P0420 Catalyst System Efficiency Below Threshold (Bank 1)

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Hello all,

I have a '95 Eclipse GST with 86k miles and my "check engine" light came on recently. I took it to my local dealership and got back a OBD code of P0420 (Catalyst System Efficiency Below Threshold (Bank 1) ). He recommended replacing the rear O2 sensor --AND-- the converter ($1369).

My questions are: Shouldn't the dealer know if it's just the rear O2 sensor by doing some diagnostic tests-- thus saving me +$1000 dollars? Or would he definately know it's the converter, and if so, why is he suggesting replacing the rear sensor as well? I just want to make sure everything is on the up and up...

Oh, and also: He asked me if I planned on keeping the car for long, and I said not if it keeps costing me this much to run it. Then he said I probably should not get it fixed because it's only going to get worse. You think he's being sincere, or is this just a way to get me from going elsewhere to find a cheaper solution?


posted by  xj220

wow i love guess and check technicians. its either the rear o2 or cat crapped out.. highly unlikeyly both. but yea replacing both will fix your problems.

although he should suggest to u to check the cat first. i didnt know cats were that expensive.

posted by  thongsai

Thanks for your reply.

Yeah, this a-hole dealership has gotten the better of me before, so I'm much more cautious of their "solutions" now. I only take it to them because they're the only Mitsu dealer around for miles.

One time, I took in for service for brakes, and they told me the battery died (without warning)-- wanted to charge me $150 to replace it. I went to Sears, bought a $59 battery and I replaced the damn thing myself at the dealer's lot. During another service they said my headlights were oxidizing and wanted to charge me $540-- PER HEADLIGHT to replace! I ordered them on the Internet for $169 per headlight. So yeah, I doubt the cat really costs much to replace.

Ok, enough venting. Time to find an good, honest tech in the area...

posted by  xj220

You can test an O2 sensor with a propane torch and voltmeter. Pick up the special socket at a parts store or something. How many miles does this thing have?

posted by  PeteC

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