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Code P0420 problem

E

erb13

CEG'er
Joined
Aug 30, 2002
Messages
36
The CEL came on about 4 months ago on my 1998 CSVT. I reset the code P0420 twice and the CEL with same code came back on in about one month each time. No other codes have ever been shown. I have also noticed about a 10% mileage drop (24 to 22 MPG) during this time but no other driveablility or power loss problems. Other info:

Both upstream O2 sensors replaced about one year ago
Car has 76,000 miles and is totally stock
Original plugs and wires
I do not know if the PCM has been reprogrammed for the original narrow range for this code. The car and I are currently living in Europe and I do not know if the local Ford dealer can reprogram a US PCM

Using Autotap software I have graphed the upstream and downstream O2 sensors and the voltage readings coincide about 2/3 of the time.

Is there any other data from the Autotap software I could use to determine the real problem? Any other items I could look at or simple things I could to to assist the troubleshooting? I do not want to replace the pre-cat due to the expense for a 9 year old vehicle and I have read and heard this code is in may cases a false reading or is caused by another problem.

Eric
 
You might not really have a problem. False cat effeciency codes are common on V6 Contiques. I'll explain.

The PCM includes a cat monitor. The cat monitor runs ocassionally, only when certain conditions have been met. It is the last of several intermittant monitors to run. If the monitors have not completed, you will get a P1000 code showing that the drive cycle has not been completed.

The cat monitor compares the switching rate of the upstream oxygen sensor to its matching downstream oxygen sensor. If the cat is effecient, the downstream oxygen sensor will switch mutch slower. If the switching rate too closely matches, the cat monitor goes "tilt" and sets either the P0420 or P0430 code depending on which bank is indicating a possible problem.

The next step in determining if you have a problem is to get the cats hot and using a scanning device see if the real time readings show the upstream and downstream sensors switching in lock step with each other. YOU MUST MAKE SURE THE CATS ARE GOOD AND HOT. If there is a reasonable varience then you should be fine. If so, reset the PCM and don't worry about it.

After about the third year of ownership, the cat effeciency codes would ocassionally set on my car. The time between would vary from six months to two years. The car has always passed an emissions test with extremely (near 0) low numbers.

If indead you do have a cat that is not working well, sometimes they can be revived by running some cleaner through the engine either as a vacuum suck cleaning or by using injector cleaner in the tank or both accompanied with some spirited driving to get the cats hot to burn off any coating that may get in the way.

Let us know what you find.
 
I live on a small island and have very few chances to drive the car for any length where the engine and exhaust get hot for an extended period. I will try the injector cleaner in the tank for a couple of tanks, run in a lower gear and see if that helps the problem. I appreicate the info.

Eric
 
I live on Terceira Island, part of the Azores Islands which belong to Portugal. The Azores are about 900 miles west of the coast of Portugal in the middle of the Atlantic Ocean. I work at Lajes Field for the US Air Force.

Eric
 
erb13 said:
I live on Terceira Island, part of the Azores Islands which belong to Portugal. The Azores are about 900 miles west of the coast of Portugal in the middle of the Atlantic Ocean.
Click to expand...
I remember the Azores! Bob Hope was supposed to land there maybe 15 years ago to do a stint for the USO but could not due to high winds. He ended up doing his "stand up" broadcasting from the plane he was in. :cool:
 
Score one for Berryman's. I put a bottle in with a half tank of gas and just before I filled up the CEL went off and has stayed off for another 100 miles. I guess cleaning the injectors and pre-cats worked for me.

Eric
 
Let us know if it comes back on. I am running STP fuel injector cleaner (black bottle) through mine and the light hasnt come back on either. Will see in time if this works or not.
 
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