My 98 Sienna with 120,000 miles is facing a smog renewal in California. The check engine light is on, with an error code of P0240 = catalytic convertor low efficiency. The dealer service says the OBDII is smart enough to detect a bad O2 sensor, and the cause is more likely to be a bad catalytic convertor.
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Dealer says the cat. is integrated with the two exhaust downpipes, and they're quoting $1300 just for the part (Toyota #17410-0A120). Are there aftermarket options for this? Is this a DIY job (I have tools, patience, and minimum skills)?
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Thanks for suggestions; I'm new at sourcing Toyota parts, since this is this first major failure.