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Oxygen Sensor Green


96wWindstar180K
06-24-2007, 11:09 AM
I just finished my lower intake manifold gaskets. Im waiting 1 oil change in between before sending another sample to Blackstone Labs. I decided to pull my upstream oxygen sensor bank 1. (Im still getting P0420.) As Wiswin mentioned before it might be green from antifreeze. Could this sensor be reading slow or wrong and causing P0420? I did a vacume test to check for back pressure of the converter and it responds well. The van runs well but the code still comes. I was planning on replacing the converter but now im not sure. I guess a new sensor or maybe the upstream and downstream would be cheaper then the converter. Any thoughts? Thanks

wiswind
06-25-2007, 09:29 PM
P0420 is catalyst efficiency below threshold for Bank #1
Bank #1 is the rear bank of cylinders (bank #1 contains cylinder #1 on most all vehicles).
This would be the reading from the oxygen sensor after the catalytic converter for the rear bank of cylinders.

On my '96, the rear most catalytic converter has the "downstream" oxygen sensor mounted into the body of the converter.....and it broke right out with VERY little turning only force........which would have been a problem had I not been changing the converters anyhow. (due to rattling insides)

The 2 converters are part of the "Y" pipe assembly.
When I checked, the list price for the FORD replacement part was about $1600.
I found it online for just over $1200 at the cheapest.
I bought a Walker "direct fit" replacement for about $321
I have read that aftermarket converters are not as good as factory original, but that Walker is about the best of the aftermarket replacements.
The Walker "direct fit" replacement is the whole assemlby, 2 converters, and the pipes to the 2 exhaust manifolds......and the 2 pipes that merge into 1 that end just in front of the flex pipe.
Mine has been fine for about the past 3 years.

If you change this assembly, use a wire to hold the front part of the flex pipe up.....as the flex parts can be damaged if left to dangle.

I did NOT enjoy this job...very dirty, and 1 stuck exhaust manifold bolt (broke, ended up getting a new replacement one from the dealer for $5).

96wWindstar180K
06-25-2007, 11:11 PM
wiswind
Do you think I could be recieving the P0420 because the sensor is damaged? Im not sure the converter is bad I did a vacume test and all seems well. What do you think about just changing both oxygen sensors bank 1?

wiswind
06-27-2007, 07:35 PM
I would try switching the downstream sensors from bank to bank......except for the issue that I mentioned about the one that is mounted into the body of the converter........and I had that problem with very little turning only force.....with a oxygen sensor socket.....and the threads had been soaked hours ahead of time with PBlaster.

If you switch the downstream sensors between banks and the problem moves to Bank #2, then you can figure that the downstream sensor (at this point on bank #2) is defective.
If the code comes back on bank #1, then the problem is with the converter.
If you have a broken wire, etc with the sensor circuit, you should get a different code.

I personally would not worry about the upstream sensors at this point.
If you have the urge to replace an upstream sensor, I would replace BOTH upstream sensors as a pair.....so that you will have the same switching charactoristics between the 2 banks.
As an oxygen sensor ages, the switching charactoristics change (slow down).
Don't worry about it...as the PCM monitors the switching rate, and will set a code stating specifically that the switching is too slow if that happens.
But in changing just 1 sensor, you most likely will end up with different switching charactoristics between the 2 banks.....which most likely will not cause major problems...but I am guessing that the most optimal performance will be with a very close match.
I changed my upstream oxygen sensors and noticed no difference in engine performance or economy.....and that was at about 170K miles on the original sensors.
Also, I recommend you get the Motorcraft brand (I got mine from Rock Auto).
The reason being.......they may be manufactured by Bosch, but they are manufactured to Motorcraft Specifications.
The extra cost is very small.....unlike the $1200+ versus $321 for OEM versus aftermarket for the converter "Y" pipe unit.

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