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CEL Code P0400


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23 replies to this topic

#1 Bill_96OBW

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Posted 01 December 2003 - 08:16 PM

I know emissions problems can be very hard to diagnose but I would appreciate any suggestions here. I have a 96 OBW, well maintained. At about 95k miles the check engine light came on for the first time ever. Code was P0400. The dealer replaced the EGR valve and booster valve (back pressure) and cleared the codes. 10 days and 300 miles later the CEL came back on, same code. Dealer said passages were dirty and spray cleaned the exhaust gas regulations and cleared the engine control unit. 10 days and 330 miles later the CEL is back on, same code. The dealer checked with Subaru and cleaned the exhaust gas regulations again with a wire this time to clear any buildup. CEL is off but I am not sure for how long. The dealer has only charged me for the initial visit but I am tired of going back.

So any ideas, or is this the correct fix? Is there any problem driving with the CEL on. We are planning a 700 mile trip to Chicago at Christmas.

Thanks for any suggestions here.

#2 alias20035

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Posted 01 December 2003 - 09:46 PM

Originally posted by Bill_96OBW
I know emissions problems can be very hard to diagnose but I would appreciate any suggestions here. I have a 96 OBW, well maintained. At about 95k miles the check engine light came on for the first time ever. Code was P0400. The dealer replaced the EGR valve and booster valve (back pressure) and cleared the codes. 10 days and 300 miles later the CEL came back on, same code. Dealer said passages were dirty and spray cleaned the exhaust gas regulations and cleared the engine control unit. 10 days and 330 miles later the CEL is back on, same code. The dealer checked with Subaru and cleaned the exhaust gas regulations again with a wire this time to clear any buildup. CEL is off but I am not sure for how long. The dealer has only charged me for the initial visit but I am tired of going back.

So any ideas, or is this the correct fix? Is there any problem driving with the CEL on. We are planning a 700 mile trip to Chicago at Christmas.

Thanks for any suggestions here.



It should be ok.... If they properly cleaned it on the third trip.

Odds are it was a plugged EGR line and not a valve problem. They should have cleaned the line properly the first time, there is even a special "scrubbing" tool to do this, it is a round nylon brush on a long flexible shaft. You take the EGR pipe off and run the scrubber through a few times with some cleaner fluid.

I had to clean the EGR pipes on my old 85 Subaru about twice as often as I had to clean the EGR valve assembly.

You can drive with the CEL on, its just not recommended that you do so for a long period of time. If the CEL comes on again, it will most likely be for the EGR again. An EGR problem will cause some cold operations problems (only at 0 F or below), and slightly higher fuel consumption and emmisions, but you are not going to hurt anything. If the CEL light comes on again in three weeks (Christmas) have it diagnosed though, the EGR CEL should return in the next week if this particular problem is still present, but an CEL three weeks from now could be something different.

#3 Commuter

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Posted 01 December 2003 - 11:29 PM

I have a 97 OB and have the same code right now. I just haven't gotten around to taking it back to the dealer. I just keep reading and clearing the code.

However, I had this happen in the spring this year (same code). I have an auto. It turned out to be a little pressure sensor (more of a manifold vacuum sensor actually) that mounts on the passenger strut tower. It "checks" the EGR by looking for a change in pressure when the EGR is activated. In my case, it was this sensor that was failing.

The sensor has some purpose as an input to the TCU. I had noticed that my shifts were a little "off". Bit sluggish, almost as if something was slipping at times. I thought I had some transmission problem developing, but it was the sensor. My shifts went back to normal after it was changed. And the EGR code went away (until now that is).

Be forewarned... it's an expensive little sucker! :eek:

Just another possible source of the PO400 code.

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#4 Bill_96OBW

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Posted 02 December 2003 - 07:54 PM

Thanks for your replies. The check engine light is back on after one day and 50 miles. I'm going back to the dealer in 2 days but they admit they are not sure what to do next. I will share the sensor info with them and we will try again. By the way my 96 OBW is an automatic but I haven't noticed any shift changes.

Maybe all I need is some black electrical tape to cover the light since I don't know how to turn it off. I was told that disconnecting the battery will not work for 96 and newer.

I'll update as I learn something new.

#5 99obw

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Posted 09 December 2003 - 08:38 PM

What did you find out?

My wife came home tonight and informed me that the check engine light was on. I pulled a code P0400. :boohoo:

#6 PAezb

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Posted 09 December 2003 - 10:19 PM

Just to add my final experience, it appears I finally got rid of the returning CEL and P0400 by replacing the Back Pressure Transducer - $48 + shipping from 1stsubaruparts.com.

