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How to test EGR solenoid vacuum valve
Topic Started: May 13 2011, 05:12 PM (8,541 Views)
ogoz23
Elite Member
[ *  *  *  *  * ]
Well the other day I got a code for p0400 EGR flow I took the EGR apart and clean it very very well and so did the passages I have good exhaust flow and very good intake when the EGR was taking off , but I got the same code again today I check the EGR if it opens with a vacuum and the diaphragm opens and if I hold the vacuum with my tongue (yes I know disgusting) the diaphragm stays open so I figure EGR pass the test the next test is the silonoid vacuum valve what's the proper way of checking this ? :drool
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rdcouch
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I would like to know as well, I've been searching this forum relentlessly and the EGR FAQ thread doesn't help. Same situation, with the EGR off one hole blows out exhaust and the other has vacuum. EGR valve itself is new and opens and closes when revving the engine. I also tried bypassing the pressure transducer thing and noticed no difference is how the car ran at idle or revving it up, I'm not sure if that indicates if the pressure transducer is good or bad. So my p0400 is either being tripped by that, or the solenoid and need to know how to test it.
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Big Rhino
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Disconnect vaccum and electrical connectors. With DVOM check for continuity between the electrical contacts and body. If continuity is on either terminal, replace the valve. Measure resistance between terminals. Should be between 33 and 39 ohms. If not, replace the valve. Blow air into port number 2. Air should blow out of airfilter and not out of port number 1. If so replace the valve. Apply battery voltage and a ground to the electrical terminals. With it energized, blow air into port 2. Air should blow thru port 1 and not out of air filter. Port 2 is the port that points the same direction as the electrical connector.

Welcome to the forum rdcouch.
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mwebb
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FOG

i have been very busy and not looking here so ....
the EGR uses a separate solenoid for testing .... even if the EGR works well the TEST circuit may be fraked up i will put up a detailed post this weekend regarding testing for it

do not use an ohm meter on broken cars

you will need a long length of plastic tube about 3/32" id and a vacuum T and a vacuum gauge so that you can connect into the TEST vacuum circuit of the EGR , not the normal operating circuit of the EGR

the TEST circuit does not use the back pressure transducer, the TEST circuit uses the other solenoid
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Big Rhino
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mwebb
May 15 2011, 09:20 AM

do not use an ohm meter on broken cars

Rediculous! Your cars electrical system and componets use voltage and amperes and wiring that can be checked for continuity. DVOMs are made for this purpose. Factory service manuals as well as other repair manuals give you illustrated test to perform with DVOMs in the repair of such electrically driven circuits. Heres one ASE mechanics take on it from a simple google search,

http://motorage.search-autoparts.com/motorage/article/articleDetail.jsp?id=583957


.
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mwebb
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FOG

enginedoctorgeo
May 15 2011, 11:15 AM
mwebb
May 15 2011, 09:20 AM

do not use an ohm meter on broken cars

Rediculous! Your cars electrical system and componets use voltage and amperes and wiring that can be checked for continuity. DVOMs are made for this purpose. Factory service manuals as well as other repair manuals give you illustrated test to perform with DVOMs in the repair of such electrically driven circuits. Heres one ASE mechanics take on it from a simple google search,

http://motorage.search-autoparts.com/motorage/article/articleDetail.jsp?id=583957


.
guess what ?
those manuals and those alleged techs are all WRONG , the manuals will all end at
"replace ECM with Known good Part " and guess what , pbbbt it is false

i ran a GFF test last week on V157 G336 assembly in a VW and it ended at , "replace V157 / G336 assembly" ,the GFF tests were all ohm meter based guess what ?
that was wrong , the fix was completely unrelated to anything that could have been obtained with ohm meter testing and
that is typical -

voltage drop testing on loaded circuits will actually locate real problems , ohm meters should never be used on broken cars .
the ECM does not see resistance , it sees voltage or frequency , unloaded circuits DO NOT as in CAN NOT show accurate test values
your ohm meter CAN NOT and DOES NOT load circuits , circuits that are NOT tested under load are NOT BEING TESTED ACCURATELY

not too difficult to understand .
===================
moving right along
without your ohm meter ... bring your brain to work .

verify that holding the throttle open at about 2k rpm will open the EGR valve , you will see the diaphragm move , if not
bypass the EGR back pressure transducer and repeat , does the EGR valve move now ?

it just happens that my system coded ,
Posted Image
P0400 - that is where i am right now , i have just bypassed my EGR back pressure transducer and now the EGR diaphragm opens at 2k rpm , hot engine ,Posted Image it did not open with EGR back pressure transducer connected as designed, so i dumped DTCs .
even with the P0400 all my monitors had run and passed .... including the EGR monitor .....
Posted Image one EGR test passed , one did not
more information http://service.gm.com/gmspo/mode6/pdf/Metro_Tracker/1996MY_Metro_1.0L.pdf

i did not have any test equipment with me , except the laptop and scan tools software , tomorrow i will see why the EGR back pressure transducer was not passing any vacuum to the EGR diaphragm . last summer , it did under those same conditions .

=============================
un related to the EGR problem .... since the scan tool was connected anyway ...
new Escan update
the older version will do this too
this is measured / actual verses calculated air flow through the engine , pretty accurate under heavy load but at cruise , the MAP sensor is over reporting , which will result in less ignition timing advance than is optimal .... at cruise or 43 mph here .
Posted Image

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mwebb
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FOG

to test either EGR solenoid
key on engine off , disconnect the solenoid connector ,
Posted Imageuse t pins

one pin will have 12 volts positive , the other will have ,
nothing
reconnect the solenoid , install a T pin
Posted Imagein the solenoid connector with nothing

install a vacuum line on that solenoid and blow through it , as you apply ground or 12 volts negative to the pin with nothing ,
the solenoid should click and the solenoid should change state , if it was open and flowing it should close and stop flowing , if it was closed , it should open and allow flow , you should be able to connect and un connect ground to the pin , each time you connect and un connect ground , the solenoid must change state

if yes , the solenoid is good and the positive connection to it is good as well

if not
the solenoid is bad , or you have a voltage drop on the positive side , connect your DVOM using a T pin to the positive side while grounding the other side , if voltage stays 12 volts or above , the solenoid is bad

you still could have a voltage drop on the switched side , the side with nothing .
so if you are this far with a good solenoid but still have a DTC P0400 , connect DVOM negative to battery negative and DVOM positive to the pin that had nothing as per earlier testing ,
you will need to drive the car at light cruise , about 45 mph on a flat level road , have your co pilot observe the meter
when the ECM activates the EGR , the value you see on the DVOM must not exceed 100 millivolts or
.1 volts if it does , there is a bad ground for the ECM .
the DVOM will show system voltage , about 14 volts until the ECM activates the EGR

there are two solenoids , the test solenoid only operates in DFCO see the GM MODE 6 link and read under the EGR section -

this can be a bit intimidating for the rookies , but
it is not as hard or confusing as it may seem , use a co pilot , keep your wits about you and do not get stressed about it
it can actually be fun . it's what i do .
=======================================
get the long vacuum line and vacuum T and vacuum gauge ready .... there is another way to test EGR solenoids, without using a DVOM or T pins , until you find a problem .

Edited by mwebb, May 16 2011, 11:28 PM.
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georandy
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:whistle :popcorn
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