Trouble Code P0420

My scanner says "System efficiency below threshold"
my Chiltons book says "catalyst efficiency monitor and/or exhaust system
fault" for that code.

Could it be the Oxygen Sensor? I have 70K on this one

TIA

Mr. Whatever wrote:
> My scanner says "System efficiency below threshold"
> my Chiltons book says "catalyst efficiency monitor and/or exhaust system
> fault" for that code.
>
> Could it be the Oxygen Sensor? I have 70K on this one
>
> TIA
Doh... found an archive post that suggests it's probably oxygen sensor.
I forgot to mention I have 96 Explorer 4.0 4WD AT. I see in manual that
there are 4 sensors. Should I replace all 4 if one is bad? TIAA

Mr. Whatever wrote:
> Mr. Whatever wrote:
>
>> My scanner says "System efficiency below threshold"
>> my Chiltons book says "catalyst efficiency monitor and/or exhaust
>> system fault" for that code.
>>
>> Could it be the Oxygen Sensor? I have 70K on this one
>>
>> TIA
>
> Doh... found an archive post that suggests it's probably oxygen sensor.
> I forgot to mention I have 96 Explorer 4.0 4WD AT. I see in manual that
> there are 4 sensors. Should I replace all 4 if one is bad? TIAA

Double Doh. Found another post that suggested having the PCM re
calibrated or reset first. Something about the trouble code being stored
in memory. It cost $90 but the trouble code hasnt come back after 200
miles. Seems like an inherent flaw like that should have been paid for
by the factory. Oh well, Kragen said they would take the 02 sensors back.

How many miles did you have on when you did this?

This code came up on mine also. I did do the cat replacement, as my mileage
was high, and I haven't had the
code come on again. I haven't had my PCM recalibrated. Anyone know what
that's all about? Is this a dealer only type thing requiring special
equipment?

Paul

"Mr. Whatever" > wrote in message
m...
> Mr. Whatever wrote:
>> Mr. Whatever wrote:
>>
>>> My scanner says "System efficiency below threshold"
>>> my Chiltons book says "catalyst efficiency monitor and/or exhaust system
>>> fault" for that code.
>>>
>>> Could it be the Oxygen Sensor? I have 70K on this one
>>>
>>> TIA
>>
>> Doh... found an archive post that suggests it's probably oxygen sensor.
>> I forgot to mention I have 96 Explorer 4.0 4WD AT. I see in manual that
>> there are 4 sensors. Should I replace all 4 if one is bad? TIAA
>
> Double Doh. Found another post that suggested having the PCM re calibrated
> or reset first. Something about the trouble code being stored in memory.
> It cost $90 but the trouble code hasnt come back after 200 miles. Seems
> like an inherent flaw like that should have been paid for by the factory.
> Oh well, Kragen said they would take the 02 sensors back.

Paul Scrutton wrote:
> How many miles did you have on when you did this?
>
> This code came up on mine also. I did do the cat replacement, as my mileage
> was high, and I haven't had the
> code come on again. I haven't had my PCM recalibrated. Anyone know what
> that's all about? Is this a dealer only type thing requiring special
> equipment?
>
> Paul
>
I had 67K+ on it when the trouble code came up. As far as I know only
the dealer can flash/recalibrate/reset the PCM but I'm not certain. I
found the post about the PCM at http://www.ford-trucks.com/forums

Haven't seen the post on your link. If it is referring to power programmers
and chips, all these do is modify the spark and fuel curves as well as the
rpm limits. They do nothing to the operating strategy that decides when to
set the MIL and send a DTC to memory. In the past, Ford (along with most
other marques) have approached the EPA for permission to alter the fault
determination strategies to reduce the incidence of "nuisance" MILs.

Dealers are the only ones with this sort of programming data. The original
poster would have to go to the dealership and have his car connected to the
WDS to determine if a later flash is available for the car.


"Mr. Whatever" > wrote in message
m...
>
> Paul Scrutton wrote:
> > How many miles did you have on when you did this?
> >
> > This code came up on mine also. I did do the cat replacement, as my
mileage
> > was high, and I haven't had the
> > code come on again. I haven't had my PCM recalibrated. Anyone know what
> > that's all about? Is this a dealer only type thing requiring special
> > equipment?
> >
> > Paul
> >
> I had 67K+ on it when the trouble code came up. As far as I know only
> the dealer can flash/recalibrate/reset the PCM but I'm not certain. I
> found the post about the PCM at http://www.ford-trucks.com/forums