I had previously replaced the EGR Soleniod, cleaned the vacuum lines and EGR valve, replaced the EGR gasket and vacuum hoses, all with no affect.

Now with several hundred miles since the BPT replacement, no returning CEL. :banana: Keeping fingers crosssed.

Hope you all with the P0400 code can get it resolved soon. That CEL light is sure annoying to have glaring at so frequently and for long periods. I almost resorted to pulling the bulb from the instrumentation cluster.

I'm in love with my Subie again....::)

Paul
96 OBW/2.5 auto 130K miles

#7 Bill_96OBW

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Posted 10 December 2003 - 12:12 AM

The story continues, hopefully with a happy ending. On the fourth trip to the dealer the tech's theory was that a small piece of carbon was still loose in the system. He has 20 years experience in emissions and he was frustrated too. He cleaned everything again and asked if he could keep the car overnight and drive it home and on a long test drive. He drove it 172 miles and no returning light. I am now at 500 miles with no light. The dealer, Russel Subaru, has been great here. There was only the initial charge to replace the EGR and back pressure valves, plus they gave me a free loaner, a 2003 Baja, while they kept my car. Dealers get a bad rap many times but I highly recommend Russel to anyone in Maryland. These emissions codes can be tricky but they worked with me to get it fixed.

#8 99obw

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Posted 10 December 2003 - 06:21 PM

I cleared the code last night and it hasn't returned. When my wife told me about it she mentioned that she had just filled the gas tank. I asked her if she tightened the cap until it clicked. She said "ummmmmmmm, I don't know". It was a little loose, maybe a 1/4 turn before it clicked. I am hoping that was all it was, but knowing my luck I will need every part in the system. :rolleyes:

#9 99obw

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Posted 02 February 2004 - 08:12 PM

Well, the outback had another MIL tonight, P0400. :banghead:

I cleared it and I am going to wait and see.

#10 Commuter

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Posted 02 February 2004 - 09:19 PM

When I first started getting mine... it was a few weeks between the CEL's showing up. After a few months, it was coming on almost daily.

I had the car in recently. They said there was a tear in the diaphragm. Unfortunately, it would appear that is not all that is wrong. 24 hours later, the CEL was back and it keeps coming back almost daily.

It's been too cold for me to mess with it. I'll just keep clearing it until I get to it, or get back to the dealer.

PITA... :( I'm glad Subaru got rid of this system on the Phase II engine.

Commuter

#11 subyroo

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Posted 03 February 2004 - 07:37 AM

Does anybody have an idea on what this code means on a 99 Forester with 118k on the clock:

P420 - Catalyst Efficiency Below Threshold.

Is this pointing me toward the Catalytic Converter or am I on wrong track?

#12 1 Lucky Texan

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Posted 03 February 2004 - 09:08 AM

more likely O2 sensors (at least the front one) if they've never been replaced.

#13 99obw

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Posted 03 February 2004 - 09:18 AM

Actually I think that would most likely be the rear O2 sensor.

#14 subyroo

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Posted 04 February 2004 - 12:28 AM

I found a thread on a F_F_F_F_Ford forum and it said that their P04020 code was the lack of comms between the front & rear 02 sensors. I will get my mate to check them both out.

Thanks for your replies fella's.

#15 99obw

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Posted 05 February 2004 - 08:42 PM

Well, the MIL is back on tonight. The saga begins....

#16 99obw

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Posted 06 February 2004 - 08:13 PM

I have decided to pull the EGR valve off and give it a good cleaning. I will also clean the pipe that runs from the left head to the EGR valve. Anything else I should clean or inspect while I have it apart? Any tips? I was thinking of hooking my mityvac to the vacuum port on the EGR and doing a leakdown test. The haynes manual actually has some decent information for the EGR that I am going to follow. I will look in the FSM too.

I went to the dealer today to get a new EGR valve gasket. The guy told me that the '99 doesn't show a gasket, but the previous years do. I bought the gasket just in case. It's a 14719KA000.

#17 99obw

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Posted 08 February 2004 - 12:40 PM

First of all, the '99 DOES have an EGR gasket, and the part number above is correct.

The haynes manual instructs to observe the EGR valve position while quickly advancing the throttle from idle to 2000-3000 RPM. When doing this I noticed that the valve would open and then close. I don't know if this is normal, the manual doesn't give specifics.

