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Discussion Starter · #1 ·
I bought the car with the check engine light on a few months ago.. 96 Z3 1.9l 157,800 miles

The owner said the light had been on for a year or so with the same code P0420
Catalyst System Efficiency Below Threshold (Bank 1)
I have cleared the light several times and its always came back on with the same code.

Today I took my car to Bimmersouth in bogart,ga I was going to check with them and see if they had a used cat.
Aftering talking with the guy at the front, he suggested that I pay to have it scanned with their machine.
The cost of the scan would be applied to the cat and install, if that was the actual problem. So I agreed.

$100 later and they can not find a single fault/code and said that it could of been a hiccup..

My question is how can a cheapo autozone scanner pull up a P0420 and their machine could not?

Has this ever happened to anyone before??
 

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Discussion Starter · #5 ·
some one droped the ball at bimmer south. imo. ...............replacing the cat might not fix the car. there will be a repair tree to follow for that code....o2 sensor,AIR system [if app] etc etc
This is what i am thinking. My plan is to drive the car until the CEL comes back. Buy the downstream O2 and bring it back up there for a free recheck and they said they would install it for free..

If that doesnt do it, then maybe the Cat?? There is no secondary air pump but i guess there could be a small vac leak somewhere:dunno:
 

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I have learned, especially with European, to check both sets of codes : Manufacturer specific and OBD Generic. We, at shops, tend to lean towards Manufacturer specific as they typically give you more information, and may have additional codes to help you pinpoint the source of a Generic code. My guess is they went into the manufacturer side only, and saw no codes. Rare, but it does happen. Cheapo scanner pulls generic codes only. Since the addition of ethanol to the fuel supply, we have seen an excessively high rate of catalytic failures. Post cat O2 sensors rarely fail. Rarely a vacuum leak will trigger an efficiency code, but I have seen it. Didn't know they had finally opened in Bogart. Not a big fan of used cats, but probably a better option to a lot of the aftermarket selections I have experienced.
 

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Discussion Starter · #7 ·

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I have installed a couple of the Magnaflow cats and been very pleased, though they were direct fit with the pipes and flanges. I don't work at a muffler shop and don't claim to be a welder, so I don't install a lot of universal fit cats. I believe you will be ok with the Magnaflow. A lot of the cats that we get through the exhaust wholesalers are, well lets say you get what you pay for. The cheaper brands are typically half the size of OE, have smaller pipes, and are lucky to last 2 years at best. I believe the Magnaflow, installed correctly, will be just fine. Make sure that the engine is tuned and running properly. Rich running burns cats, not lean.
 

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Discussion Starter · #9 ·
Ok sounds good. I just need to find a decent shop that could weld it in, if i have to go that route. I believe that everything is in good running order. I havent pulled the plugs yet but i am getting decent Mpgs.
 

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If you can't find one, PM me and I will send you to a muffler shop in Conyers that I have seen good work come from. They are also a Magnaflow dealer. You may check with them on the price of buying from them installed versus what they charge to install yours.
 

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Discussion Starter · #11 ·
UPDATE:
Replaced the after cat O2 sensor. and the check engine light came back on tonight. Didnt have time to run by my local autozone to pull the code, but my guess is its the P0420.

Now I think my next step is to

1. Find someone who will let me borrow or buy a peake scanner. Maybe this will pull a more specfic code?
2. Replace the cat.

Any Ideas?
 

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Discussion Starter · #12 ·
UPDATE 2: found a good deal on a peake scanner.. Pulled the code and its table 07 fault 28 catalyst efficiency. This is the only code it pulled up..

Tomorrow i am going to check for any vac leaks but i am leaning towards this being a bad cat..
 
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