Changed O2 Sensors - Now P0430 and P0420 Codes - Why?

[Mark]

A friend, recently had her O2 sensors replaced for 1996 DiscoI. I think the miles on her Rover is around 110,000.

After the O2 sensors were replaced, the P0430&P0420 codes were thrown. I went into the passenger footwell and removed the Emissions module which cleared the "Red", Service Engine Soon. Then I cleared the codes.

She drove it home that afternoon from work and made several trips around town with multiple starts/stops. This morning on the drive to work, the "Amber -Check Engine" light came on.

I checked the codes and P0430/P0420 returned.

My thoughts are all of the following:

a. The O2 sensors were not compressed completely into the cat pipes.
b. A leak simultaneously in the cats
c. The manifold is leaking ...
d. Wrong O2 sensors, she ordered the "Black" plugs and not the Gray plugs like my 1998 Disco.

Now, under what conditions, could both sides of the Cats throw codes after changing out the O2 Sensors.

 

[healey1006]

I suppose she might have gotten the wrong O2 sensors. I googled the PO420 and came up with this:

What does that mean?Basically this means that the oxygen sensor downstream (after) the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

SymptomsYou will likely not notice any drivability problems, although there may be symptoms.

CausesA code P0420 may mean that one or more of the following has happened:

Leaded fuel was used where unleaded was called for
An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged exhaust manifold / catalytic converter / exhaust pipe
******** spark timing
Possible SolutionsThe simplest thing to do is to reset the code and see if it comes back.

Next step is to measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). The voltage should be low and steady (~200mV, depends on the vehicle). If the voltage varies (e.g. 100mV to 600mV) then it's time to replace the catalytic converter. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

 

[Mark]

I checked the O2 sensors when she went for fuel. They appeared to be working in the same manner as my 1998 DI.

As for the O2 Sensors, the replacement sensors ordered were with the black connector.

Leaded fuel: SHe has been an ardent user of 93 Premium, but that does not mean the previous owner had not used 87 Unleaded.

Engine coolant sensor??? How to check? (I'll Google that later)


I have cleared the codes twice and they kept coming back.

However, I do 'hear' the death rattle of a CAT, the metallic vibration, but both cats (to throw both codes.)

Thanks for the suggestions and they will be considered.

 

[basstard440]

try cleaning the mass airflow sensor and reset the codes. My disco will throw all o2 codes when it gets dirty. Let us know how you make out. Joe

 

[DirtyDisco]

Haha 0420... maybe your Rover wants to smoke some ***