2000 suburban, "check engne light" came on, Autozone says bad Catalytic Converter

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[ARCHIVED THREAD] - 2000 suburban, "check engne light" came on, Autozone says bad Catalytic Converter

Posted: 12/18/2010 8:45:13 AM EDT

So is this not really a problem? should I cut the converter out and straight pipe it? thanks!

Posted: 12/18/2010 8:46:08 AM EDT

[#1]

Quoted:
So is this not really a problem? should I cut the converter out and straight pipe it? thanks!

Won't get rid of the light.

Posted: 12/18/2010 8:46:09 AM EDT

[#2]

Posted: 12/18/2010 8:46:19 AM EDT

[#3]

That's an old suburban.

Posted: 12/18/2010 8:47:59 AM EDT

[#4]

vato-zone diagnosis =

Here's a question for auto-zone...........if the cat is dead.....why?

Posted: 12/18/2010 8:51:26 AM EDT

[#5]

Quoted:

vato-zone diagnosis =

Here's a question for auto-zone...........if the cat is dead.....why?

At least they don't charge for pulling the code and looking it up what it means. Some placed will charge you $50 just do to that. then $90/hr to find out what the problem really is then another $90/hr to fix it.

Posted: 12/18/2010 8:52:00 AM EDT

[#6]

Depending on you state's laws, straight-piping could be illegal.

Try using a couple cans of Sea Foam. Worked good on the wifes 99 Escort.

Posted: 12/18/2010 8:55:45 AM EDT

[#7]

Quoted:

Quoted:
vato-zone diagnosis =

Here's a question for auto-zone...........if the cat is dead.....why?

At least they don't charge for pulling the code and looking it up what it means. Some placed will charge you $50 just do to that. then $90/hr to find out what the problem really is then another $90/hr to fix it.

Any clue as to what a real scanner costs?

Posted: 12/18/2010 8:58:45 AM EDT

[#8]

Quoted:

Quoted:

So is this not really a problem? should I cut the converter out and straight pipe it? thanks!

Won't get rid of the light.

Yeah. In Illinois, any car after '96 is subject to emissions testing, which means some state flunky reads your codes. Any codes or check engine means you fail.

Posted: 12/18/2010 8:59:11 AM EDT

[#9]

Quoted:
Depending on you state's laws, straight-piping could be illegal.

Try using a couple cans of Sea Foam. Worked good on the wifes 99 Escort.

In what universe will Sea Foam repair a catalytic convertor? That stuff just cleans.

Posted: 12/18/2010 9:02:56 AM EDT

[#10]

Quoted:
Depending on you state's laws, straight-piping could be illegal.
Try using a couple cans of Sea Foam. Worked good on the wifes 99 Escort.

Its illegal everywhere ( duh the EPA) but since our state (south carolina) doesn't have inspections no one is going to know. Also to the OP if you cut the CAT out your still going to have an SES light. Is your truck doing anything peculiar? Usaully if you CAT is plugged and it does happen the truck will sputter. Ride around for a bit at night and stop and look under your truck, if its bad enough one of your CATs will be red hot ( i say one because you have two on your vehicle). Then again it could be numerous things. Maybe a sensor? You could straight pipe it but you would have to get a kit ( its basically a set of resistors) to fool you O2 sensors. Explore alittle more and see what you find.

Posted: 12/18/2010 9:14:11 AM EDT

[#11]

My Autoxray 6000 scanner cost $270. I have heard of some cheap ones setting off the air bag when you try to reset the codes.

The scan cannot tell AutoZone why it failed. An expensive scanner won't tell you any more. Straight piping it is against Federal law. No need to check your state law. I believe the fine is about $10,000. If you live in or move to an inspection state you will get found out. The vehicle is old enough for the cat to die of old age. Eventually the cat sites get plugged from contaminants in the fuel and so on. Running leaded fuel will plug it in a hurry. Chances are you are in for a replacement. On post-1996 (OBD II) systems the bad cat signal comes from the second O2 sensor (after the converter). I have never done it, but I have heard that there is a dummy second sensor available (eBay and elsewhere) that will blindly report to the computer that all is well. It is the first O2 sensor that provides feedback to the fuel injection. The second one is just a tattle tale.

Posted: 12/18/2010 9:15:23 AM EDT

[#12]

Quoted:

vato-zone diagnosis =

Here's a question for auto-zone...........if the cat is dead.....why?

Sometimes they plug up. A plugged cat can cause no end of troubles. Can be caused by a fouled plug, bad plug wires, bad O2 sensor or compression problems.

