P0420 Code Attack Method Review

[ejthomp]

Hello all. I've done a search and read up on this code, I'm just bouncing this off you for backup.

Here is the situation: 1996 Camry 2.2L 185,000 miles Runs great, idles fine, starts fine, gas mileage is good. The CEL is on and the code is P0420 - Catalyst System Efficiency Below Threshold Bank 1

I've had this car for 10 years now and it has been gold. The oxygen sensors and catalytic converter have never been touched so obviously it is time.....

I do all of my own auto maintenance and repair. Decent supply of tools, but diagnosing can be difficult. I really don't mind throwing parts at something because I figure I'm either fixing the problem or doing preventative maintenance. Either way, I'm way ahead of bringing it to a "professional".

Here is my plan of attack for this code:

1) Replace Upstream O2 sensor and see if problem goes away
2) Replace Catalytic Converter
3) Replace Downstream 02 sensor

Sound reasonable? Since the OEM parts lasted this long, I plan to use OEM replacement parts.

[Hajoca]

Seems like a 'lazy' or tired after cat sensor.

It may be cheaper to organize the plan as

#3, then drive a few hundred miles and see.

[ejthomp]

You know.... that does make more sense since the car runs fine.

So my attack plan should be:

1) Downsteam O2 sensor
2) catalytic converter
3) Upstream O2 sensor

[ghettosled]

i second what ejthomp said. its the downstream sensor that would send off the 0420 CEL. be prepared for it not want to be removed. mine was a b!tch to remove.

[Hajoca]

I borrowed an acetylene plumbing torch (B-tank) to heat my sensor up till it was cherry red, then loosened it.

I am not sure if PB Plaster and time (re apply and drive a few times) would work for this type of connection.

I used a 22mm Box end wrench.

[ShawnM]

Its just a weak converter. Of course it probably wouldnt hurt to change both O2 sensors anyway. The cars computer is comparing the upstream and downstream sensor patterns to each other in order to determine the condition of the catalyst. It is extreemly rare for a down stream sensor to stick in a high reading. nine times out of ten its just a weak catalyst, which is common at much lower milage than what you have on the original one.

[ejthomp]

So, then I need a new catalytic converter... probably very likely too.

So... $125 for each sensor and $400 for the converter.

Over $600 in parts if I want to do it right..... hmm... tough to swallow, but that is probably what needs to be done. I'll probably have a shop change the converter as that is so much easier on a lift with a torch, etc.

Today, I'm going to remove the upstream O2 sensor and look at it, clean it, and reinstall. I'll clear the codes and verify that the P0420 code comes right back.

[ghettosled]

where are you getting your prices? i picked up my sensor from oxygensensors.com for about $90 and my converter on ebay (made by catco) for about $200. i even replaced the secondary cat with the flex pipe (also made by catco) for an additional $125. everything bolted right up, minus the stock heat shield.

[ejthomp]

I stopped at the local Toyota stealership and they want $160 for each O2 sensor. I found them online for $123 each. The website you led me to has the same things for $90 and $50.... Assuming they really are OEM.... I want less expensive, but I want to only do it once.... I'll pay more for the best quality and easiest installation.

The catalytic converter now confuses me.

I have a front and a rear converter? Which one do I replace first? The front is $300 and the back is $170????

My easy fix plan is getting more complicated.

[Hajoca]

I also have bought Denso sensors from oxygensensors.com and was happy with them, I bought 2 without connectors and did my own connections.

[ShawnM]

The front or main converter is the one you want to replace. The rear or secondary converter is not monitered by the computer.
The Denso oxygen sensor part numbers should be 234-2058 for the front/upstream and 234-2008 for the rear/downstream.
Bosal is another option for an aftermarket converter. The part number is 099-859 if you want to do a search on it.

[JohnGD]

1) Replace Downstream 02 sensor
2) Replace Upstream O2 sensor and see if problem goes away

And read the following article before doing #3:

http://www.motor.com/magazine/pdfs/012009_02.pdf

3) Replace Catalytic Converter

Originally Posted by ejthomp

Here is my plan of attack for this code:

1) Replace Upstream O2 sensor and see if problem goes away
2) Replace Catalytic Converter
3) Replace Downstream 02 sensor

Sound reasonable? Since the OEM parts lasted this long, I plan to use OEM replacement parts.

[ghettosled]

Originally Posted by ejthomp

The website you led me to has the same things for $90 and $50.... Assuming they really are OEM.... I want less expensive, but I want to only do it once.... I'll pay more for the best quality and easiest installation.

The catalytic converter now confuses me.

I have a front and a rear converter? Which one do I replace first? The front is $300 and the back is $170????

My easy fix plan is getting more complicated.

on the site i posted, the sensors show if they can simply be plugged in or if they have to be wired in. i opted for the direct plug in to save the slight hassle.

like others have said, the first and larger one connected to the exhaust manifold is the one that is monitored. the only reason to replace the secondary is if the flex pipe section has rusted though.

also some food for thought - take care of removing the old cat converter; they are actually worth some money. you can probably get about $50 for it in good shape. reason being some companies can extract the precious metals that are inside them, but only if the honeycomb inside is intact.

[ejthomp]

I want to thank you all for educating me.

I just got lucky..... I decided to clean the upstream O2 sensor as a first step just because....Why not? It is easy to do and free.

I disconnected the battery, removed the sensor, sprayed it with carb cleaner, scrubbed it a bit, sprayed it with more carb cleaner and reinstalled it. Reconnected the battery, totally expecting the code to come right back and .......nothing!!!

This morning I took the car down to the DMV emissions testing and it passed!

I'm doubtful this easy, free fix will last long, but I'm ready to take care of it when it does.

THANKS GUYS!

My only theory on why this worked is that a couple weeks prior to the code showing up, I did a throttle body cleaning and maybe I pushed some dirt through that clogged or set the O2 sensor off. I had reset the code once before and it came right back, so I thought I was in for some work.

EASY AND FREE..... How often does that happen in auto repair?

We'll see how long it lasts.

[JohnGD]

Excellent results. I would have thought solvents would certainly kill the sensor.

I guess I'll just clean the daylights out of the next one up the driveway.

Originally Posted by ejthomp

I disconnected the battery, removed the sensor, sprayed it with carb cleaner, scrubbed it a bit, sprayed it with more carb cleaner and reinstalled it. Reconnected the battery, totally expecting the code to come right back and .......nothing!!!