EGR Flow Malfunction, and sometimes a Cylinder 4 Misfire.
My 1997 Subaru Outback is throwing a P0400 CEL code, along with a P0304 CEL Code. It drives perfectly fine, but on start-up after sitting for a couple hours, the subie sounds like its gasping for air or something. About 2 weeks ago, I was running low on coolant and didnt know it, so my engine maxed out at 288 degrees F before the coolant started leaking/ exploding. Thats when all these other problems started. First I just got the P0400 CEL Error Code --> which is an EGR Flow Malfunction, and recently, I'm also getting a P0304 CEL Error Code --> which is a cylinder 4 misfire. I think the EGR Flow Malfunction has something to do with that one. Any ideas or good sites to check out?
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Re: EGR Flow Malfunction, and sometimes a Cylinder 4...
How does the oil look? Is it milky or is there any discoloration? Is any moisture or steam vapor coming out of the exhaust pipe? The EGR fault is most likely being triggered from the cylinder missfire. Sounds like you might have a head gasket blown, and/or a cracked or warped cylinder head from the overheating. You can run a compression test to help determine this. Good luck...i hope this helps you troubleshoot the problem.
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code p0400 refers to exhaust gas recirculation(EGR) system---flow malfunction.===causes---hose leak/blockage--basic setting not carried out (if applicable)---wiring---EGR valve ---EGR solenoid---ECM
check out the valve and solenoid.
You'll have to get someone to check the spark and injector on cylinders 3 and 4. Code 303 is for loss of power on cylinder 3 and code 304 is the same for cylinder 4. The most common causes are lack of spark or fuel. Once the problems are fixed the codes will need to be erased with a scanner or code reader.
P0400 - Exhaust Gas Recirculation Flow Malfunction The exhaust gas recirculation (EGR) valve is vacuum controlled valve that regulates the amount of exhaust gases that re-enter the cylinders. The powertrain control module (PCM) determines how much based on engine load, temp, and other conditions. If the PCM detects that the amount of exhaust gases entering the cylinder were insufficient or non-existent, this code is set.
No symptoms will likely be noticed by the driver other than the MIL (malfunction indicator lamp). However, non visible symptoms will be increased combustion temperature and increased Nox emissions. A code P0400 may mean that one or more of the following has happened: - Plugged EGR passage which restricts the flow of exhaust gasses - Faulty EGR solenoid - Faulty EGR solenoid wiring/harness - Vacuum lines damaged/disconnected to the EGR valve solenoid or to the EGR valve - Faulty EGR valve
My advise is to look at what moistcabbage had to say about your problem. Then I will add a little advise:
Put the P0171 on hold until you have a verified fix for the other 2 codes. Here's why:
A misfire causes raw fuel and air to be shoved down the exhaust as an unburned mixture (After all. that's what a misfire is.) This can cause the free oxygen level in the exhaust to rise and cause the lean code (P0171) From the EGR code that you have, I can tell that you have the 2.0L engine in your car. (This is not a valid code for the 2.5L) In this case, moistcabbage is sort-of correct. Thiscode actually indicates that the EGR valve does not move when the computer commands the EGR to open. (Which SHOULD also be producing a P0400 code, which is EGR no or low flow.) If P0400 is not present, then chances are that this is caused by the EGR sensor "lying" to the computer and telling it that the EGR is not opening when it really is. However, it also may be telling the truth and the computer just hasn't picked up on the low flow issue yet. Anyway, if the EGR is not moving, it could be caused by a vacuum leak, which will also cause your P0171code.
The logical order of this would be to check for obvious causes of misfire like the spark plug, wire, coil, and fuel injector and correct as necessary. Also check the EGR system out to find out what the cause of the EGR not moving code is. (And repar as necessary) Then clear the codes and drive the car to see if the P0171 code returns. If P0171 returns and the other codes stay gone, then you will have to check into oter possible causes of the lean code. Otherwise, I would not waste any time checking into a lean condition at all before the other two codes are confirmed fixed.
DTC P0400 - Exhaust Gas Recirculation Flow Malfunction The exhaust gas recirculation (EGR) valve is vacuum controlled valve that regulates the amount of exhaust gases that re-enter the cylinders. The powertrain control module (PCM) determines how much based on engine load, temp, and other conditions. If the PCM detects that the amount of exhaust gases entering the cylinder were insufficient or non-existent, this code is set.
No symptoms will likely be noticed by the driver other than the MIL (malfunction indicator lamp). However, non visible symptoms will be increased combustion temperature and increased Nox emissions.
A code P0400 may mean that one or more of the following has happened: Plugged EGR passage which restricts the flow of exhaust gasses Faulty EGR solenoid Faulty EGR solenoid wiring/harness Vacuum lines damaged/disconnected to the EGR valve solenoid or to the EGR valve
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The OBD II code for P0400 is Exhaust Gas Recirculation Flow Malfunction.
I'm sure the only thing you have left is you may have to replace the EGR valve or check for any leak from the vaccum lines going to to EGR valve.