Catalytic Converter?

[ottogaus]

Have CEL on with P0420 on beloved 98 Avy w/215k miles. Garage told me, without doing full diagnostic, that the catalytic converter is bad. What are the chances that an O2 sensor is the problem? If cat needs to be replaced, OEM part alone is about $1,400. Mechanic at the garage suggested a $300 cat and said I would get at least 3 years out of it. True?? Any help greatly appreciated!

[BMR]

Chances are pretty good it's just the O2 sensor, not the cat. Doing the complete diagnostic to determine which is bad is worth the trouble. But if you're gonna throw parts at it, I'd say replace the downstream O2 sensor first. It's cheaper than a cat, and more likely the cause of the P0420.

[TOYOPARTSMAN]

If you go with OEM parts, I do sell Genuine Toyota OEM parts to members for 30% off MSRP. I only charge actual shipping costs plus $2.00 for handling, etc.

[ottogaus]

Thanks BMR. Will definitely check the O2 sensor. When you say the downstream one, do you mean the one underneath the car or one of the two in the engine compartment?? Any way to check the O2 sensor(s) myself? Resistance measurement??

[ottogaus]

Ok - know that the downstream O2 sensor is the one underneath the car. Have had two garages tell me the problem is the catalytic converter and not an O2 sensor since only the P0420 code is being thrown. Help please. Is there a way to test O2 sensors other than just replacing them? Really hoping I don't have to replace the cat given the signicant expense.

[BMR]

Sorry, I missed your post from yesterday.

Yes, there is a resistance check that can be done on the O2 sensor's heating element. But if that were the problem, your mechanics are correct in that there would be another code thrown, specifically a P0141.

What they should do (and may have already done) is hook up an OBD II diagnostic system & monitor all the O2 sensors while it's running for proper function. A P0420 code means the downstream O2 sensor is not detecting any reduction in O2 after the exhaust stream passes thru the cat. It does this by comparing with the upstream O2 sensors. So things like exhaust leaks & marginally bad O2 sensors can trip a P0420 even tho the cat is OK. A proper diagnosis is essential.

[ottogaus]

Thanks again BMR. I may just replace the downstream O2 sensor to see if that fixes the problem. Appears, however, that it is a pain to change. Have you ever changed it by simply crawling under the car? Any tricks to doing so?? Also, I have read that the connector is either under the drivers seat or front passenger seat. Can you tell me which and exactly where underneath the seat it is located and how to disconnect. Many thanks!

[BMR]

Yeah, it's not the easiest. Here's a DIY thread showing how it's done on a V6 Camry, which should be very close if not identical. The driver's seat has to be removed to get access to the connector.

[TedL]

It's under passenger seat on a 99 Avy. 98???????? Look where the wire goes through floorpan.

[BMR]

Good thinkin' Ted. I assumed it was on the same side as on a Camry; bad idea. Before pulling out the driver's seat, it would be best to follow the wire from the sensor to see which side it goes to.