2004 Toyota 4Runner Catalytoc Converter

  • 6 CYL
  • 4WD
  • 101,000 MILES
Got the ODBII code 0420 indicating a bad catalytic onverter. Everything I have read indicates the 2004 4Runner 6 cyl has 2 catalytic converters. A local reapi shop told me that there are actualy 4. The cat is supposed to be between the 2 oxygen sensors, correct? When I look at the cats to buy online, they are the pipes and parts AFTER the second oxygen sensor. Any advice?
Do you
have the same problem?
Tuesday, December 23rd, 2008 AT 2:24 PM

1 Reply

First of all, I would stay away from that local repair shop. Obviously they have not done exhaust work to realize how many cats go to a vehicle. You have two catalytic converters, and the one that is giving you trouble is cat#1, the one on the passenger side.


Before you purchase, read this description of the trouble code.

P0420 OBD-II Trouble Code Technical Description

Catalyst System Efficiency Below Threshold (Bank 1)

What does that mean?

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.


You will likely not notice any drivability problems, although there may be symptoms.


A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions

Some suggested steps for troubleshooting a P0420 code include:

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

*** I would call Toyota and find out about the extended warranty ***
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Saturday, December 27th, 2008 AT 4:09 AM

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