PO420 code fixed on 1998 V6 4Runner

[AZRunnin]

I know there are other posts on here about this but I wanted post my experience in case it helps someone else diagnose/fix their truck.

CEL was on. Took it to the dealership and they said it needed a new catalytic converter and sensors and it would cost $2,730. Umm, no thanks.

Took it to a cat shop (Mad Hatter in Phoenix who are great btw) who said the cat was fine but something was causing the cat to get hot (based on its color) and that same thing is likely causing the CEL.

Code was PO42 which AutoZone said probably causes include:

1. Air leak in exhaust before rear O2 sensor
2. MAF sensor
3. Fuel system fault
4. Faultly catalytic converter

I tried the following:

1. Cleaned the MAF - did not help
2. Bought a used MAF on eBay for $35 - did not help (returned it less $5 restocking fee)
3. Replaced the rear O2 sensor - this fixed CEL

The 02 Sensor was $45 on Amazon. 2 bolts and a plug, no need to jack the truck up, and I replaced the sensor in 10 minutes. I used PB Blaster on the bolts the day before and I also have no rust or corrosion (AZ truck).

Super easy DIY and sure beats $2,730 at the dealership.

The rear O2 Sensor i used was Denso 234-4154 from Amazon. This is on a 1998 4Runner V6 4WD SR5.

 

[Road Bull]

I have the same situation with my 2002 4ruuner. This was my next course of action. I am glad to hear that the 02 sensor replacement fixed it.

 

[AZRunnin]

If your MAF sensor is clean I would try the O2 sensor.

Good luck.

 

[MONTYMTB]

I have the same situation with my 2002 4ruuner. This was my next course of action. I am glad to hear that the 02 sensor replacement fixed it.

If you don't know, you will need a different part number for your '02:
Amazon.com: Denso 234-4261 Oxygen Sensor: Automotive

 

[AZ4Running]

Thats the dealership for you. I am a mechainc and i know first hand that dealer techs only plug in and read codes then shot gun repair and oem cats and o2 sensors are pricey. A fast simple way to check a cat is to measure the temp of the pipe going in and coming out after then engine is warmed up. A good working cat will be 200-300F hotter at the outlet min 150F hotter. The rear o2 sensor works by sensing the difference in air between itself and the front o2 sensor(s) if the rear sensor is slow or going bad then it can cause a po420 code. Many people just want to put on a new cat but that is not always the problem, cats do go bad though. Hope that all makes sense. Bad kitty bad kitty my pot pie

 

[Road Bull]

If you don't know, you will need a different part number for your '02:
Amazon.com: Denso 234-4261 Oxygen Sensor: Automotive

Just ordered mine. It should be here Friday from Amazon. This will give me something to do on the weekend. Hell, I might take off my running boards too.

 

[AZBub]

I wasn't so lucky, ended up having to get a cat. Got a magnaflow unit. Kind of like the rumble under acceleration. I was really hoping for an O2 fail instead though.

 

[MONTYMTB]

Just ordered mine. It should be here Friday from Amazon. This will give me something to do on the weekend. Hell, I might take off my running boards too.

Little install tip that worked really well for me when I helped a buddy replace his: use a 22mm combo wrench - you can disconnect the old one and the clip will fit through the closed end of the wrench. You won't get many turns at once, but worked better than anything else I tried.

 

[cek77]

Love to hear a success story! most people post the problem and we never get the final solution.

Since you guys are tossing around part numbers, what is the Amazon rear O2 for a '97 v6 4x4 auto? There are quite a few for sale on Amazon and I wasn't sure which one to get.

 

[MONTYMTB]

Love to hear a success story! most people post the problem and we never get the final solution.

Since you guys are tossing around part numbers, what is the Amazon rear O2 for a '97 v6 4x4 auto? There are quite a few for sale on Amazon and I wasn't sure which one to get.

Should be the same one linked to in the first post of this thread.