1997 P0420 code

1997 P0420 code

Postby doc_k [OP] » January 21st 2015, 8:19pm

Hi everyone.

I just got a CEL on and read the code P0420 code. What is the most likely cause of this on a 1997 Astro?
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Re: 1997 P0420 code

Postby chevymaher » January 21st 2015, 10:21pm

Dunno what is the description for that code?
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Re: 1997 P0420 code

Postby The Drummer » January 21st 2015, 10:49pm

''USE THE TORQUE LUKE ''




and beware of trees ,them nasty wooden things are evil .
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Re: 1997 P0420 code

Postby doc_k [OP] » January 21st 2015, 11:31pm

P0420 = catalytic converter low effieceny
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Re: 1997 P0420 code

Postby chevymaher » January 21st 2015, 11:41pm

Cat getting some age and less efficient.
Could be a weak O2 sensor.
Spitting injectors. make it run rich and fouls them.
Tune up and run her hard every once in a while. Keep her cleaned out.
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Re: 1997 P0420 code

Postby kennysmoke » January 21st 2015, 11:59pm

PO420 = previous owner was pot head....
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Re: 1997 P0420 code

Postby Sailing_Faith » January 22nd 2015, 1:46am

kennysmoke wrote:PO420 = previous owner was pot head....



You should get a p187 code for that one....


... Cause yOu are killin me! :rofl:
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Re: 1997 P0420 code

Postby doc_k [OP] » January 22nd 2015, 2:04am

How do I determine it's a bad cat?
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Re: 1997 P0420 code

Postby thegreenmachine » January 22nd 2015, 2:15am

doc_k wrote:How do I determine it's a bad cat?


If it climbs on the counter and licks the milk from your cereal bowl.
"that looks legit"

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Re: 1997 P0420 code

Postby sadglad » January 22nd 2015, 3:18am

It could be as simple and cheap as a vacuum leak. See here. viewtopic.php?f=24&t=50657
New cat is expensive. Check the cheap and easy stuff first.
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Re: 1997 P0420 code

Postby chevymaher » January 22nd 2015, 3:40am

doc_k wrote:How do I determine it's a bad cat?

Check everything. O2's make sure it is tuned correctly. Good cap rotor wires. Vacuum leaks was a good tip. Once it is running right run it on the freeway a half hour. If it isn't the cat or it is just getting weak. It will clear the code and it wont come back for a long time.
Once you are sure it has good ignition. Injectors are clean and working correctly. If it then stays off as long as you are running on the freeway but keeps popping up in traffic. Then we leaning toward the cat being shot.

Mom's cat is dead as a doornail. But before she tested it I would put injector cleaner in it. And just wail the tar out of it a hour or so. She would go test and it passed. Then after a couple weeks it came back. The code I mean.
We went through that for years before she moved back home. Now it don't matter they don't test here.
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Re: 1997 P0420 code

Postby redfury » January 22nd 2015, 2:21pm

If you have a IR temp gun, you can look at the cat temps to see if it's heating up properly. A rear O2 sensor that isn't reporting correctly will also trip the code...you can see that on a scan tool that can read live data. Unlike the front O2 sensors, it should hover around .450mv instead of fluctuating above and below like the upstream sensors do.
A temporary fix usually becomes a permanent solution, therefore it does not exist.
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Re: 1997 P0420 code

Postby doc_k [OP] » January 22nd 2015, 8:20pm

The only tests I made so far are with an actron CP9145 code scanner which gave me the P0240. I can look at data and all o2 sensors fluctuate. The actron doesn't graph, but the O2/2 sensor which I believe is the downstream one fluctuates from .045 to .855 v. It's hard to read because it's constantly jumping. The van also used to make this rattleling noise. My brother said it was from the cat (heard it while under van, he said honeycomb was cracked). It's not rattleling anymore. Where do I measure temp on the cat? Van needs emissions testing soon!!
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Re: 1997 P0420 code

Postby redfury » January 22nd 2015, 9:11pm

Rattling cat means your honeycomb has broken down unless it was a loose heat shield. You're looking at a new cat. The rear O2 should be steady, not acting the same as the upstream sensors. The fact that it is means nothing is happening in the cat to convert the gasses. I don't see any other solutions.
A temporary fix usually becomes a permanent solution, therefore it does not exist.
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Re: 1997 P0420 code

Postby doc_k [OP] » January 28th 2015, 2:26am

Can an air/vacuum leak cause the downstream o2 sensor to fluctuate, or is it a certainty that the cat is bad? Is there another way to determine/coorberate a bad cat?
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Re: 1997 P0420 code

Postby Meterpig » January 28th 2015, 2:31am

thegreenmachine wrote:
doc_k wrote:How do I determine it's a bad cat?


If it climbs on the counter and licks the milk from your cereal bowl.



:clap:
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Re: 1997 P0420 code

Postby WoodButcher » January 28th 2015, 3:09am

redfury wrote:Rattling cat means your honeycomb has broken down unless it was a loose heat shield. You're looking at a new cat. The rear O2 should be steady, not acting the same as the upstream sensors. The fact that it is means nothing is happening in the cat to convert the gasses. I don't see any other solutions.



ditto that^^^
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Re: 1997 P0420 code

Postby doc_k [OP] » January 28th 2015, 11:09pm

Where are the o2 sensors, especially the last downstream one? I see two on either side of x over pipe after flange but none on cat or after.
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Re: 1997 P0420 code

Postby WoodButcher » January 29th 2015, 1:55am

I haven't been under my '97 in a while but IIRC it was on the cat itself. Look on Rock auto for the part and you should find a picture.

Expensive GD pipe it is.
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Re: 1997 P0420 code

Postby doc_k [OP] » January 29th 2015, 2:14am

There is nothing on pipe or cat. There is no wire harness or connector. How can this be read 0420 without a post(downstream) sensor? HELP!
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