I pulled the EGR valve off. I did a leakdown and the diaphragm holds vacuum fine. There was a little condensation on the exhaust side of the needle. The passages look clean enough, I am going to leave them alone.

I pulled the back pressure transducer (BPT). The BPT has four ports. Three small vacuum ports labeled P, Q, and R, and one larger port described as the exhaust pressure (in subaru document titled "Basic Emissions and Fuel Systems, Module 405"). The subaru document basically shows the BPT as being an exhaust pressure controlled valve. The control diaphragm is between P and the exhaust pressure, and the flow between R and Q is controlled by another diaphragm that is connected to the other diaphragm by a rod.

The BPT seems totally hosed. When I blow in any of the four ports it comes out of the other three.

1stsubaruparts:

BACK PRESSURE TRANSDUCER, All Models, 2.5L 96-99 $47.87

I will call and check stock tomorrow.

Actually I am pretty happy, this may have been an easy fix. (fingers crossed)

#18 99obw

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Posted 12 February 2004 - 08:07 PM

I ended up going to the local dealer for the BPT. I installed it and the code is gone, at least for now.

When I was at the dealer the parts guy said that they always add an inline filter when replacing a BPT. The car is not originally equipped with one. The filter part number is 22663AA010. It is the same small white device with dark grey foam around it that can be seen near the IAC air supply hose on the right side top of the engine. That filter protects the sensor on the right strut tower that the vacuum line goes to. Apparently adding one of these filters inline with the solenoid, BPT, and EGR valve will protect them from moisture. The BPT valve I replaced was full of water, spraying out the ports when I blew into it. I will be adding one of these filters.

#19 PAezb

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Posted 17 February 2004 - 04:25 PM

Is that filter part number correct? - I couldn't find it on 1stsubarupart.com. Also, whats the ballpark price on that item?

Paul

#20 99obw

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Posted 17 February 2004 - 07:37 PM

22663AA010 FILTER ASSY PRESS SEN $10.29

Their website only shows the most common parts. I often just mention what I need in the comments section of the order page and Jason will call me if he has any questions. If you give him the Subaru part number it's even easier. I haven't installed the filter yet so I can't tell you exactly where it goes. I can take a look sometime soon.

FWIW the parts guy also said that a lot of times they just use a small lawn tractor type fuel filter. I couldn't bring myself to install one of those, so I paid the extra and bought the Subaru filter. Expensive little bugger.

#21 avk

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Posted 17 February 2004 - 07:42 PM

1stsubaruparts has exc. pricing and service, but uses a generic parts database from parts.com. It is something like Mitchell, and is incomplete and not always accurate. There are actually other dealers using the same parts engine, such as subarupartstore.com (with higher prices). Subaruparts.com seems to be the only storefront built on an actual Subaru database. It does recognize the p/n for this filter.

#22 PAezb

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Posted 17 February 2004 - 08:44 PM

Thanks for the replies. I checked with my local dealer and they want $18. I'll probably order a couple from 1stSubaru and replace the pressure side valve too. To make the order worthwhile, I may order a new bullnose protector. I lost my bullnose protector (Subaru's) tonight going through a carwash (through the blower/dryer). Tore the right side right off - 2nd one I've lost in the life of the car, a 96'. The first one I lost down in Texas on a single lane highway on a windy day and a passing semi-truck created such a vacuum that it just exploded the fiberglass/plastic? into a million pieces...all I could see was a smokey cloud of the bullnose falling to the ground in my rearview mirror. It was a cool effect but really pissed me off.

Why can't the manufacturer design decent mountings for the side edges of the hood? - those clips just don't cut it and that's where the problem is. Anyway, I guess I'll be looking up/or calling about the bullnose price on 1stSubaru as well.

Lemme see, where'd I put my wallet....

Paul

#23 99obw

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Posted 25 February 2004 - 07:46 PM

I installed the filter inline with the BPT tonight. I removed the vacuum line that goes from the "V" vacuum port on top of the throttle body to the "R" port on the BPT. I cut this line in two, removed and discarded about a 1/4" length of the line, and added the filter in the middle. This should produce the desired effect of somewhat protecting the BPT, solenoid, and EGR from moisture.

#24 rojo

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Posted 31 May 2011 - 10:45 AM

I just posted more info on a similar thread, but for folks having this problem, here's what my dealer found:

There's a Subaru tech tip dated June 2006 about CEL Code P0400 (EGR code). In following the recommended procedure, dealer found the hose connected to the MAP sensor was pulled loose at a "T" in the vacuum line.

Cheap fix!




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