EGR flow

[Bserk]

Geeze. I thought I was done bugging you guys for a while. 96 Legacy Outback, 2.5, A/T. She is up and running perfectly after a long winter of issues. Now I have a check engine light, code P0400, EGR flow....

 

With the car warm and idiling, opening the throttle causes the egr valve to open. If I manually open the valve with the car idling, it will practically stall the engine. This tells me the valve and its related vac. hoses and solenoids are working, and the egr passages are not plugged.....

 

 

 

Again, I apologize for falling back on my Nissan experiance, but this code is set on any OBD II era Nissan if the EGR temp sensor does not get a temp. change when the EGR valve is comanded 'on'. So I set out looking for a egr temp sensor..... I cant find one, on the car or in the wiring diagrams. So I guess my question is, how does Subaru 'decide' to set a egr flow code, and if I have a working system, what could cause this code to set?

 

I decided to licence this thing now, instead of waiting till Fall, and it wont pass NY inspection with the CEL on...and Ive tried resetting the light and getting the monitors to reset before the egr flow code comes back....no luck! This car hates me, Im convinced. LOL. any advice, again, would be very appreciated. Doug

[porcupine73]

Hello! Buffalo here. Service procedure first asks there are any other codes in addition to P0400. Then it says check for any leakage or clogging of vacuum hoses.

 

The most pertinent parts seem to be 'possibly egr valve malfuction may be due to freezing or clogging by foreign matter'.

 

'Is there any clogging in the gas outlets of intake or cylinder head, checking by breathing into the outlets?'

 

'do not use solvent when cleaning the egr valve assembly, as it can cause diapragm damage'

 

'replace egr valve as required'

 

There's some other more esoteric stuff about using the Select Monitor and some 'driving cycle'.

[OB99W]

Geeze. I thought I was done bugging you guys for a while. 96 Legacy Outback, 2.5, A/T. She is up and running perfectly after a long winter of issues. Now I have a check engine light, code P0400, EGR

flow....

I'm going to assume that's the only code you're getting. If there are others, please let us know.

 

 

With the car warm and idiling, opening the throttle causes the egr valve to open. If I manually open the valve with the car idling, it will practically stall the engine. This tells me the valve and its related vac. hoses and solenoids are working, and the egr passages are not plugged.....

It may well be that the EGR appears to be functioning correctly, but that when the EGR monitor is run something that OBDII uses to check it isn't "quite" right, setting the code. Some tests the ECU runs are done very quickly, and if a component reacts too slowly, it "sees" a fault. In addition to the EGR valve, there's its solenoid valve, and also a backpressure transducer; if one of the latter two are sluggish, it could be the problem.

 

 

Again, I apologize for falling back on my Nissan experiance, but this code is set on any OBD II era Nissan if the EGR temp sensor does not get a temp. change when the EGR valve is comanded 'on'. So I set out looking for a egr temp sensor..... I cant find one, on the car or in the wiring diagrams. So I guess my question is, how does Subaru 'decide' to set a egr flow code, and if I have a working system, what could cause this code to set?

 

I decided to licence this thing now, instead of waiting till Fall, and it wont pass NY inspection with the CEL on...and Ive tried resetting the light and getting the monitors to reset before the egr flow code comes back....no luck! This car hates me, Im convinced. LOL. any advice, again, would be very appreciated. Doug

Hook a scan tool up again; besides the code, it would be useful to get the freeze-frame data related to it.

 

I'd verify that the solenoid valve is opening fully and rapidly. You should be able to hear and feel a fairly sharp "click" if 12 volts is applied to the solenoid, and check that it's free-flowing.

 

By the way, I believe one of the parameters involved in EGR testing is the O2 sensor switching; under certain circumstances a marginal sensor might contribute to the problem, so monitoring it could be useful.

[sea#3]

The system is checked when driving at a constant throttle, and then the EGR is activated by the ECM through the solenoid valve. The ECM looks at the map sensor to look for a change in vacuum. If it does not see a change in 2 driving cycles it will activate the MIL

I’m sure the solenoid valve is working since you said that you can watch the EGR move when you snap the throttle but the test below can cycle the solenoid valve for a while , You can take a piece of vacuum line and blow through the valve while it is cycling, to verify that it is working properly

 

1) Turn ignition switch to OFF.

2) Connect the test mode connector. (Green connector under dash by gas pedal)

3) Turn ignition switch to ON.

: Does EGR solenoid valve produce operating sound?

NOTE: other solenoids and the a/c fans will cycle at this time

 

Another thing you should look at is the pressure sensor (map sensor)

It is on the right strut tower by the air filter, check the vacuum lines to it and make sure they are not blocked (make sure you check the filter if it has one in the line)

 

If that checks out there is a possibility the BPT (back pressure transducer) is intermittent

To check it I have found it’s easiest to hook a vacuum gauge teed off of the vacuum line to the EGR and drive the car

The following is the drive cycle it take to get the ECM to do the check

Drive at 88±5 km/h (55±3 MPH)

NOTE:

Keep the throttle valve opening at the same degree, since

diagnosis will be interrupted when the opening varies.

Diagnosis starts in 190 seconds after starting engine and

takes 4 seconds.

Put the gear to “D” range for the diagnosis.

Hope this helps

 

SEA#3

[Commuter]

The system is checked when driving at a constant throttle, and then the EGR is activated by the ECM through the solenoid valve. The ECM looks at the map sensor to look for a change in vacuum. If it does not see a change in 2 driving cycles it will activate the MIL ...

SEA#3

 

This map (manifold / atmospheric pressure) sensor was the problem in my 97 OB auto. It's a little black cube mounted on the passenger strut tower (towards the front of the car). Has some wires and vacuum line. The sensor was failing which was triggering the EGR code. I also noticed that my shifts were a little soft, or delayed at times. Apparently this sensor has some input to the tranny's shift algorithms. Once it was changed, both problems went away. Warning... it's an expensive little sucker. It can be tested, but I'm not up on multimeters and such.

 

If everything else is ok, I bet this is the culprit. I've heard of it happening to a few people.

 

Commuter

[porcupine73]

Yes the ECU/TCU use that signal to compensate pressures for high altitude use to reduce hard shifting. It's called map? Usually that means manifold absolute pressure used by the ECU in place of those sometimes finicky mafs.