sensor part number from the Denso Website (http://www.densoaftermarket.com/catalog/) and then searched around online for the best price.

Amazon.com (cost $64, no tax, free shipping) had the best deal and the sensor arrived brand new, sealed in plastic bag along with a small tube of anti-seize lubricant. The new sensor is identical to the original (old) Toyota/Denso sensor.

Also, I did not notice any change in the engine's performance during the time that the Check Engine Light was On. Even with the new sensor installed, I have not noticed any changes.

Hope that helps.

okie81

Thanks for the feedback Chico Amazon had the best deal I could find on the front O2 sensor as well

TheDurk

The fact that the sensor passes a resistance test does NOT mean the sensor is good. It just means the heater filament circuit is functional. If it FAILS the test, it is bad for sure, though. In fact, a bad heater will probably throw other codes than P0420.

Changing the rear sensor should not affect performance, nor should performance degrade due to a P0420. The rear sensor only sets codes, it does not affect operation.

In case others are wondering, the hex-type sensors were only on '01 and '02, I believe.

Nelsonmd

Ah, that's what I was guessing.

Chico6

Since installing the new oxygen sensor, I have noticed that the mpg has improved (from 18mpg to about 21mpg). Also, the Check Engine light has not returned.

mt_goat

Yeah I've heard that from others too. I don't see why, but apparently the ECU goes into some kind of safe mode or altered fuel map when the P0420 code is thrown. The 420 code is the cat/cats not functioning up to spec code so making the truck run richer seems strange to me, but what ever.