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Mazda 323 P0421

  #1  
Old 03-08-2016, 08:10 AM
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Default Mazda 323 P0421

Hi All,

I picked up a '03 Reg 2.0L Mazda 323 last week. it had no issues at the time but around 100 miles later it popped up an error code (believe P0038). I cleared it and asked the old owner who said he had the same thing, cleared and it had not returned since. it did not come back for another 50 miles when I cleared again.

I drove around 100 miles after this and the engine warning light started flashing and I lost power fast. I pulled in, waited, and then was able to continue back. At this point I had 3 errors - P0443, P0300, and P0038. A mechanic had a look and pointed out a raised coil pack with a small crack. I got this changed to a new one and at the same time changed the spark plugs and cam belt.

Around 150 miles later the engine warning light came on. The car still drives smooth and this time the code is P0421. A google indicates it could be the cat or a sensor, could someone confirm how I might be able to check which one?

It's still driving very smoothly with no high idle or roughness at all. i hope it's the O2 sensor as obviously this is a much cheaper part and I've already put a fair bit into the car.

All help very appreciated!
 
  #2  
Old 03-11-2016, 08:19 AM
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Bump anyone? Just need to know whether this is going to cause any real issues and if so whether the likelyhood is bad sensor?
 
  #3  
Old 03-11-2016, 09:09 PM
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At the moment, I'm not at work & don't have 323 manuals online.
Looking at both 2.0, 2.3 & 2.5 Mazda 3s, DTC P0421:00 Warm up catalyst system efficiency below threshold

POSSIBLE CAUSE
Leakage exhaust system
A/F sensor looseness
HO2S looseness
WU-TWC deterioration or malfunction
PCM malfunction


It's pointing towards a bad convertor, most likely the previous issues have blocked or deteriorated the cat.
 
  #4  
Old 03-12-2016, 03:29 AM
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Hi grim_reaper thanks so much for getting back to me.

Is there any way to check what's wrong before I get the work done?

If it is the cat what kind of cost am I looking at?
Originally Posted by grim_reaper View Post
At the moment, I'm not at work & don't have 323 manuals online.
Looking at both 2.0, 2.3 & 2.5 Mazda 3s, DTC P0421:00 Warm up catalyst system efficiency below threshold

POSSIBLE CAUSE
Leakage exhaust system
A/F sensor looseness
HO2S looseness
WU-TWC deterioration or malfunction
PCM malfunction


It's pointing towards a bad convertor, most likely the previous issues have blocked or deteriorated the cat.
 
  #5  
Old 03-12-2016, 11:47 PM
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I agree with grim. Cats are just coated with the material necessary to treat harmful exhaust gasses. A misfire, (P0300, P0301-04), allows raw fuel to run thru the cat destroying the material. The older the cat, the less likely it is to withstand a barrage of raw fuel. If you have access to a scanner that will run live data, you can watch the reaction of the pre cat and post cat O2's, you will be able to determine the condition of the cat.
 
  #6  
Old 03-14-2016, 07:44 AM
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Thanks Sparky, that does make sense though obviously want to confirm first just to be safe.

I've just ordered a reader so I'll post figures on here when it arrives.
 
  #7  
Old 03-14-2016, 09:30 PM
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When watching the signals from the reader, depending on how it works, the pre cat O2 sensor will show high and low readings that should change at a steady rate like a wave. The post O2 should be at a steady reading. If the O2's mirror each other, that indicates the post O2 is seeing the same exhaust as the pre O2 and the cat is doing nothing. Dead cat.
 
  #8  
Old 03-15-2016, 07:22 AM
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Poor *****.
 
  #9  
Old 03-18-2016, 02:21 PM
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Right so my OBD2 arrived today. It was a little bluetooth one so used the Torque app to check the sensors. There was several options - 02 volts bank 1 sensor 1,2,3,4 and o2 volts bank 2 sensor 1,2,3,4. I added all but only got a reading from bank 1 sensor 1 which showed the flowing diagram as mentioned before (between 0.7 and just above 0). If I'm getting no reading from bank 2 does that mean the sensors gone or that the car doesn't support this OBD2? Really hope it's the sensor!
 
  #10  
Old 03-18-2016, 09:10 PM
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You only have bank one in this engine. In-line 4 engines have only one bank: bank 1. V6 and V8 engines have two banks.
 

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