Oxygen Sensors Code P0420 Issues

[ICE_BM]

Hi folks,

I have the dreaded P0420 problem, it's mentioned in various places but does not have a specific thread, I think it needs it's own thread because the repair costs are very high and so I want to get opinions from others about options and see what others have tried...

So the code P0420 means "Catalytic Converter Efficiency Below Threshold".

There are four oxygen sensors on the car, pre-cat and post-cat, one set per bank. The code means that for one side (or both) the sensors do not compare properly and so the ECU thinks that the CAT(s) are not working properly so the code is set, this code is 'latched' and needs a scan-tool to clear it. The (slighly crazy) side effects of codes are:
Flashing CRUISE light (cruise cannot be used)
Traction Control OFF light (dunno if it's off or on)
Flashing [S] light (locked in sport mode)
CEL (check engine light) ON

Cost of the sensors is about $350++ PER EACH sensor, so random replacement seems a little harsh, my car has done less than 70k and this problem has been around since I got the car at 55k (probably why the previous owner sold it...)

Anyway, can any members tell me if they have tried DENSO or BOSCH aftermarket (direct fit) sensors and if there are any issues with these?

cheers

[Tradewind]

Headache material

Have your vehicle retuned, they can adjust the parameters for this code, it will go away for good and you vehicle will run perfectly too

[ICE_BM]

Runs ok now, just uses more fuel than it 'should', so perhaps there could be an issue.

I have a scan tool so I just keep resetting the code, but now it comes back more often so maybe a sensor is actually dying now.

Anyone know what PID numbers the rear sensors can be checked on (using a computer-based scan tool)? I can find the front sensors in the data list but not the rear ones.

[KiDo_Tuning]

Runs ok now, just uses more fuel than it 'should', so perhaps there could be an issue.

I have a scan tool so I just keep resetting the code, but now it comes back more often so maybe a sensor is actually dying now.

Anyone know what PID numbers the rear sensors can be checked on (using a computer-based scan tool)? I can find the front sensors in the data list but not the rear ones.

P0420 is rear O2 sensor It determines that the gas flow is too hot and throws a code, thinking the catalytic converter is missing or failing

Easier to turn off in a tune. Is it manual or auto?

[3rspecb]

From memory the rear 02 sensors are used to control fueling in closed loop, so by disabling them your fuel consumption may increase..

Garage 88 (phat GT) can get these in at a cheaper price then subaru dealership..

[ICE_BM]

I have now read the blurb on KIDO and I am keen for a tune because there are so many things that I feel are 'wrong' about the way the car behaves.

I have not had the car since new so maybe somebody has already messed with it, I guess by logging some data as part of the tuning process then I/we will learn if everything is behaving as it should.

I will PM Matt to find out how to get the tuning process started, and will keep the forum posted how it goes (my H6 is auto with SI drive)

[KiDo_Tuning]

From memory the rear 02 sensors are used to control fueling in closed loop, so by disabling them your fuel consumption may increase..

Garage 88 (phat GT) can get these in at a cheaper price then subaru dealership..

Disabling the code does not increase fueling since the O2 sensor failing zeros out the AF#3 learning values, with the rear O2 typically adding fuel on a H6 in stock form. Rear o2 sensor can be turned off as well(as per romraider thread)