Advice re: Code P0421 & Warm-up Cat

T

tlahood

:
2002 Protege5
I see that this topic has been addressed previously, but not very recently, so maybe there's a new solution by now. My 2002 P5, 189K miles, shows P0421 code indicating a poorly performing pre-cat. I tried CataClean and the isolating the rear 02 sensor, both of which did nothing to improve things (and now I'm out an 02 sensor!).

Is it worth buying new, CA-compliant cat at this point? The dealer wants $1200 (likely more than the car is worth) and an independent shop wants $800 to replace it, although they will install one bought elsewhere for $75. And what happens if the cat is replaced and the code still appears?

Please forgive what must seem like 'duh' questions, but I'm new here and don't really know the protocol.

Thanks!
 
Do the non-fouler mod, and make sure your primary cat is working well. You should have no trouble passing emissions with that setup.

I believe the only way you can get porked on this is if they do a visual inspection and see the spacer on the 02.
 
MrGiggles said:
Do the non-fouler mod, and make sure your primary cat is working well. You should have no trouble passing emissions with that setup.

I believe the only way you can get porked on this is if they do a visual inspection and see the spacer on the 02.
Click to expand...

How can you make sure your main cat is functioning properly before you do the non-fouler mod?
 
stormkyori said:
How can you make sure your main cat is functioning properly before you do the non-fouler mod?
Click to expand...

With an emissions test, or by getting the inlet and outlet temps of the cat. The outlet should be considerably hotter than the inlet.

There are articles out there that go through the process.
 
Last edited:
"the outlet should be considerably hotter than the inlet." :)

Sent from my Nexus 6 using Tapatalk
 
MrGiggles said:
With an emissions test, or by getting the inlet and outlet temps of the cat. The outlet should be considerably hotter than the inlet.

There are articles out there that go through the process.
Click to expand...

I've seen the method done on youtube and user talking about it but I don't see anyone mention which sensor, if it's up or down
 
where can I buy a non fouler for the P5? I see so many how to's on youtube and many are available on amazon but I don't want to buy one that doesn't fit. Can someone direct me to save me the hassle of trial and error?
 
I've been having this code once it got cold out.. My fix was Injector cleaner and then pulling up next to a fancy new Civic. Check engine light went off at 6k rpm ;)
 
I haven't fixed my CEL with the same code as stated above. Can you get away with just your main cat? I was quoted $500 or so for a new CA-compliant cat from my mechanic. Would that amount be better spent elsewhere? I've been racking my brain because I have a few things I want to do to the car that would help if I had that amount to use.
 
stormkyori said:
I haven't fixed my CEL with the same code as stated above. Can you get away with just your main cat? I was quoted $500 or so for a new CA-compliant cat from my mechanic. Would that amount be better spent elsewhere? I've been racking my brain because I have a few things I want to do to the car that would help if I had that amount to use.
Click to expand...

Yes. Vet the CEL to go away with the non-folder, make sure your main cat is working well, and you're good to go.
 
Did the anti-fouler on mine this weekend. After a few trips for re-learn, the CEL shut off today. Ended up costing me about $20 for the anti-fouler and the O2 sensor socket. Took about 20 minutes.
 
MrGiggles said:
Yes. Vet the CEL to go away with the non-folder, make sure your main cat is working well, and you're good to go.
Click to expand...

IMAG1523.jpg


Just did this yesterday and it threw out these codes P0140 & P0037. Is this something I fix with a new sensor with the non-fouler method. Silver linning, no cat code.
 
Sounds like your O2 sensor is completely dead.
The sensor and the heater for it.

Check for open circuits... (make sure it's plugged in)




 
stormkyori said:
IMAG1523.jpg


Just did this yesterday and it threw out these codes P0140 & P0037. Is this something I fix with a new sensor with the non-fouler method. Silver linning, no cat code.
Click to expand...

I had a persistent P0037 and a new 02 sensor fixed it. Check that the plug is secure, and check for voltage on the two wires that supply the 02 sensor heater coil. You should also be able to check the 02 heater for resistance, but I don't know the specs for that.

Mine will set a PO140 once in a blue moon. Normally after a lot of rain. I just clear it and it's good for another couple months.
 
pcb said:
Sounds like your O2 sensor is completely dead.
The sensor and the heater for it.

Check for open circuits... (make sure it's plugged in)
Click to expand...

Not sure what you mean by that. Although I do somewhat understand what the diagrams say, does that mean I need to buy a new one? When I was doing the non-fouler, the sensor itself was almost black. I'm not as mechanically gifted as some of you. I'm just a guy that doesn't mind getting his hands dirty and learning more about my own car. I don't have a complete set if tools, getting there.
 
stormkyori said:
Not sure what you mean by that. Although I do somewhat understand what the diagrams say, does that mean I need to buy a new one? When I was doing the non-fouler, the sensor itself was almost black. I'm not as mechanically gifted as some of you. I'm just a guy that doesn't mind getting his hands dirty and learning more about my own car. I don't have a complete set if tools, getting there.
Click to expand...

The post-cat sensor has it's own heater that gets it up to temperature faster. P0037 sets when there is a fault in that circuit.

That's why that sensor has 4 wires instead of just one like the pre-cat 02.
 
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