Posted: 12/18/2010 9:17:39 AM EDT

[#13]

Quoted:

Quoted:
Depending on you state's laws, straight-piping could be illegal.
Try using a couple cans of Sea Foam. Worked good on the wifes 99 Escort.

Its illegal everywhere ( duh the EPA) but since our state (south carolina) doesn't have inspections no one is going to know. Also to the OP if you cut the CAT out your still going to have an SES light. Is your truck doing anything peculiar? Usaully if you CAT is plugged and it does happen the truck will sputter. Ride around for a bit at night and stop and look under your truck, if its bad enough one of your CATs will be red hot ( i say one because you have two on your vehicle). Then again it could be numerous things. Maybe a sensor? You could straight pipe it but you would have to get a kit ( its basically a set of resistors) to fool you O2 sensors. Explore alittle more and see what you find.

We don't have any sputtering or anything peculiar that we can detect. Maybe a little trans slippage but that's not related. (wife normally drives it)

Posted: 12/18/2010 9:18:33 AM EDT

[#14]

Verify your knock sensors do not need replacing. If the cats are bad, there's something upstream that's causing that.

Knock sensors generally fail on the LS platform due to their poor protection in the intake valley, they get wet and corrode. They're about $45/ea, I recommend replacing them in pairs; You'll need a 10mm wrench to remove the intake, and a 3/4 socket or 7/8 socket to remove the sensors; it's advisable to build a valley of RTV around them to keep water out; I did this and haven't had any problems sense.

Posted: 12/18/2010 9:20:57 AM EDT

[#15]

you need to find an honest, knowledgeable mechanic... the “check engine” light may sometimes be ignored as nothing serious…need to have competent person check it out…

Posted: 12/18/2010 9:25:20 AM EDT

[#16]

It is against the law. Thousands of mustangs and camaros have straight pipes going all the way back.

Posted: 12/18/2010 9:28:22 AM EDT

[#17]

Quoted:
My Autoxray 6000 scanner cost $270. I have heard of some cheap ones setting off the air bag when you try to reset the codes.

The scan cannot tell AutoZone why it failed. An expensive scanner won't tell you any more. Straight piping it is against Federal law. No need to check your state law. I believe the fine is about $10,000. If you live in or move to an inspection state you will get found out. The vehicle is old enough for the cat to die of old age. Eventually the cat sites get plugged from contaminants in the fuel and so on. Running leaded fuel will plug it in a hurry. Chances are you are in for a replacement. On post-1996 (OBD II) systems the bad cat signal comes from the second O2 sensor (after the converter). I have never done it, but I have heard that there is a dummy second sensor available (eBay and elsewhere) that will blindly report to the computer that all is well. It is the first O2 sensor that provides feedback to the fuel injection. The second one is just a tattle tale.

A good scanner will run upwards of 5-7k and it will give info on why the cat failed...just requires someone other than a parts store flunky to interpret the info given.
things like LTFT and STFT will give some pretty good clues to finding the real problem.

Posted: 12/18/2010 9:28:36 AM EDT

[#18]

If your check eng. light is on because it failed a catalyst moniter, then cutting it out sure as hell won't turn the light off.

The little man in the dash wants to see his test pass; if your cat is dead then you need to replace it, or the O2 sensor(s) that he uses to run the test.

(or put a little piece of black tape over the light).

Posted: 12/18/2010 9:32:26 AM EDT

[#19]

Quoted:
That's an old suburban.

Hey! mine is an 01

Find a honest mechanic, My check engine light came on , I took it to my mechanic, He scanned it , said that's odd, let me clear it and see what happens. The was over a year ago and it hasn't came back on.

Posted: 12/18/2010 9:39:04 AM EDT

[#20]

Putting on a straight pipe might not clear the CEL. If your truck reads an O2 in front of and an 02 after the cat then the rear sensor will trip a code on a straight pipe since the temp will be off. You can buy a cheap rear 02 fouler to trick the computer if needed. My 02 Dakota did the same thing, the cat was clogged due to an egr problem. Replaced cat and a year later it was clogged again. You have to find the root cause of the cat problem or you will just be chasing parts.

Posted: 12/18/2010 9:40:26 AM EDT

[#21]

Might want to keep in mind that a vehicle with both upstream and downstream O2's (2000 Suburban, for example) will compare the readings from both to assess catalytic converter efficiency. If either O2 is faulty, it can throw the cat efficiency reading off. I have seen the "Catalytic Converter Efficiency Low" code set without setting the "Faulty Oxygen Sensor" code, even thought the problem was the O2.

