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GMC Forum: exhaust question on a 2000 jimmy
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Old 12-02-2010, 08:19 PM
roldaphat9 roldaphat9 is offline
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Default exhaust question on a 2000 jimmy

I have a 2000 jimmy and it has had some exhaust work done before I bought it. New muffler 50k miles ago and a new cat about 40k miles ago. but my SES light came on and gave me a p0420 code which referes to the low efficiency threshold of the cat in bank1. A mechanic said there could be 2 cats on this vehicle.. So my question is How many cats come on a 2000 stock Jimmy? I remember lookin under the truck and only seeing one, and it had the exhaust header that came to only 1 pipe to the cat then to the muffler, is this normal? Or is it supposed to have dual pipes underneath there? the mechanic said that the bank 1 refers tot he driver side cat?
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Old 12-02-2010, 09:49 PM
Molson02536 Molson02536 is offline
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Originally Posted by roldaphat9 View Post
I have a 2000 jimmy and it has had some exhaust work done before I bought it. New muffler 50k miles ago and a new cat about 40k miles ago. but my SES light came on and gave me a p0420 code which referes to the low efficiency threshold of the cat in bank1. A mechanic said there could be 2 cats on this vehicle.. So my question is How many cats come on a 2000 stock Jimmy? I remember lookin under the truck and only seeing one, and it had the exhaust header that came to only 1 pipe to the cat then to the muffler, is this normal? Or is it supposed to have dual pipes underneath there? the mechanic said that the bank 1 refers tot he driver side cat?
Swap the pre Cat O2 sensors and clear the code. If it comes back you may have either bad O2 sensors or bad cat. You have 2 per Cat O2 sensor, Bank 1 (P0420) and bank 2 (P0230).

Short explanation, the ECM is looking to make sure that number of crossings by the post-cat sensors is significantly less than the pre-cat ones. This implies that the converter is able to store the oxygen. A degraded sensor never switches fast, rather it becomes lazy. If front becomes lazy, then in theory computer could miss-interpret because then both pre-cat and post-cat would be switching similarly albeit lot slower.

HOWEVER, when the front becomes lazy, the driveability will be affected severely and you will get code for the pre-cat sensor. If you have no other driveability symptoms and if the only code you get is P0420/P0430, then in almost all cases your converter has been degraded enough for the computer to throw the code BUT not enough to really affect your emissions. All the literature over web will give many papers where the actual tail pipe emission and the federal emission tests run on a car with P0420/P0430 came out clean.

Other issues also that will cause both P0420/P0430 to show up would be a dirty MAF sensor and will need to be cleaned, but only one P0XXX code shows up could be a bad O2 sensor or a bad fuel injector running your #1 bank lean.

Oh and yes the Jimmy only has one Catalytic converter, you have the down pipe from the drivers and passenger side where the O2 sensors are located and then go to a Y pipe to the catalytic converter. After the Converter is the third O2 sensor which monitors the performance of the Catalytic converter.

Good luck and keep us posted.
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Old 12-03-2010, 08:28 PM
roldaphat9 roldaphat9 is offline
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ohh ok that makes sense... it has been running kinda weird off and on, especially when its a cold start, it tends to kinda sputter a little, not really bad but its enough to feel it. so from what your saying, it could be the front 02 sensor, throwing the code and causing it to drive crappy like that, correct? where are the first 2 o2 sensors located?
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Old 12-03-2010, 08:39 PM
Molson02536 Molson02536 is offline
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Originally Posted by roldaphat9 View Post
ohh ok that makes sense... it has been running kinda weird off and on, especially when its a cold start, it tends to kinda sputter a little, not really bad but its enough to feel it. so from what your saying, it could be the front 02 sensor, throwing the code and causing it to drive crappy like that, correct? where are the first 2 o2 sensors located?
Here is a link to your exhaust system on your Jimmy. #10 are the two O2 sensors that are in question and the one on the driver's side is the one that needs to be address from the code you have giver P0420.

http://www.compnine.com/index.php?u=...03&grouptype=B

Good luck and keep us posted, at worst, it's going to be a bad fuel injector on your driver's side of your engine that may have an issue since P0420 also indicates that side of the engine is running lean. Personally I would inspect the rear O2 sensor #16. More common for the rear O2 sensor to go bad if the pre cat and post cat O2 sensor readings are the same that would cause you to have the DTC code P0420.

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

Some suggested steps for troubleshooting a P0420 error code include:

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

Last edited by Molson02536; 12-03-2010 at 08:48 PM.
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