P0401 Ford - expedition

Question

My mechanic has changed and done
EGR passage clogged
- Faulty EGR Vacuum Modulator Valve
- Faulty EGR Valve
- Faulty EGR solenoid valve
- EGR solenoid valve harness is open or shorted
- EGR solenoid valve circuit poor electrical connection
- Dead (Weak) battery
- Faulty EGR temperature sensor and circuit
- Exhaust gas leaks
The light has not turned off, we even changed the computer
What else cold it be? Please help greatly appreciate it.

Answer 1

P0401 EGR gas recirculation flow insufficient detected

 When you are dealing with a low to no flow you would need to check for vacuum at the EGR solenoid. , proper vacuum routing for the EGR system and proper back pressure hose at the EGR backpressure transducer

 Make sure the hose is correct here, there are 2 different sizes for the back pressure hose.

 From here this EGR on one side should have vacuum from the intake , you can remove the EGR cap to check that the EGR passage is clear

 

 Here a test for the EGR valve and a test to check if the EGR passage is clear.with the engine runnng and a finger is placed on the EGR solenoids vent . it should cause the EGR valve to open and the engine should either stumble or stall out.

 By doing this on this Ford, it was determined that the passage of the EGR was still plugged, and the removal of the throttle body was the only way to slear out the passage for the EGR passage.