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Guest Message by DevFuse

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OBD II EGR flow malfunction P0400

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5 replies to this topic

#1 mspeters


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Posted 20 October 2004 - 11:50 AM

I recently bought a 98 OBW 2.5L 5sp w/ 160k.
It had a check engine light with the following faults:
P0400 EGR flow malfunction
P0304 Cyl 4 misfire
It also idles low/rough once it is warmed up.

I revved (sp) the engine to 3000 a few times and the EGR did actuate; also the diaphragm holds vacuum. I took the EGR off and cleaned it w/ carb cleaner and it still has the problem. My gas mileage is only 25mpg, but it drives great other than that.

Before I go replacing parts, is there anything that I have overlooked? Is there a temp sensor in the circuit that I can check? The Haynes manual doesn't help much beyond what I have tried. (It's worth the $14 I payed for it, not much more...)
Thanks in advance for any help / suggestions.

#2 Setright


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Posted 20 October 2004 - 12:21 PM

Two temp sensors, one for the dash gauge and one the ECU. Obviously, its the second one that counts in this case. They are located right next to eachother in the pipe that collects coolant from the top of the engine and feeds it to the radiator.

Search around the site, there are lots of references and photos to get smart with ;-)

#3 Commuter


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Posted 20 October 2004 - 04:27 PM

I dealt with P0400 for about a year in total on my 97 OB. Royal PITA...

They first replaced the little diaphram device that sits right up top. The diaphram was torn they said. Still got the code.

Next, they bypassed the little vacuum tubes under the throttle cable, but that was not the problem.

Then, they changed some solenoid (I don't even know where the thing is, I wasn't able to readily spot it). Now my code is finally gone.

During all this time (I was clearing the code almost daily), I did get P0304 once. Not sure why. It never reappeared. But the EGR is hooked up to the intake runner that feeds cylinder 4, right? (I hadn't thought of that before...)

Oh... one other thing. When I first got this code a couple of years ago, it had nothing to do with the EGR system itself. There is a small pressure sensor mounted on the passenger strut tower. It has some input to the auto tranny shift algorithm. In addition, it "checks" the EGR function. This sensor had failed on my car. I had noticed slighty delayed sloppy shifts at times. After this sensor was changed, the shifting returned to normal. I see yours is a 5 speed, so I don't know if this sensor exists or not on your car.


#4 mspeters


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Posted 13 January 2005 - 03:04 PM


cyl 4 misfire caused by...drum roll..........head gasket failure!

The shop I have looking at it is Georges Foreign Car Service in Grand Rapids, MI

they quoted me $850 in labor. I ordered parts from 1stsubaruparts.com for $150.

long shot, I know, but does anyone have any experience dealing with any shops in West Michigan?

I was refered to these guys from a friend, but I still wouldn't mind hearing where else people have gone...

Is the antifreeze additive for 98 MY as well?

#5 NoahDL88


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Posted 13 January 2005 - 06:33 PM

I grew up in K-Zoo, but i moved out before i got into subarus, i dont know much about the subaru dealerships on that side of the state, but there is maple hill subaru off 131 on M43 i believe. this may be blasphemy but try www.Nasioc.com there sure to have more people from michigan, the older subarus just didn't last out here cause of our love affair with salt.

#6 mspeters


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Posted 04 February 2005 - 01:17 PM

Got my OBW back yesterday. Runs better than ever!

After 70-80 mi I got a CEL for EGR Flow malfunction (P0400) back again. The Headgasket replacement (and exhaust vlv replacement - large crack from edge to base) fixed the cyl 4 misfire.

Are there any diagrams / algorithms that a dealership or SOA have that show what the ECU checks each time for CEL's?

What a tool that would be!

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