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Discussion Starter #1
Hello, I'm new to the forum, but not new to cars.

My Impala has some hesitation occasionally. Doesnt happen all the time, and only happens from a stop. Usually once the hesitation starts, I let off the gas and go again and its fine. The codes that are coming up:

P0404, P0405. The MPG is also suffering a bit (2-3 mpg lower than normal).

The mechanic I'm friends with said it might be the EGR valve acting up, but he wasnt 100% sure and told me to research. So I did..and found that other people with a similar issue replaced the EGR valve, to find that the problem still exists. Then they replaced the Cat and it was all fixed. Now before I go buying things that may or may not work, I thought I'd try my luck here with guys who know Impala's.

Any thoughts?
 

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A sure way to tell if the Cat is acting up is to have a scanner connected to the car that can watch the live data from the PCM and see what the O2 sensors are reading, especially the down stream sensors. I do not have the specs but if you find the specs and compare to the current reading that should help in deciphering whether the cat is the problem or the EGR.
 

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416 Posts
Hello, I'm new to the forum, but not new to cars.

My Impala has some hesitation occasionally. Doesnt happen all the time, and only happens from a stop. Usually once the hesitation starts, I let off the gas and go again and its fine. The codes that are coming up:

P0404, P0405. The MPG is also suffering a bit (2-3 mpg lower than normal).

The mechanic I'm friends with said it might be the EGR valve acting up, but he wasnt 100% sure and told me to research. So I did..and found that other people with a similar issue replaced the EGR valve, to find that the problem still exists. Then they replaced the Cat and it was all fixed. Now before I go buying things that may or may not work, I thought I'd try my luck here with guys who know Impala's.

Any thoughts?
Both of those codes lead towards the EGR valve
 

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6 Posts
Discussion Starter #5
A sure way to tell if the Cat is acting up is to have a scanner connected to the car that can watch the live data from the PCM and see what the O2 sensors are reading, especially the down stream sensors. I do not have the specs but if you find the specs and compare to the current reading that should help in deciphering whether the cat is the problem or the EGR.

Where can I get ahold of a scanner like that? Any mechanics shop would have?

I found a couple EGR valves for fairly cheap, I may just pick one up and see if it fixes the issue.
 
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