Dumb CAT question!!!!

This is a pretty dumb question but here goes it. If the cat is bad can it set off the check engine light?

Most definately. I'd have the codes read first before jumping in to replace the Cat. Could be a number of things that mimic a bad Cat.

Cool Thanks.

It depends on if newer or older year. You did not say what year or engine.
Also even it you have a cat code it doe not always nmean a cat is bad.
Any number of things can cause a cat code.
Like this link.
http://www.troublecodes.net/articles/catfailure/
And a little more info below.
DTC P0420, P0421, P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicates bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicates bank 2 catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code(s) is not present, go to next step. If misfire code(s) is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC . Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Ć Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engineand raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.

Its a 97 blazer 4.3

Yes a 97 can set a cat code. Almost all 96 up OBD11 can set cat codes. Some makes have cats on both sides. But cat codes 420/430 will point you in the right direction.
Are you having any problems or is it setting a code or check engine light?
Or was you just asking to find out what a cat would or could do?

ohh k....ill be removing my cat shortly...I like cats....they tast like chicken....

Don't remove it before checking your codes!!!

ohh k....ill be removing my cat shortly...I like cats....they tast like chicken....

Aw man you relly need to cut down on eating that razor blade soup.:nono:
I do think that is a answer that belongs in this post.
It should be posted back in the smart cat answer forum.
In your best interest you should not be counting your cat/chickens dinners before they hatch. :grinyes: :lol:

But cat codes 420/430 will point you in the right direction.Are you having any problems or is it setting a code or check engine light? Or was you just asking to find out what a cat would or could do?


Yea It keeps setting codes. When scanned it showed the sensor before the cat was bad. I changed out both and its still setting the light off. I am not sure what the codes were or are. I am gonna get it re scanned. I work the next 4 dasy so it will have to wait till my dasy off. The cat kinda raddles at idle so thats why I asked if it can set off the light.


What do you mean by the 420/430 codes this code crap makes no sence to me. :)

those are the numbers for the codes. What were the code numbers that came up that led you to replace the O2 sensors? Just because a code points to a particular sensor or component, it doesn't necessarily mean that component is bad. The rattle very well could be the catalyst vibrating inside, but it could also be a heat shield or something else. Get back with us on the codes.

Yea It keeps setting codes. When scanned it showed the sensor before the cat was bad. I changed out both and its still setting the light off. I am not sure what the codes were or are. I am gonna get it re scanned. I work the next 4 dasy so it will have to wait till my dasy off. The cat kinda raddles at idle so thats why I asked if it can set off the light.


What do you mean by the 420/430 codes this code crap makes no sence to me. :)

Open your eyes and ears and mind real wide wide and read.:grinyes: :lol:
http://www.troublecodes.net/articles/catfailure/

I thought this was a good place to put this......I thought the backpressure excuse was a myth...and here is the prof...
http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

I thought this was a good place to put this......I thought the backpressure excuse was a myth...and here is the prof...
http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

It might be true with a 4 cycle motor, but not true with a 2 cycle.

That's why they have those tuned expansion chambers on a 2 stroke motorcycle. Take it off and it has no power.

I thought this was a good place to put this......I thought the backpressure excuse was a myth...and here is the prof...
http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

Well you had better read this. :grinyes: :lol:
http://www.automotiveforums.com/vbulletin/showthread.php?p=3647950#post3647950

my piont exactly.....you dont want to completely eliminate back pressure.....but if you know anything about racing engines...there is no scavanging but there is very little back pressure....quoted from the site you refered me to.....that only really happens on open headers.....