Catalyst system - code P0430

Tiny
IAN MEACOM
  • MEMBER
  • 2003 FORD TAURUS
  • 6.0L
  • V6
  • FWD
  • AUTOMATIC
  • 99,300 MILES
I have already replaced the bank two O2 sensors and my check engine light has been on for weeks. I used my scan tool in live data mode to check the voltage and short/long term fuel trim levels and everything seems to be right except my short term fuel trim for bank two sensor two. It is reading at 99.2 and is not fluctuating while driving like everything else with the O2 Sensors. I have no idea what might be causing that number to be so high. Any help would be greatly appreciated!
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Wednesday, April 12th, 2017 AT 2:30 PM

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Tiny
CARADIODOC
  • EXPERT
P0430 - Catalyst System Efficiency Below Threshold (Bank 2)

There are no fuel trim numbers for the downstream oxygen sensors. Fuel metering is not their function. The upstream sensors should change between "rich and "lean" about two times per second. If their average indicates a more-rich or more-lean condition, that is when the Engine Computer adjusts the fuel / air mixture, and it does that constantly while you're driving. Those are the short-term fuel trim numbers.

There is a base line the computer starts at when calculating fuel delivery. When it sees it is always making the same short-term adjustments, it gradually moves the amount of correction to the long-term fuel trim. The next time you start the engine, the computer uses those new long-term numbers as the starting point, then it needs to readjust the short-term numbers less. A different way of saying that is the short-term numbers refer to the adjustments needed right now, and the long-term adjustments are the average of what has been needed over time.

The rear oxygen sensors simply look at the exhaust gas after it has been cleaned up by the catalytic converters. If the converter is working, that rear sensor's readings will switch between "rich" and "lean" perhaps once each minute or two. If the converter is not cleaning up the exhaust gas, since no change is taking place, the rear sensor will change state at the same rate as the front sensor. That is how the computer knows to set the "converter efficiency" fault codes. Where many people get confused is those efficiency codes can only be set from the readings from properly-working oxygen sensors. Replacing the sensors does not fix the problem.

Catalytic converters do not fail too often on their own. The most common cause for a failure is too much unburned gas is burning inside it, typically from a spark-related misfire, then the catalyst melts or becomes contaminated. The fix for code 430 is to replace the converter, but then I would watch the front oxygen sensor's readings closely to be sure it''s switching properly, and the fuel trim numbers are low. If the short-term numbers are high negative, there is too much unburned hydrocarbons in the exhaust, and the computer is trying to reduce that.
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Wednesday, April 12th, 2017 AT 3:52 PM
Tiny
IAN MEACOM
  • MEMBER
Thank you! I had a feeling that number 99.2 represented something else. So then the solution would be to replace the bank 2 converter and perhaps the bank 1 o2 sensors as well? So what you are saying is for me to get that efficiency reading means the o2 sensors are functioning properly. Also, what exactly does the number 99.2 represent?
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Wednesday, April 12th, 2017 AT 4:07 PM
Tiny
CARADIODOC
  • EXPERT
I do not know what that number is for. As a guess, I would suggest it might be the actual percent of efficiency, but I have never seen that before. If that is what it is, I would not know if it means that is the percentage used up or that is left. What do you get for the bank 1 reading?

I am more familiar with scanner readings for Chrysler products, which are very similar to GM's and many other manufacturer's products. Ford always likes to do things differently, and that includes how their data is retrieved and displayed. Some of their systems work the same way, but you would never know it from trying to interpret the data.
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Wednesday, April 12th, 2017 AT 6:57 PM

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