P0420 and P0171

[4runnerWiniarski23]

Hey guys I keep getting a recurring 420 code. Followed by a 171 days later. I checked my maf today because it's quick and easy. Wires look brand new no issue there.

My next logic step is rear O2 sensor. I have a code reader and can see if it's working correctly. It does seem to be switching between lean and rich (high and low voltages)

What else should I be looking into?
Thanks in advance. Also painted my wheels with some duplicolor graphite and red toyota symbols.

My number 1 helper just turned 1!

Sent from my SAMSUNG-SM-G920A using Tapatalk

 

[gamefreakgc]

Congrats on the little one! Mine is 10 months so not far behind you!

On your 4Runner, do you have 1 or 2 catalytic converters?

The P0420 is only 1 of 3 probable causes, ranked most likely to least:

1. Rear O2 sensor failure.
2. Rear (or only) Catalytic converter failure
3. Exhaust leak downstream of the first O2 sensor.

Finding an exhaust leak is not hard to do, you'll hear it first and then you can find it by locating the "puff" of air pulsing through. Don't burn yourself. If you don't hear anything strange, replace the rear O2 sensor.

On to the P0171:

1. Vacuum leak. Check your hoses for cracking or disconnected parts. Did you do any engine work just prior to the P0171? They take a day or two to pop up usually, I think it's a 2 instance CEL like the P0420.
2. Dirty MAF. I know you checked for integrity, but spray some carb cleaner or MAF sensor cleaner on both wires, if it's a 96-98 then spray it down the center of the turbine. Make sure it dries COMPLETELY with the turbine design before installing.
3. Failed front O2 sensor. If this is the case, you might have some problems with your emissions causing both sensors to fail.
4. Failed MAF. If you have the 99-02 sensor, you can get a cheap test replacement for $13 on Amazon. Not a long-term solution but helps with troubleshooting since a brand new DENSO sensor is $70-$80.

 

[PanamaCity2002]

Just had this happen. Any of this fix it?