99 Mystique Issue

[Dr. Apex]

My roommate has a 99 Mystique V6 that has the MIL light on, codes P0420 and P0174. The car has 81k miles. The shop he saw simply want to replace the cats on the car at a cost of $1000. Apparantly the cats are built into the manifolds on this car?? From what I read though the P0420 may be caused by the system running too lean somewhere overloading the cats and causing the rotten egg smell hes getting.

 

Couple suggestions I picked up are to try and run a strong fuel system cleaner thru it and if the cats are dirty to try possibly laquer thinner in the fuel system to clean that out??

 

I'm no mechanic but am trying to help him as he knows nothing about cars and don't want to see him get ripped off. Suggestions where to start looking and some cheap remedies before he goes to a shop again to drop $1k on a car worth only $2k???

 

TIA, Ben

[copperhead]

http://ezinearticles.com/?P0171-and-P0174-Codes---Dont-Replace-an-Oxygen-Sensor-Before-Reading-This&id=1865946

 

http://www.p0420.com/

 

I'm no mechanic either but I'd think that if both banks are saying its lean then its probably lean, not two bad cats. I don't see how a cat goes bad at all, let alone at 81k. According to those links I'd say look for a vacuum link. Also clean the MAF. I'd toss in new plugs as well just because, and go with strictly OEM spec.

[SinisterSS]

1st there could be a PCM update to correct the issue, take it to a dealer and have it checked, if the car has the latest software then check for vacuum leaks, possible intake gasket leak since those are the most common issues on that car with those code. If he has access to a decent OBD scan tool watch the o2 activity 1 or more may have a problem(bad o2 sensors can cause a CAT to fail)