Results 1 to 13 of 13

Thread: 6.5 diesel egr flow insufficient codes

  1. #1
    Join Date
    Nov 2017
    Location
    New York
    Posts
    5

    Default 6.5 diesel egr flow insufficient codes

    I'm new here to the forum and I have a question about my 98 YMCA sierra 2500 2wd with a 6.5 diesel. Every time I drive the truck I get a P0400 and P0501 code for Egr flow and Egr flow insufficient. The truck is all stock other than I cut the muffler and converter off and put flex pipe on instead. I have done a few tests and I have vacuum to the first two black solenoids on the drivers side while the truck is ideling but I'm not getting any vacuum coming out of the middle solenoid. I checked all the vacuum lines and none of them are collapsed and they all look good. Does anyone know why I keep getting these codes. They come on after 20 or 30 minutes of driving and is it possible the codes are on because I removed the converter and muffler? Any help would be greatly appreciated.

  2. #2
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,057

    Default

    Cutting the converter off probably reduced the back pressure and hence flow through the EGR system, enough to cause the code. The code might not affect performance, so, unless you have an inspection problem, it could be ignored. (Check the service manual to confirm this.)
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  3. #3
    Join Date
    Nov 2017
    Location
    New York
    Posts
    5

    Default

    Is there a back pressure sensor? If so is there a way to trick the computer into thinking it's fine. There is a noticeable loss in performance when the codes come on.

  4. #4
    Join Date
    Jan 2005
    Location
    Denville,New Jersey
    Posts
    424

    Default

    Have these codes been there before the modification, or have they always come up? The solenoids are not very expensive and the EGR valve is easy to clean. I have had to replace a couple of them that held vacuum. I had the muffler and catylast off mine for a short time, and the computer didn't care. The reason I put them back was because there was no increase in mileage or performance, and I preferd a quieter engine sound.
    94 Chev Blazer, 6.5TD, 3.42, 4WD,Gear drive,,Remote FSD behind drivers headlight,,Mobil 1 in difs and trans,Rotella 30W, Over a quarter of a million miles !! Member -1.94 club.

  5. #5
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,057

    Default

    There's a mass airflow sensor on the intake. I'm not up on the particulars of the ODB II but I suspect if the airflow is not within certain parameters in assumes the EGR flow is responsible.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  6. #6
    Join Date
    Nov 2017
    Location
    New York
    Posts
    5

    Default

    The codes have been coming up before muffler and cat removal but they seem to come on sooner since removal. Does anyone know if I should have vacuum coming out of the middle solenoid while the truck is ideling. I have plenty of vacuum going into the middle solenoid or at the right fitting but no vacuum coming out or at the left fitting

  7. #7
    Join Date
    Dec 2003
    Location
    Yukon Canada
    Posts
    1,612

    Default

    Hi
    Seeing you are already "testing" without the cat and muffler...
    I would "test" with the EGR system removed...

    My.05 cents,i'm from Canada and we don't have penny's
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  8. #8
    Join Date
    Nov 2017
    Location
    New York
    Posts
    5

    Default

    So you would suggest taking off all the vacuum lines and electrical connectors and sensors? Wouldn't this throw even more codes

  9. #9
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Arrow

    Quote Originally Posted by gardentractorworld View Post
    So you would suggest taking off all the vacuum lines and electrical connectors and sensors? Wouldn't this throw even more codes
    Yep. Just find another ECM of the same year/model as your truck, only from a 2500HD (8600 GVWR, F code) or 3500, or purchase a reprogram. The computer is already complaining. Save yourself a lot of headache and eliminate the problem.*

    *This advice is for off-highway and diagnostic testing purpose only. It is unlawful to modify the emission system of any vehicle.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  10. #10
    Join Date
    Jan 2005
    Location
    Denville,New Jersey
    Posts
    424

    Default

    Have you had the egr valve off for cleaning? They fill up with a huge amount of carbon on mine. Besides, who is to say that the Canadian govt might change the law and now all your smog parts are missing.
    94 Chev Blazer, 6.5TD, 3.42, 4WD,Gear drive,,Remote FSD behind drivers headlight,,Mobil 1 in difs and trans,Rotella 30W, Over a quarter of a million miles !! Member -1.94 club.

  11. #11
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,382

    Arrow

    Quote Originally Posted by gardentractorworld View Post
    I'm new here to the forum and I have a question about my 98 YMCA sierra 2500 2wd with a 6.5 diesel. Every time I drive the truck I get a P0400 and P0501 code for Egr flow and Egr flow insufficient. The truck is all stock other than I cut the muffler and converter off and put flex pipe on instead. I have done a few tests and I have vacuum to the first two black solenoids on the drivers side while the truck is ideling but I'm not getting any vacuum coming out of the middle solenoid. I checked all the vacuum lines and none of them are collapsed and they all look good. Does anyone know why I keep getting these codes. They come on after 20 or 30 minutes of driving and is it possible the codes are on because I removed the converter and muffler? Any help would be greatly appreciated.
    P0400 - EGR Flow Malfunction
    P0401 - EGR Flow Insufficient
    P0501 - Vehicle Speed Sensor (VSS) Circuit Malfunction

    The only real component in the system that can monitor EGR flow is the MAF sensor. There is no differential EGR flow detector like those used with gas engines.

    So, the question is, what can cause EGR flow DTC codes?

    A bad MAF sensor.

    A bad vacuum pump or loss in vacuum (leaking lines/hoses), which means the EGR valve won't open.

    A bad EGR solenoid, which is a vacuum switch that controls the EGR valve.

    A bad turbocharger wastegate solenoid, which can affect incoming airflow over the MAF sensor.

    A plugged catalytic converter will restrict exhaust flow resulting in excessive backpressure in the exhaust system, which reduces the intake airflow read by the MAF sensor. Removing the cat/muffler could still produce EGR flow codes because the EGR system was calibrated to work as a complete system. A total loss of restriction would alter the flow dynamics.

    Always begin a troubleshooting process by carefully examining the related wiring and electrical connectors. Some these tests can be performed using a Tech II scan tool from the driver's seat. Might be worth the 1/2-1 hour of shop time at a dealership if the tech knows these diesels.

    Otherwise:

    1- Measure the vacuum.
    2- If vacuum pump and lines are OK, replace EGR solenoid.
    3- If that didn't help, replace wastegate solenoid.
    4- If that didn't help, measure exhaust system pressure differential across the catalytic converter to determine whether the cat is plugged. Replace cat if above about 3-psi at WFO (a hard run). Test this by drilling a 1/8" hole in the exhaust system right before/after the cat, install pressure fittings, do pressure test, then weld holes closed if pressure is OK. Most cats slowly plug over time. A few years of driving is enough to completely plug a cat when the vehicle is lightly driven in cooler climates.

    Jim

  12. #12
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    When the EGR valve opens you are recycling so the ECM expects a reduction in MAF readings. With the exhaust opened up there is slightly less back pressure, greater gross flow and less EGR flow.

    This can all be taken care of in the ECM programming.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  13. #13
    Join Date
    Nov 2017
    Location
    New York
    Posts
    5

    Default

    I haven't cleaned the egr valve yet it didn't look that bad. I was assuming it had something to do with taking off the cat and muffler.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •