96 OLDS Ninety Eight
EDG50
08-12-2007, 02:03 PM
I have PO401 OBD II error message I belive I have a bad EGR valve I need some info on how to check it! Or is this not the problem?
Blue Bowtie
08-12-2007, 07:10 PM
P0401 - Exhaust Gas Recirculation Flow Insufficient Detected.
The PCM believes the EGR valve is supposed to be open during deceleration, and expects to monitor a change in the MAP sensor as a result. If the EGR valve ot its passages are blocked with carbon deposits from the exhaust, detected flow may be inadequate.
You can remove the EGR valve easily by removing only the two mounting nuts. Set the valve aside, and carefully pass a stiff piece of wire (such as a cut coat hanger) through both sets of passages in the EGR mounting base on the engine. Continue to pass the wire through the accordion tubes toward both the exhaust manifold and intake manifold. Blow out or vacuum out each tube. You may even want to plug the passage for the intake manifold and start the engine, allowing exhaust pressure to blow out the exhaust tube. With the engine still running, uncover the port for the intake passage to see if vacuum is drawn through the port. Make sure the EGR valve pintle and base passages are clear as well. Install the valve.
The PCM believes the EGR valve is supposed to be open during deceleration, and expects to monitor a change in the MAP sensor as a result. If the EGR valve ot its passages are blocked with carbon deposits from the exhaust, detected flow may be inadequate.
You can remove the EGR valve easily by removing only the two mounting nuts. Set the valve aside, and carefully pass a stiff piece of wire (such as a cut coat hanger) through both sets of passages in the EGR mounting base on the engine. Continue to pass the wire through the accordion tubes toward both the exhaust manifold and intake manifold. Blow out or vacuum out each tube. You may even want to plug the passage for the intake manifold and start the engine, allowing exhaust pressure to blow out the exhaust tube. With the engine still running, uncover the port for the intake passage to see if vacuum is drawn through the port. Make sure the EGR valve pintle and base passages are clear as well. Install the valve.
BNaylor
08-21-2007, 12:52 AM
Or is this not the problem?
Not all EGR flow problems is a bad EGR valve, therefore, it may not be a bad EGR valve. On the SII 3800 Vin "K" engine an EGR low flow and failure of the test can be caused by a defective PCV valve or seal. Mainly a deteriorated or missing o-ring seal. If you had any work done on the PCV valve like replacement check for a missing or omitted o-ring seal. Without the o-ring DTC P0401 can set. :grinyes:
The PCV valve is located under the MAP sensor at the right hand side (passenger) of the Upper Intake Manifold (Plenum).
Also, an EGR low flow can be caused by the infamous UIM Plenum problem related to the EGR stovepipe and/or bad UIM gasket.
Not all EGR flow problems is a bad EGR valve, therefore, it may not be a bad EGR valve. On the SII 3800 Vin "K" engine an EGR low flow and failure of the test can be caused by a defective PCV valve or seal. Mainly a deteriorated or missing o-ring seal. If you had any work done on the PCV valve like replacement check for a missing or omitted o-ring seal. Without the o-ring DTC P0401 can set. :grinyes:
The PCV valve is located under the MAP sensor at the right hand side (passenger) of the Upper Intake Manifold (Plenum).
Also, an EGR low flow can be caused by the infamous UIM Plenum problem related to the EGR stovepipe and/or bad UIM gasket.
Automotive Network, Inc., Copyright ©2026