P0401 obd2 code and how EGR system works


P0401 obd2 code refers to an egr flow malfunction which needs a complete vacuum inspection. This includes testing vacuum activated solenoids that operate the egr system.
Please review also our obd2 list of codes as shown below.

P0401     EGR Flow malfunction

egr system

This is what you can do when you see this code: check all the sensors, solenoids related to your egr (exhaust gas regulator valve). Make sure to check your basics like vacuum connections including its presence of vacuum at idle/high idle rpm to the egr valve. Included in the test is the wiring connections to the sensors, solenoids up to the ecm. You would probably need a good wiring diagram to see this which is available at ATS. Note: if further advance test is required, this would need a scan tool so the vacuum going to the egr valve could be monitored by manually commanding the vsv to open the vacuum flow to the egr valve.

Symptoms of code P0401:

This code can cause your engine to clutter (ping) during acceleration just like the pre-ignition knock. This is noticeable specially when pulling a load or climbing steep grades.

Testing EGR components:

The vacuum supply going to the egr valve can be monitored at idle and at high idle. There should be no change in engine rpm if the egr valve pintle valve is manually lifted up (this is the egr open position or use a hand held vacuum pump connected to egr vacuum port to lift the pintle rod). Always clean the egr vacuum passage for blockage to make sure the flow is continuous. This can be done by soaking the passage ways with a carb cleaner and blowing them with an air blower. If possible, use a coat hanger to clean hard to access egr passage holes. Finally, it is cheaper to change the DPF egr valve and than changing the egr valve later.




CODE     Meaning or Description

P0400     EGR Flow
P0401     EGR Flow
P0402     EGR Flow
P0403     EGR Flow cntl ckt
P0404     EGR Flow cntl ckt
P0405     EGR Flow Sensor ckt
P0406     EGR Flow Sensor ckt
P0407     EGR Flow Sensor ckt
P0408     EGR Flow Sensor ckt
P0409     EGR Flow Sensor ckt
P040A     EGR Flow Temp Sensor ckt
P040B     EGR Flow Temp Sensor ckt
P040C     EGR Flow Temp Sensor ckt
P040D     EGR Flow temp Sensor ckt
P040E     EGR Flow Temp Sensor ckt
P040F     EGR Flow Temp Sensor ckt
P0410     Engine Air Injection System
P0411     Engine Air Injection Flow
P0412     Engine Air Injection Valve ckt
P0413     Engine Air Injection Valve ckt
P0414     Engine Air Injection Valve ckt
P0415     Engine Air Injection Valve ckt
P0416     Engine Air Injection Valve ckt
P0417     Engine Air Injection Valve ckt
P0418     Engine Air Injection Cntl ckt
P0419     Engine Air Injection Cntl ckt
P041A     EGR Temp Sensor Ckt
P041B     EGR temp Sensor Ckt
P041C     EGR Temp Sensor Ckt
P041D     EGR temp Sensor Ckt
P041E     EGR Temp Sensor Ckt
P041F     Engine Air Injection Valve ckt
P0420     Catalytic converter (Bank 1)
P0421     Catalytic converter (Bank 1)
P0422     Catalytic converter (Bank 1)
P0423     Catalytic converter (Bank 1)
P0424     Catalytic converter temp (Bank 1)
P0425     Catalytic converter sensor (Bank 1)
P0426     Catalytic converter sensor (Bank 1)
P0427     Catalytic converter sensor (Bank 1)
P0428     Catalytic converter sensor (Bank 1)
P0429     Catalytic converter heater cntl (Bank 1)
P042A     Catalytic converter sensor (Bank 1)
P042B     Catalytic converter sensor (Bank 1)
P042C     Catalytic converter sensor (Bank 1)
P042D     Catalytic converter sensor (Bank 1)
P042E     EGR Cntl
P042F     EGR Cntl
P0430     Catalytic converter (Bank 2)
P0431     Catalytic converter (Bank 2)
P0432     Catalytic converter (Bank 2)
P0433     Catalytic converter (Bank 2)
P0434     Catalytic converter (Bank 2)
P0435     Catalytic converter temp (Bank 2)
P0436     Catalytic converter temp (Bank 2)
P0437     Catalytic converter temp (Bank 2)
P0438     Catalytic converter temp (Bank 2)


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