Sunday, April 15, 2012

Repairing 2001 Toyota Sienna Check Engine Light Code P0420

When we bought our 2001 Toyota Sienna in 2011 the check engine light was off. But on the way home from the dealer the light came on. We came to know that the van had a long history regarding that code. I guess the dealer had reset the computer before we did the test drive. I guess that's why they say to bring used cars to a mechanic for inspection. I didn't know anything about OBD (on-board diagnostics) at the time. Learned a lot since then.

It was a long road to fixing the problem because I had to learn a lot along the way. The things I tried:

1. Bought an OBD reader and reset the computer then took it in for emissions test. Haha, yeah, nice try. They can't test the car if the tests read 'not ready'.

2. There was a Toyota bulletin out about how there was a known problem with the ECU:

Technical Service BULLETIN October 19, 2005 "M.I.L. “ON” DTC P0420 – EG047-05"

So I got a good deal on the computer from Gary at Toyota of Newnan: http://www.toyotaofnewnan.com/Department-Parts.aspx.

Unfortunately that didn't fix the problem.

3. I could see in the vehicle history reports that one shop had recommended the computer replacement (~$1500) and another had recommended replacing the catalytic converter and O2 sensor (~$2000)!

So I took the van to the local Toyota dealer to see what they recommended. For $65 they tested and suggested I replace the catalytic converter and O2 sensor. Estimate for repair about $2500 including tax. Yipes!

So I reviewed my Haynes book, found online Toyota maintenance manual (image below) and did research on the internet to see how to replace the CAT. I could purchase both warm up three-way catalytic converters (WU-TWC) and the catalytic converter itself for about $900 so that could be big savings.

I worked up the courage to try the replacement myself and ordered the parts from www.autopartswarehouse.com with only a few weeks to spare before we had to pass the emissions test in order to keep the registration current.

The parts arrived within a couple weeks and the gaskets were included, so I didn't need the ones I had purchased from the local www.oreillyauto.com store. One tip: be very careful when ordering the exhaust pipes - some may be listed as 'direct fit' but will also have text indicating that some minor welding will be required. I couldn't use the bank two WU-TWC pipe because it needed welding/modification. Here's the two pipes I did replace. Notice that the new pipe in front on the left is much more basic that the OEM part on the right:

But not being able to use that third pipe saved me $350 actually because replacing just these two pipes above (the bank 1 WU-TWC and TWC), plus the O2 sensor did the trick!

Summary
If I could do this over again, I would:

1. Replace just the TWC pipe and see if that alone fixes the problem. ~$250
  • I used autopartswarehouse.com Eastern Catalytic Converter part number EAST40432
2. If not, I'd then replace the post-cat O2 sensor also and see if that fixes the problem. ~$100
  • I bought that at the local O'Reilly

Note: when replacing the O2 sensor you do not need to remove the passenger seat. Just unscrew the left-side plastic panel around the base of the front passenger seat. That gave me enough access to unclip the original O2 sensor wire and clip in the new one. Saved a lot of time!

You might be able to go even cheaper if you have welding equipment. You could hacksaw the old TWC out and weld in a generic replacement. The generics appear to be about $100.

I drove the van up onto ramps and large flat bricks to make room to work underneath. Please be super safe about that. I was on a concrete pad so it was pretty solid.

Here's what the old O2 sensor looked like. It may still have been working ok, I didn't have time to check.

Hope that helps someone!

14 comments:

Anonymous said...

Thanks for the detailed descriptions and pics. Best info. I've gotten so far on the problem.

Drod said...

I'm facing a very similar situation with my 2001 Toyota Siena. Which catalytic converter brand did you install in your van?

Drod said...

I'm facing a very similar situation with my 2001 Toyota Siena. Which catalytic converter brand did you install in your van?

Lars said...

Hi Drod, I added the brand and part number to the Summary section towards the bottom. Hope that helps.

Drod said...

Im coming off a busy week considering that our second child was born today. I'm going to attempt to buy the parts this coming week (twc and rear O2 sensor) and do the work myself (hopefully it won't be too difficult). I'm debating whether or not to also replace the bank 1 warmup twc. My biggest question is how does the p0420 code know that it's the bank 1 warmup twc that is supposedly bad if the rear O2 sensor is after all three converters? Thanks

Lars said...

Drod, that sounds good. I used penetrating oil and was able to remove 3 of the four bolts holding the TWC pipe. I had to hacksaw the fourth bolt. An inexpensive reciprocating saw from Harbor Freight Tools saved some time/effort on that cutting. I think I bought four new bolts at the local O'Reilly. From my experience, I would save the WU-TWCs for next steps if the TWC and sensor don't fix the problem. In my case, I don't think the WU swap helped. It is a good question about how would the code know what's wrong. I think it just narrows down the set of possibilities. The Toyota dealer suggested the TWC and WU-TWC and then the O2 sensor just to be sure (all the components which could be involved in causing the P0420), but I take that with a bit of salt since they make good money selling parts/service. To be fair, I expect they also want the customer to have the problem fixed on the first try. I'm hoping you'll be ok with the TWC and sensor swap like me and save some money/effort. Good luck! By the way, no engine codes for us a year later.

Anonymous said...

Lars, in your original post you mentioned that not using the third pipe saved you $350. Which third pipe are you referring to? The muffler and the tail pipe? Thx for the info.

Anonymous said...

Thanks for all the good and detailed info, especially the how-to for easier sensor replacement. I will have to tackle this project super soon...
It's somewhat frustrating that different brands have different measurements for the center cat (3 way nearest the engine firewall)...one brand says 36"and others say 37" and others don't say anything at all!
Hopefully it doesn't make too much difference.

Anonymous said...

Thank you so much for this information - I too have a 2001 Toyota Sienna van that needed a new catalytic converter. Mechanic quoted me $600 to take off and clean (~60% chance of working) or $2,500 for new catalytic converter (replacing all 3 sections that you detail). Well that was a bit rich for me - I did as you guys instructed and just replace the TWC pipe. (bought the EAST40432 from JC Whitney for ~$180 with free shipping). It did the trick! Only hard part was a couple of rusted bolts - need to buy 1/2 inch socket set (used the 14mm) that was slightly larger than the one I had. Also sprayed rusted bolts with PB Blast the night before I took off. Thank you so much for the detailed diagrams and advice about this - it has really saved me a bundle of CASH! :D

Lars said...

Awesome! Really glad to hear that helped.

Lars said...

My apologies to some of the earlier commenters - I'm sorry I didn't manage to reply. I don't log on here much. I hope your repairs were successful.

john said...

Great write up. I have a 00 avalon with p420 and will try this attempt. Thanks

Anonymous said...

Had to deal with this on my 2006 Sienna. Something I learned along the way points at always trying the TWC only first when you have code P0420. The ECU puts up that code by comparing voltages from the #1 and #2 O2 sensors. The sensors are usually upstream and downstream of the TWC, not the other WU-TWC parts, so I gather the TWC is the most likely culprit. Now that's not what they choose to do at the dealer for different reasons. Since they cannot pinpoint where the problem is any closer than you have so far, they go for the shotgun approach and replace all the parts at once. This way you pay for any extra labor upfront (whether needed or not). It wouldn't be good for their business if they try something that doesn't work and then have to rework it on warranty (labor not chargeable to you). It sucks, but I can see why they do it that way. Also, it probably doesn't make sense to add more sensors for troubleshooting a part that goes bad once in maybe 100K miles, but that is another story.
Leaving this comment here FWIW. Good luck.

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