2004 Chevy Impala OBD

TUPAC2

MEMBER
2004 CHEVROLET IMPALA
6 CYL
4WD
AUTOMATIC
108,488 MILES

My 04 impala LS keeps showing 2 codes when a code reader is connected, 1 being P0420 and P0420(pending)i looked up the definition and it says catalyst eff. Below threshold (bank 1), this all started after a drive on the expressway home from work during a storm and the light has been on ever since so my question is does these codes mean that the converter is gone or is it sumthing I am missing as to what else may be causing these codes any things you suggest I check to remedy this would be greatly appreciated, was thinking of changing the 02 sensor but haven't been able to tell which one is the bank 1 snsor, also whenever the car accelerates there is a water swishing noise on the pass side floorboard that s constant for awhile then settles it seems after the car is driven for a prolonged amount

Tuesday, November 18th, 2008 AT 8:36 PM

5 Replies

JACOBANDNICKOLAS

MECHANIC
110,052 POSTS

Hi:

This code is generic and is the same on all vehicles.

P0420 = Catalyst System Efficiency Below ThresholdCatalyst System Efficiency Below Threshold.

This means that the secondary O2 sensor detects that the catalytic converter isn't working as efficiently as it should.

This engine code can be triggered by any one of the following:

1.) The catalyst in the catalytic converter is cracked, clogged, or otherwise damaged.
2.) The secondary O2 sensor is malfunctioning.
3.) There is an exhaust leak.

As far as bank 1, that just refers to the side of the engine with the number 1 cylender.

As far as the water noise you're hearing, it's most likely coolant entering the heater core. Make the coolant level (rad and overflow) are full.

Let me know if you have any other questions.

Joe

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Tuesday, November 18th, 2008 AT 10:58 PM

TUPAC2

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3 POSTS

Joe
Thanx for the assist Joel, but answer me this if you can what is the best way to find out which one of the 3 things you listed is the root of my problem I have to past emission soon and I'm wondering if there is something I can do before totally replacing the cat converter for example if the cat is just clogged what would be the best way to un-clog it cause as I stated in my previous msg this all started on that rainy night going thru the puddles on the expressway, I had no problems before then

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Wednesday, November 19th, 2008 AT 6:44 PM

JACOBANDNICKOLAS

MECHANIC
110,052 POSTS

Hi:
If this started on a rainy night, my guess would be it's cracked. As you most likely know, they run very hot and maybe the cold water hitting it damaged it. Inspect it for damage. Also, make sure the exhaust feels and sounds clear. There is a technique to check the back pressure by removing the O2 sensor and checking the pressure with a gauge. If you're interested, I'll have to look up the process for your vehicle.

Let me know.
Joe

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Wednesday, November 19th, 2008 AT 10:07 PM

TUPAC2

MEMBER
3 POSTS

Thanx Joe I would appreciate it alot if you would provide me with that technique hopefully with that methiod I would truly know if the converter needs to be replace rather than just going out and replacing it and didn't need to, any othe suggestion you could provide to try detect if I need to replace it would be good also, what or how could I find out if it's just clogged because the exhaust feels clear and there is no abnormal sounds coming from the exhaust

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Thursday, November 20th, 2008 AT 7:51 PM

JACOBANDNICKOLAS

MECHANIC
110,052 POSTS

Hi:

Ok, here we go:

Hi:

Ok, here we go.

1) Remove position 1 HO2 (heated oxygen sensor).

2) Install a exhaust back pressure gauge in the O2 sensor's place.

3) Start the car and let it run.

4) Rev the engine to 2500 RPM's.

5) Watch the gauge. It should not exceed 1.25 PSI.

6) If it doesn't, everything is ok. Replace the O2 sensor.

7) If it does exceed spec, replace the sensor and remove HO2 in position 2.

8) Perform the same process.

9) If the pressure doesn't exceed the spec, check the muffler and resonator for internal failure and the exhaust for amage.

10) If the pressure exceeds spec (1.25 psi) replace the converter.

NOTE: Remember everything you're working with is very hot. Also, I've uploaded pictires of both sensors. Keep in mind, when replacing the sensors, antiseeze should be used on the O2 sensors' threads.

Positopn 1