95 GXE Knock Sensor and/or EGR valve

[urbanphil]

I've had a check engine light for a few days. Autozone was able to scan my CPU despite the fact that my GXE is a 95. 2 codes came up--P0400, for the EGR, and P0325, for the knock sensor, which it turns out is a $180 part. Anyone have this problem? If so, do you have any clever ideas that could help me avoid dropping 2 bills on this part. thanks, Phil

[JustSayGo]

Maybe the EGR function code is a blocked vacuum hose or blocked at the throttle body. Are the EGR temperature sensor wires unplugged? After the EGR problem is corrected reset the ECU and see if the light comes back on. If you still have a knock sensor code, new OEM sensors are under $100 incl. shipping.

https://www.rockauto.com/applet3.html

[urbanphil]

Originally Posted by JustSayGo

Maybe the EGR function code is a blocked vacuum hose or blocked at the throttle body. Are the EGR temperature sensor wires unplugged? After the EGR problem is corrected reset the ECU and see if the light comes back on. If you still have a knock sensor code, new OEM sensors are under $100 incl. shipping.

https://www.rockauto.com/applet3.html

I took the EGR valve off & cleaned it--there was quite a bit of carbon gumming up the works. The hoses don't seem to be plugged. It's now running better but the light is still on. Is there some trick to reseting the ECU besides unhooking the battery. thanks, Phil

[JustSayGo]

The ECM is in the center console under the radio. There is a hole in the plastic console cover near the accelerator pedal to use a straight blade screw driver to turn a plastic screw in the ECM. If it has never been reset manually before, there is cellophane tape that covers the screw. It may be easier to remove the little section of the console near the accelerator so that you can see the ECM and the screw.

Break through the tape. You don't need to replace the tape when your finished.

With the ign switch turned on but eng not running, turn the screw clockwise until you feel the stop and then turn it counterclockwise until it stops. This will erase the codes from the ECM.

I think the code indicates that the EGR valve is not moving. There are several possibilities. Check each of these. The higher combustion temperature may be causing a fuel knock so that the Knock Sensor retards the timing (before you even hear the knock) so far that it sets the Knock Sensor code. Follow theses diagnostic steps.

The EGR uses a small amount of exhaust metered into the combustion chamber to cool off the fire similar to the way that a fire extinguisher puts out a flame. Both the exhaust gases and what ever is used in the particular fire extinguisher don't have oxygen and displace air that does have oxygen to slow down or control the flame.

Does the engine run rough at idle if you put vacuum to the EGR valve? Either the exhaust to the EGR valve is plugged or there is no vacuum going to the EGR valve.

The repair manual says that there is a slit machined into the throttle body that can get blocked and stop the vacuum signal that is used to open the EGR valve.

Have you checked the EGR valve diaphram for a vacuum leak?

Have you checked the vacuum hose from the EGR valve to the canister to see if they hold vacuum and that the canister solenoid valve doesn't leak vacuum and opens to let vacuum through?