Catalyst Efficiency Below threshold - TCCoA Forums
 
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post #1 of 8 (permalink) Old 11-03-2007, 11:46 AM Thread Starter
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Catalyst Efficiency Below threshold

Well the other day I finally changed my front passenger O2 sensor cause it was bad, and have the torn up knuckles to show for it. Reset the computer and everything was good. Just got my windows tinted and was enjoying a little drive when it comes back up. Had it scanned and it said Catalyst Eff. Below Threshold, Bank 2. I remember this code came up before and went away for a long time.

Should I change the rear drivers o2 sensor or could it be a bad cat? I still have the same power as I have had, Its showing no symptoms of a bad cat.

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post #2 of 8 (permalink) Old 11-03-2007, 09:26 PM
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its the drivers side upper sensor, bank 2 is drivers side, bank 1 is passenger side

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post #3 of 8 (permalink) Old 11-04-2007, 02:28 AM
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Quote:
Originally Posted by Chris_Murder View Post
its the drivers side upper sensor, bank 2 is drivers side, bank 1 is passenger side
That is incorrect. The code for catalyst efficiency is the result of the reading of the rear/lower oxygen sensor, not the front/upper. The original poster is correct in pinpointing the rear sensor on the driver's side in connection with this DTC.

Gcline, there is a chance that the code is the result of the oxygen sensor not reading correctly, but it's not a good one. Generally the catalyst efficiency codes are spot on. Despite this, it might still be prudent and cost-effective (in relation to replacing the catalytic converter) to replace the rear sensor, especially if they have a lot of mileage on them, there has been any kind of exhaust contamination (i.e. antifreeze), or if the wiring/connectors aren't in good shape.

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post #4 of 8 (permalink) Old 11-04-2007, 10:40 AM
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A set of mil eliminators and a piece of rebar fixes the cats problem real nice...as long as your state doesn't have inspections.

A really bad o2 sensor in the second position will cause errors on the whole circuit; I just had to replace one over this issue; put the new one in the first position, moved that one to the second position, no more problems. It was giving a circuit failure error...

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post #5 of 8 (permalink) Old 11-04-2007, 11:33 AM Thread Starter
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I really dont feel like dishin out 60-70 bucks a piece for the rear sensors. would the cheaper ones be ok for the rear ones? I think I remember master486 saying that they were a while back on another thread...

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post #6 of 8 (permalink) Old 11-04-2007, 12:14 PM Thread Starter
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Edit:

Well I was outside so I figured Id check it out. I can hear it rattling now. Looks like im gonna have to invest in some new converters. AutoZone sells the the whole thing, all 3 converters for like 300 bucks, might just end up with that.

1997 Mercury Cougar XR7 Sport 4.6L
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post #7 of 8 (permalink) Old 11-04-2007, 10:57 PM
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beware..of AUTOZONE parts some things just don't last.....be carefull!!!
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post #8 of 8 (permalink) Old 11-05-2007, 07:42 AM
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For new cats, go on ebay and you can pick up some high flow cats for about $50/each and take them to an exhaust shop and have them welded in.

If you want to make 100% sure its the cats before you buy anything, hook up a computer and look at the current data readings for the o2 sensors. What you should see is sensor 1 on both banks going back and forth between .100V and .900V, and sensor 2 on both banks should be staying right around .450-.500V. If you see the reading on sensor 2 behaving like sensor 1, then you need cats. If it stays steady around .5 and then drops out to 0 or almost 0 all of a sudden, then comes back up to .5, then replace the O2 sensor.

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