P0401 EGR insufficient flow.... cant figure out...
06-07-2018, 01:56 PM
#1
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P0401 EGR insufficient flow.... cant figure out... 1999 Z28 w/60,000 miles
Cleaned both EGR lines and replaced EGR valve.
Diagnostics show EGR voltage between .5 (idle) and 4.4 under normal driving around neighborhood. After reetting DTCs the first trip gets a P0401 (pending fault) and a service engine light lit on the dash. What should I try next?
Cleaned both EGR lines and replaced EGR valve.
Diagnostics show EGR voltage between .5 (idle) and 4.4 under normal driving around neighborhood. After reetting DTCs the first trip gets a P0401 (pending fault) and a service engine light lit on the dash. What should I try next?
06-07-2018, 02:04 PM
#2
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One question- Is EGR required to pass smog in your state? If so, then carry on. If NOT, then remove the system and tune around it. Your engine will thank you!
06-07-2018, 02:12 PM
#3
Remove the EGR and start the car. Is there a lot of exhaust flow? Is there a large vacuum flow to the intake? If either pipe doesn't have a ton of flow you have a restriction.
If both pipes flow really good, try another EGR, warranty swap it.
How good are the 02 sensors? These cars use the 02's to see the rich mixture come in after EGR activation to verify EGR is working, and I believe it uses the MAP sensor also looks for the change in kpa in the intake. Some cars have egr flow sensors that could cause your issue, but these do not.
If both pipes flow really good, try another EGR, warranty swap it.
How good are the 02 sensors? These cars use the 02's to see the rich mixture come in after EGR activation to verify EGR is working, and I believe it uses the MAP sensor also looks for the change in kpa in the intake. Some cars have egr flow sensors that could cause your issue, but these do not.
06-07-2018, 02:19 PM
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Remove the EGR and start the car. Is there a lot of exhaust flow? Is there a large vacuum flow to the intake? If either pipe doesn't have a ton of flow you have a restriction.
If both pipes flow really good, try another EGR, warranty swap it.
How good are the 02 sensors? These cars use the 02's to see the rich mixture come in after EGR activation to verify EGR is working, and I believe it uses the MAP sensor also looks for the change in kpa in the intake. Some cars have egr flow sensors that could cause your issue, but these do not.
If both pipes flow really good, try another EGR, warranty swap it.
How good are the 02 sensors? These cars use the 02's to see the rich mixture come in after EGR activation to verify EGR is working, and I believe it uses the MAP sensor also looks for the change in kpa in the intake. Some cars have egr flow sensors that could cause your issue, but these do not.
Pre cat are normal and fine.... post cat have cheaters on them for !cat. Its been that way for a decade and hasn't caused me any trouble.
Update: I cleaned the old EGR valve and put it back on. it reads .9 at idle. maxes out at about the same. First drive did not set off a pending code. Wondering if i just got a bad replacement valve.
06-07-2018, 03:19 PM
#7
Which O2's are used in conjunction with the EGR? Pre cat/post cat? Both?
Pre cat are normal and fine.... post cat have cheaters on them for !cat. Its been that way for a decade and hasn't caused me any trouble.
Update: I cleaned the old EGR valve and put it back on. it reads .9 at idle. maxes out at about the same. First drive did not set off a pending code. Wondering if i just got a bad replacement valve.
Pre cat are normal and fine.... post cat have cheaters on them for !cat. Its been that way for a decade and hasn't caused me any trouble.
Update: I cleaned the old EGR valve and put it back on. it reads .9 at idle. maxes out at about the same. First drive did not set off a pending code. Wondering if i just got a bad replacement valve.
sounds like you figured it out
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06-08-2018, 10:27 AM
#15
TECH Senior Member
Apparently, since the only "test" is plugging into the OBD2 port, the computer has to "see" the EGR system being intact, but somehow does NOT have to see the rear O2 sensors correctly functioning?? Because W/O converters, they will NOT be reading correctly!
06-08-2018, 11:28 AM
#16
OP said he had cheaters in the rear o2's so he needs to go get it tuned and disable rear o2's, egr, and air injection and take all that off.
