"scjwonder" <none@000.com> wrote in message
news:1205627_1c9b2d02de687df63fb3c60fe66078ab@auto boardz.com...
> I have a '00 Legacy GT and changed both oxygen sensors after getting a
> Check engine code P0420 (i think) for oxygen sensors. Within a week
> the check engine light is back- same code. Why would new sensors, fore
> and aft not keep that "check engine" light off?
>
> --
> Posted at author's request, using moderated http://www.AutoBoardz.com
> interface
> Thread archive:
> http://www.AutoBoardz.com/Check-engi...ict247877.html

It's because the PO420 code doesn't have anything to do with the O2 sensors
per se. That code sets when the sensors determine through correlation that
the catalytic converter is not doing it's job. If the O2 sensors themselves
have a problem it sets a completely different code(s).

"Dave" <mecdave@hotmail.com> wrote:

>It's because the PO420 code doesn't have anything to do with the O2 sensors
>per se. That code sets when the sensors determine through correlation that
>the catalytic converter is not doing it's job. If the O2 sensors themselves
>have a problem it sets a completely different code(s).

what is the code if it is the O2 sensors themselves?

<me@privacy.net> wrote in message
news:0nd474d6c6e2v79l65ei516ba935d10hn9@4ax.com...
> "Dave" <mecdave@hotmail.com> wrote:
>
>>It's because the PO420 code doesn't have anything to do with the O2
>>sensors
>>per se. That code sets when the sensors determine through correlation that
>>the catalytic converter is not doing it's job. If the O2 sensors
>>themselves
>>have a problem it sets a completely different code(s).
>
> what is the code if it is the O2 sensors themselves?

There are dozens. Here is the largest group...

P0130 O2 Circuit (Bank 1, Sensor 1)
P0131 O2 Circuit Low Voltage (Bank 1, Sensor 1)
P0132 O2 Circuit High Voltage (Bank 1, Sensor 1)
P0133 O2 Circuit Slow Response (Bank 1, Sensor 1)
P0134 O2 Circuit No Activity Detected (Bank 1, Sensor 1)
P0135 O2 Heater Circuit (Bank 1, Sensor 1)
P0136 O2 Circuit (Bank 1, Sensor 2) (See P2270, P2271)
P0137 O2 Circuit Low Voltage (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P0139 O2 Circuit Slow Response (Bank 1, Sensor 2)
P013A O2 Sensor Slow Response - Rich to Lean (Bank 1, Sensor 2)
P013B O2 Sensor Slow Response - Lean to Rich (Bank 1, Sensor 2)
P013C O2 Sensor Slow Response - Rich to Lean (Bank 2, Sensor 2)
P013D O2 Sensor Slow Response - Lean to Rich (Bank 2, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0141 O2 Heater Circuit (Bank 1, Sensor 2)
P0142 O2 Circuit (Bank 1, Sensor 3)
P0143 O2 Circuit Low Voltage (Bank 1, Sensor 3)
P0144 O2 Circuit High Voltage (Bank 1, Sensor 3)
P0145 O2 Circuit Slow Response (Bank 1, Sensor 3)
P0146 O2 Circuit No Activity Detected (Bank 1, Sensor 3)
P0147 O2 Heater Circuit (Bank 1, Sensor 3)
P0150 O2 Circuit (Bank 2, Sensor 1)
P0151 O2 Circuit Low Voltage (Bank 2, Sensor 1)
P0152 O2 Circuit High Voltage (Bank 2, Sensor 1)
P0153 O2 Circuit Slow Response (Bank 2, Sensor 1)
P0154 O2 Circuit No Activity Detected (Bank 2, Sensor 1)
P0155 O2 Heater Circuit (Bank 2, Sensor 1)
P0156 O2 Circuit (Bank 2, Sensor 2) (See P2272, P2273)
P0157 O2 Circuit Low Voltage (Bank 2, Sensor 2)
P0158 O2 Circuit High Voltage (Bank 2, Sensor 2)
P0159 O2 Circuit Slow Response (Bank 2, Sensor 2)
P0160 O2 Circuit No Activity Detected (Bank 2, Sensor 2)
P0161 O2 Heater Circuit (Bank 2, Sensor 2)
P0162 O2 Circuit (Bank 2, Sensor 3)
P0163 O2 Circuit Low Voltage (Bank 2, Sensor 3)
P0164 O2 Circuit High Voltage (Bank 2, Sensor 3)
P0165 O2 Circuit Slow Response (Bank 2, Sensor 3)
P0166 O2 Circuit No Activity Detected (Bank 2, Sensor 3)
P0167 O2 Heater Circuit (Bank 2, Sensor 3)

And here is the group of cat codes...

P0420 Catalyst System Efficiency Below Threshold (Bank 1)
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
P0424 Heated Catalyst Temperature Below Threshold (Bank 1)
P0425 Catalyst Temperature Sensor Circuit (Bank 1, Sensor Circuit 1)
P0426 Catalyst Temperature Sensor Circuit Range/Performance (Bank 1, Sensor
Circuit 1)
P0427 Catalyst Temperature Sensor Circuit Low (Bank 1, Sensor Circuit 1)
P0428 Catalyst Temperature Sensor Circuit High (Bank 1, Sensor Circuit 1)
P0429 Catalyst Heater Control Circuit (Bank 1)
P042A Catalyst Temperature Sensor Circuit (Bank 1, Sensor Circuit 2)
P042B Catalyst Temperature Sensor Circuit Range/Performance (Bank1, Sensor
Circuit 2)
P042C Catalyst Temperature Sensor Circuit Low (Bank 1, Sensor Circuit 2)
P042D Catalyst Temperature Sensor Circuit High (Bank 1, Sensor Circuit 2)