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The ECL on my 9-3 has been on for a while now and I finally decided to get the code read in an attempt to get rid of thing. I took the car to a local garage and was told the code is P0420. I did a bit of research on this and the general concensus seemed to be to change the rear o2 sensor. After 2 days trying to remove the old sensor (to no avail:cry:) I decided it would probably be easier to take off the whole cat and do the job on the bench (big red wrench on stand by). After I got the cat off it was clear that the pre cat seems to be shot (lots of rattling and bits actually falling out the pipe). Rather than replace the sensor on a bad cat, I thought I best look into replacing the whole thing. However after looking into getting a new cat I'm confused as to which one I should be buying. My car is a 2001 (51 plate) 9-3 eco 2.0 lpt (B205E?). The one I took off obviously had a pre cat but all the cat suppliers websites point me to the no pre cat pipe. I am now wondering whether a previous owner had replaced the cat with an incorrect one. If anyone could help me with the following I would be very gateful.
1. Does the cat actually need to be replaced as it is only the pre cat the rattles?
2. Should my car have a pre cat?
3. My car has two o2 sensors. Would a car without a pre cat just have one?
Sorry for the long post :D.
 

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The ECL on my 9-3 has been on for a while now and I finally decided to get the code read in an attempt to get rid of thing. I took the car to a local garage and was told the code is P0420. I did a bit of research on this and the general concensus seemed to be to change the rear o2 sensor. After 2 days trying to remove the old sensor (to no avail:cry:) I decided it would probably be easier to take off the whole cat and do the job on the bench (big red wrench on stand by). After I got the cat off it was clear that the pre cat seems to be shot (lots of rattling and bits actually falling out the pipe). Rather than replace the sensor on a bad cat, I thought I best look into replacing the whole thing. However after looking into getting a new cat I'm confused as to which one I should be buying. My car is a 2001 (51 plate) 9-3 eco 2.0 lpt (B205E?). The one I took off obviously had a pre cat but all the cat suppliers websites point me to the no pre cat pipe. I am now wondering whether a previous owner had replaced the cat with an incorrect one. If anyone could help me with the following I would be very gateful.
1. Does the cat actually need to be replaced as it is only the pre cat the rattles?
2. Should my car have a pre cat?
3. My car has two o2 sensors. Would a car without a pre cat just have one?
Sorry for the long post :D.
I don't know about UK cars. I am surprised that the consensus for your code is that the second O2 sensor has failed, as a quick google search shows that P0420 is generally regarded as cat failure.

My secondary O2 went bad, and the code it usually threw was P1117 (heater element pre heat current too low), with P0141 (no activity detected on sensor) thrown in occasionally for variety. I did get the sensor out, using a slightly longer-than-usual box-end wrench: no room to get a socket on the sensor. After replacement, no codes.
 

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The ECL on my 9-3 has been on for a while now and I finally decided to get the code read in an attempt to get rid of thing. I took the car to a local garage and was told the code is P0420. I did a bit of research on this and the general concensus seemed to be to change the rear o2 sensor. After 2 days trying to remove the old sensor (to no avail:cry:) I decided it would probably be easier to take off the whole cat and do the job on the bench (big red wrench on stand by). After I got the cat off it was clear that the pre cat seems to be shot (lots of rattling and bits actually falling out the pipe). Rather than replace the sensor on a bad cat, I thought I best look into replacing the whole thing. However after looking into getting a new cat I'm confused as to which one I should be buying. My car is a 2001 (51 plate) 9-3 eco 2.0 lpt (B205E?). The one I took off obviously had a pre cat but all the cat suppliers websites point me to the no pre cat pipe. I am now wondering whether a previous owner had replaced the cat with an incorrect one. If anyone could help me with the following I would be very gateful.
1. Does the cat actually need to be replaced as it is only the pre cat the rattles?
2. Should my car have a pre cat?
3. My car has two o2 sensors. Would a car without a pre cat just have one?
Sorry for the long post :D.
I've seen similar error codes on other cars that were indeed failed O2 sensors, from your discription, you might well be facing a true pre-cat failure.

Probably the least expensive path would be to move the 2nd O2 sensor to after the 2nd cat and clean out the damaged remains of the pre-cat.

I'm unsure of the UK spec cars, can't say if your car should have had the dual cat or single cat setup. Either way, I'd expect either system to have the 2nd O2 sensor. I doubt a prior owner of the car had the ECU altered to monitor the 2nd O2 sensor to match a replacement down pipe. If the car orginonally only had the 1 O2 sensor, it'd have far easier and much less expensive to simply plug the 2nd sensor bung.
 
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