I'm pretty sure the OP's vehicle has a bank 1 sensor, a separate bank 2 sensor, and a downstream sensor that's aft of the cat. The downstreams on most vehicles don't get hot enough off of the exhaust alone, and have a built in heater circuit. From the OP's post, I would have to say it's possible the downstream O2 is on the fritz.

While it's 100% possible that hte problem is in fact the cat, the last thing I'd do is replace the cat on a AZ diagnosis. I'd either pop for a more in depth diag, or replace the dwonstream O2 if I was in a gambling mood.

YMMV

Posted: 12/18/2010 9:41:50 AM EDT

[#22]

Quoted:
Depending on you state's laws, straight-piping could be illegal.

Try using a couple cans of Sea Foam. Worked good on the wifes 99 Escort.

Careful with this-that's what cooked the gaskets in my wife's car.

Posted: 12/18/2010 9:42:41 AM EDT

[#23]

What code was thrown?

Last time I was at "the zone" and got a code pulled, they gave me a little printout.

If the kid just said "you need a new cat" without further explanation and walked away, you need to do some actual investigating here.

Posted: 12/18/2010 9:44:02 AM EDT

[#24]

Could be anything making your light come on , air filter , oil change time, pcv valve but to get the light to go off .....just turn the key to the on position and pump the brakes 8 times !

Posted: 12/18/2010 9:45:24 AM EDT

[#25]

Quoted:

Quoted:
That's an old suburban.

Hey! mine is an 01

Find a honest mechanic, My check engine light came on , I took it to my mechanic, He scanned it , said that's odd, let me clear it and see what happens. The was over a year ago and it hasn't came back on.

The original title said 200 Suburban.

Posted: 12/18/2010 9:46:39 AM EDT

[#26]

GM cats have a propensity to go bad at around 100-150K and 10-12 years. Usually they rattle for a while and it's a pretty good clue they are breaking up inside.

If you try to cut it out, your secondary O2 sensor will code. Replacements are not that dang expensive IF you do it yourself.

Posted: 12/18/2010 9:47:00 AM EDT

[#27]

A little O2 sensor 101 here...the O2 sensor sees nothing but oxygen..it does not see fuel, or anything else...it is a single minded signal generator. knowing how it works makes interpreting scanner data easier.

Posted: 12/18/2010 9:49:07 AM EDT

[#28]

Quoted:
Could be anything making your light come on , air filter , oil change time, pcv valve but to get the light to go off .....just turn the key to the on position and pump the brakes 8 times !

I am having trouble with my girlfriend...do you have any advice?

Posted: 12/18/2010 10:03:37 AM EDT

[#29]

Quoted:

Quoted:
Could be anything making your light come on , air filter , oil change time, pcv valve but to get the light to go off .....just turn the key to the on position and pump the brakes 8 times !

I am having trouble with my girlfriend...do you have any advice?

Turn her to the On position and pump her eight times?

Posted: 12/18/2010 10:06:27 AM EDT

[#30]

Quoted:

Quoted:

vato-zone diagnosis =

Here's a question for auto-zone...........if the cat is dead.....why?

At least they don't charge for pulling the code and looking it up what it means. Some placed will charge you $50 just do to that. then $90/hr to find out what the problem really is then another $90/hr to fix it.

Any clue as to what a real scanner costs?

OOOH! OOOH! Pick me Pick Me! I know!

$10,000+

My buddy has a cheap one.

Posted: 12/18/2010 1:22:39 PM EDT

[#31]

Quoted:
Could be anything making your light come on , air filter , oil change time, pcv valve but to get the light to go off .....just turn the key to the on position and pump the brakes 8 times !

this did not work. tried twice.

Posted: 12/18/2010 1:25:45 PM EDT

[#32]

typo, sorry it is 2000

Quoted:

Quoted:
That's an old suburban.

Hey! mine is an 01

Find a honest mechanic, My check engine light came on , I took it to my mechanic, He scanned it , said that's odd, let me clear it and see what happens. The was over a year ago and it hasn't came back on.

The original title said 200 Suburban.

Posted: 12/18/2010 1:40:25 PM EDT

[#33]

Cut out the cats and buy two O2 simulators from these guys. http://www.afterthoughtsauto.com/o2sim.html

O2 simulators send a mild electrical signal to the computer telling it that the catalytic converter is doing its job. These factory sensors can be found after each cat before the exhaust pipe reaches the muffler.

