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Catalytic Converter Location

39K views 7 replies 5 participants last post by  sheila  
#1 ·
Hi, I had the same problem as many others on here code p0420. So I changed all the 02 sensors just in case and cleared the codes but within a week the mil was back on so I took it to the dealer since I was within the 8 year 80000 mile warrenty to check the cats. They said the cat on bank one was bad and replaced it but the light came back on the same day. I took it back and they cleared the codes and said it should be fine(this was today) but my question is, which cat is bank 1 and how many cats are there on the car? Is it possible they changed the wrong cat? Any help would be appreciated.............Tim :ford:
 
#3 ·
Bank 1 is the "rear" bank, nearest the firewall. Bank 2 is the "front" bank nearest the radiator
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How many cats are on the car? If you follow the pipe up from the rear of the car the first cat you see was not changed so im not sure if they changed the right one.
 
#4 ·
Not sure about the 4th Generation, but I believe they're the same as my 3rd Gen. There are 3 cats on the car. One in each bank of the engine then both bank flow into on converter on the end of the Y-pipe. As for the light coming back on right after the repairs were made, I wouldn't worry too much about it. I've read bulletins from GM that many vehicles that have the converters changed may have the SES light come on withing 100km of the repair. This is due to some sort of gassing that goes on in the new converter. I forget exactly what it's from, but it's nothing serious, just reset the light and all should be good.
 
#5 ·
Not sure about the 4th Generation, but I believe they're the same as my 3rd Gen. There are 3 cats on the car. One in each bank of the engine then both bank flow into on converter on the end of the Y-pipe. As for the light coming back on right after the repairs were made, I wouldn't worry too much about it. I've read bulletins from GM that many vehicles that have the converters changed may have the SES light come on withing 100km of the repair. This is due to some sort of gassing that goes on in the new converter. I forget exactly what it's from, but it's nothing serious, just reset the light and all should be good.
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Thanks for everyones input. I guess its safe to assume the mechanics at the dealer should know which cat to change if they read the code saying basically bad cat bank 1 (p0420 catalyst below threshhold bank one). I just remember going through this with the 02 sensors and the first mechanic I talked to telling me that the sensor in the front was bank one.
 
#6 ·
Thanks for everyones input. I guess its safe to assume the mechanics at the dealer should know which cat to change if they read the code saying basically bad cat bank 1 (p0420 catalyst below threshhold bank one). I just remember going through this with the 02 sensors and the first mechanic I talked to telling me that the sensor in the front was bank one.
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Yeah right :rolleyes2:

Bank 1 and 2 are also reffered to as "right hand and left hand". If the engine were inline with the vehicle, meaning the accessory belt / crankshaft pulley side faced the front of the vehicle, and the output / flywheel side faced the rear, bank 1 would be on the right, bank 2 on the left, from the driver's seat point of view. At least with Ford, when the engine is horizontally opposed for FWD applications, the bank reference does not change. Bank 1 = Right Hand, Bank 2 = Left Hand. The right hand bank is against the firewall, left hand behind the radiator.

So when the mechanic told you P0420 referred to the front bank, he was wrong.... However, he may have meant the upstream O2 sensor.... which again, he would be wrong. There are 3 cats on exhaust and 4 O2 sensors. There is one cat for each bank, and a 3rd cat located after Bank 1 and 2 exhaust merge. The 3rd cat does not have a sensor. Upstream sensors are sometimes called the "front", while downstream sensors the "rear". The correct way to identify the sensors is to label it Bank 1 Sensor 1 (right hand upstream) or Bank 2 Sensor 2 (left hand downstream), etc.

P0420 refers to Bank 1 Sensor 2 (right hand downstream). The downstream (aka "rear") sensor's purpose is to monitor the efficiency of the cat. If a cat goes bad, you'll get P0420 for Bank 1, and P0430 for Bank 2. Simetimes it is the sensor that has gone bad. The sensor gets "lazy" with age. The PCM references the sensor switching frequency. If the sensor switches slow, it sets a code. Usually this means the cat is bad, but if the sensor is old, it may be the sensor at fault. A diagnostic scanner will report the sensor switching speed. Compare that data with a tail pipe sniff test (emission tester). If the emissions are withing spec, the cat is working, if the cat has failed, emissions will be high and out of spec. It is much less expensive to replace an O2 sensor than a cat, so start there.
 
#7 ·
Not sure about the 4th Generation, but I believe they're the same as my 3rd Gen. There are 3 cats on the car. One in each bank of the engine then both bank flow into on converter on the end of the Y-pipe. As for the light coming back on right after the repairs were made, I wouldn't worry too much about it. I've read bulletins from GM that many vehicles that have the converters changed may have the SES light come on withing 100km of the repair. This is due to some sort of gassing that goes on in the new converter. I forget exactly what it's from, but it's nothing serious, just reset the light and all should be good.
My engine light stays on. But, I've been able to pass emissions, until this year. I put in a new catalytic converter, the light came back on within 30 to 50 miles, like it always does, so, now the code is for a 2nd catalytic converter, I never knew there would be more than one. It was a bit shocking, actually. Lololol. So, I'm wondering if I replaced the wrong one, but, I wasn't faced w any options or any mention that I had more than 1. Anyway. My car takes the whole fix or repair daily thing to a whole nother level. Lolololo.