Wednesday, June 12, 2013

Check the EGR Valve on an a 1998, 1999, 2000, 2001 Nissan Altima

Description:
This post describes one of the diagnosis steps for the P0446 code on a 1999 Nissan Altima. Specifically the testing and replacement of the EGR Valve. This applies to all second generation Nissan Altimas which are 1998, 1999, 2000, 2001.

The EGR valve is a vacuum controlled valve which regulates the flow of exhaust gas into the intake manifold. The ability for the diaphragm portion of the valve to maintain a vacuum is essential for operation. This is what we are going to easily test in 5 minutes.

For more information on what this valve is or the function of the evaporative emissions system see my post about the P0446 Evaporative System Canister Vent Control Valve Circuit.

Location:
The EGR valve is located at the top center of the engine bay towards the rear firewall. See the picture below for location.


Diagnosis:
Warning: Make sure your engine is cool. You will be touching and working with metal components close to the engine and there is a potential to burn yourself on hot surfaces!
1. Before removing anything, reach up under the EGR valve "head" or disc like shape and push upwards on the diaphragm which is a flat surface located at the center of the valve housing. This should freely move up and down (with some spring back force). If it doesn't, your valve is clogged to the point that it cannot actuate. You can skip the rest of the diagnosis because you will need to remove it to clean or replace it.


2. Remove the passenger side hose using a flat-head screwdriver to assist in sliding the hose off.
3. This step will test the ability for the EGR valve to hold a vacuum. Push the diaphragm up as far as it will go and then place and hold your finger over the opening on the stem that the hose was just removed from. While keeping pressure on the stem opening, remove your fingers from applying upward pressure to the diaphragm. The diaphragm should stay where it is and when you now remove your finger from covering the hole it should snap into place. Do this multiple times to confirm that the EGR valve holds a vacuum. If the diaphragm returns to it's original position prior to uncovering the hole opening then the EGR valve needs to be cleaned or replaced.

Here is a great video on how to remove/replace the EGR as well as check that it holds a vacuum. Skip to 9:00 for the vacuum diagnosis test.

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