1999 Chevy Tahoe LT 4x4 5.7L 350 ci V8.

Posted: 12/18/2010 1:45:57 PM EDT

[#34]

Stop going to Vato Zone for repair advice. The only thing they're actually qualified to do (and even this is debatable), is sell you parts.

Posted: 12/18/2010 1:47:01 PM EDT

[#35]

Quoted:
Might want to keep in mind that a vehicle with both upstream and downstream O2's (2000 Suburban, for example) will compare the readings from both to assess catalytic converter efficiency. If either O2 is faulty, it can throw the cat efficiency reading off. I have seen the "Catalytic Converter Efficiency Low" code set without setting the "Faulty Oxygen Sensor" code, even thought the problem was the O2.

I'm pretty sure the OP's vehicle has a bank 1 sensor, a separate bank 2 sensor, and a downstream sensor that's aft of the cat. The downstreams on most vehicles don't get hot enough off of the exhaust alone, and have a built in heater circuit. From the OP's post, I would have to say it's possible the downstream O2 is on the fritz.

While it's 100% possible that hte problem is in fact the cat, the last thing I'd do is replace the cat on a AZ diagnosis. I'd either pop for a more in depth diag, or replace the dwonstream O2 if I was in a gambling mood.

YMMV

Very good advice!!!! The O2 sensors, downstream of the cat, can and do fail. Guess what the "squawk" is? Catalytic efficiency below threshold !!!! Could simply be one or more bad O2 sensors, as they are used to measure cat performance.

This is especially true if you reset the code and it comes back right away.

Posted: 12/18/2010 1:47:31 PM EDT

[#36]

Got a check engine light on my 97 Tacoma once, read the code and it was that it no longer met CALIFORNIA standards, but was fine for upstate New York. But the shop said the only way to get rid of the light was to replace the CC. I just drove with the CE light on

Posted: 12/18/2010 1:57:48 PM EDT

[#37]

Quoted:
Verify your knock sensors do not need replacing. If the cats are bad, there's something upstream that's causing that.

Knock sensors generally fail on the LS platform due to their poor protection in the intake valley, they get wet and corrode. They're about $45/ea, I recommend replacing them in pairs; You'll need a 10mm wrench to remove the intake, and a 3/4 socket or 7/8 socket to remove the sensors; it's advisable to build a valley of RTV around them to keep water out; I did this and haven't had any problems sense.

Disconnect the knock sensor cable (two conductor, driver's rear top of the engine under the cover) and check it with a multimeter for voltage before pulling off the intake but usually the computer will tell you one has failed. Its a $500 job to have the shop do it if the one you put in to replace a bad one turns out to have been a factory defect (or you overtorqued it during installation, very easy to break so use an inch-pounds wrench) and you're tired of fighting with it.

He'll also need the fuel disconnect tool set, feed and return are different sizes. The harness disconnects from the knock sensors by squeezing the small sides (they're oval-shaped) and pulling.

Obviously I just went through it myself with my Yukon and found the repair manual a little confusing.

Kharn

Posted: 12/18/2010 2:17:05 PM EDT

[#38]

Only time my light on my Jeep has come on is when I had forgot to put my gas cap on after filling up. Took it to autozone and the code came back as some type of emission error. Bought a cheap cap screwed it on, autozone Guy reset the system and the light has never returned.

Posted: 12/18/2010 2:20:12 PM EDT

[#39]

fordguy owns a suburban?

Posted: 12/18/2010 2:22:47 PM EDT

[#40]

does your exhaust smell like rotten eggs? look on the bright side you can get a pretty penny for your old cat at your local scrap yard.

Posted: 12/18/2010 5:23:57 PM EDT

[#41]

Quoted:
A little O2 sensor 101 here...the O2 sensor sees nothing but oxygen..it does not see fuel, or anything else...it is a single minded signal generator. knowing how it works makes interpreting scanner data easier.

Interesting ...

Answer me this then . If an O2 sensor only sees oxygen than why is it's output low voltage when it detects a lean condition ( High O2 ) and a higher voltage
when it detects a rich condition ( Low 02 ) ?

Actually I'm just fucking with ya , but the truth is that O2 sensors do not detect oxygen . That's why they read low when the exhaust gasses are
lean with lots of O2 . They react to Hydrogen only . Which is present in small amounts when the exhaust gasses have little or no O2 content .
The sensors were originally designed to monitor the Hydrogen content of fuel cells for NASA . The name Oxygen Sensor is actually a mistake
made in an SAE paper that dealt with onboard analysis of exhaust gas content for internal combustion engines .