Catalytic converter

Have '02 4wd crewcab tacoma w/116,000 miles. Check engine light came on, error code: P0420. Firestone mechanic indicates needs front & rear catalytic converters replaced, determined by upstream & downstream oxygen sensor content. Now check light is no longer on. Has the truck healed itself? So here are my questions:
Had 2 bids for cat convertor: one for $825 (unless run into problems w/?stuck studs; also 2 year warrantee); 2nd for $991 (Firestone–1 yr warrantee). Both of these will use ?direct fit cat convertor. Toyota Dealership quoted around $3000!! What is wisest course of action?
2nd question: Firestone recommended new spark plugs, new battery/battery corrosion package & fuel injection flush. How often do spark plugs & batteries typically need to be replaced? Had new spark plugs in 2011; new battery in '08.

Thanks very much for your help!!

  1. Run away from Firestone and find a trusted independent mechanic using the “Mechanics Files” tab on this site.

  2. Do NOT allow anyone to talk you into replacing the cats unless it has been absolutely proven they are bad, which I very much doubt, after only 116k miles. And the check engine light went off. Something else is going on, and a good mechanic will figure it out. Firestone just wants to sell you expensive parts.

  3. Your owners manual should say how often to replace spark plugs. Conventional plugs should last 40k miles or so.

  4. Batteries are usually good for 5 years or so. They can go longer but you Increase risk of getting stranded in winter. If the battery is still cranking well, it’ll probably last the summer. Get a new one on sale in the fall when the weather starts to turn cold.

Actually, the CEL can go on and off intermittantly when a catalytic converter gets marginal as the operating conditions change with normal operation. It isn’t at all unusual. The truck hasn’t healed itself, but the converter is on the “cusp” of its efficieny going below threshold totally. Depending on what kind of driving you do, yours may well ne there after 11 years and 116,000 miles. This is not at all unusual for a Toyota.

Based on the quotes, I assume this is a 4 cylinder engine? Go with the aftermarket direct-fit quotes. They’re just as good as the OEM parts. Dealers commonly charge two to three times the price of private shops using aftermarket parts. As long as you use a reputable shop, you’ll be fine.

You can fiddle-fart around with this until the cows come home, but based on my experience with Toyotas you’ll end up getting a new converter in the end. And likely a new upstream O2 sensor as well.

I would at least try replacing both O2 sensors first before going whole-hog and replacing the cats, if there’s a chance it’s a sensor problem and not a cat problem. Especially if you’re going to have to replace the upstream sensor anyway.

What @jesmed said - it might be the cat(s), but it’s much more common for an O2 sensor to be bad, and much cheaper to replace. And yes, run away from the Firestone shop for this kind of diagnosis and work.

There are tests a good mechanic can/should run to determine if it’s the cat or the an O2 sensor. Most of the time it’s an O2 sensor.

As for Firestone. The mechanics work on commission. So I’d be leery of their diagnosis. Get a second opinion.

BTW, I had an '02 Tacoma and an O2 sensor went bad on me at something like 50k miles.

Google ‘Toyota P0420 causes’, you’ll find out there are several, besides a bad cat:

•Leaded fuel was used where unleaded was called for
•A damaged or failed oxygen sensor
•Downstream oxygen sensor wiring damaged or connected improperly
•The engine coolant temperature sensor is not working properly
•Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
•Retarded spark timing
•The oxygen sensors in front and behind the converter are reporting too similar of readings
•Leaking fuel injector or high fuel pressure
•Cylinder misfire
•Oil contamination

A mechanic needs to evaluate these before deciding on the repair.

PS–when I had the bad O2 sensor on my Tacoma, I believe the code I got was also P0420, and the problem was solved by replacing the downstream sensor. I’ll bet you have the same problem: bad downstream O2 sensor.