Had P0402 now P0401 1999 ranger
 

1999 Ford Ranger 3.0 Flex 4x4

Diagnostic Trouble Code and Definition

P0402 - Exhaust Gas Recirculation Flow Excessive Detected

P0402 is the DTC that caused this Freeze Frame Data to be stored

Fuel System 1 Status: Closed Loop Control using Oxygen Sensor - Normal
Calculated Load: 42.4%
Coolant Temperature: 89 Deg C 192.2 Deg F
Short Term Fuel Trim Bank 1: 2.34% Rich(+)
Long Term Fuel Trim Bank 1: 4.69% Lean(-)
Short Term Fuel Trim Bank 2: 1.56% Rich(+)
Long Term Fuel Trim Bank 2: 2.34% Lean(-)
Engine Speed: 859.25 Rpm
Vehicle Speed 0 Kmh 0 Mph
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and heres some live data i recorded with it running with P0402

Absolute Throttle Position: 16.1%
Engine Speed: 909.25 Rpm
Vehical Speed: 0 Kmh 0 Mph
Calculated Load: 33.7%
Ignition Timing Advance Cyl#1: 12 Degrees Advance(+)
Fuel System 1 Status: Closed Loop Control using Oxygen Sensor-Normal
Mass Air Flow: 5.59 g/s 0.7 lb/min
Short Term Fuel Trim Bank 1: 2.34% Rich(+)
Short Term Fuel Trim Bank 2: 2.34% Rich(+)
Long Term Fuel Trim Bank 1: 0.78% Rich(+)
Long Term Fuel Trim Bank 2: 2.34% Rich(+)
Coolant Temperature: 89 Deg C 192.2 Deg F
Intake Air Temperature: 44 Deg C 111.2 Deg F
Bank 1 Sensor 1: 0.710V
Short Term Fuel Trim: 0.78% Lean(-)
Bank 1 Sensor 2: 0.660V
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Here is the code that came after clearing the P0402 DTC, the P0402 is
pending now.

P0401 - Insufficient Exhaust Gas Recirculation flow

P0401 is the DTC that caused this Freeze Frame Data to be stored

Fuel System 1 Status: Closed Loop Control using Oxygen Sensor - Normal
Calculated Load: 58.4%
Coolant Temperature: 89 Deg C 192.2 Deg F
Short Term Fuel Trim Bank 1: 3.91% Lean(-)
Long Term Fuel Trim Bank 1: 0.78% Lean(-)
Short Term Fuel Trim Bank 2: 4.69% Lean(-)
Long Term Fuel Trim Bank 2: 0.78% Rich(+)
Engine Speed: 2105.25 Rpm
Vehicle Speed 81 Kmh 50 Mph
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Im not sure if anyone can tell my issue from these data readings but its better then nothing. So far i first started with DTC codes P0401,P0171,P0174 replaced the DPFE cleared code but it came back so i returned the DPFE and got a new EGR cleared code and back again. It could be that both the DPFE and egr were bad but i have not replaced it again yet(DPFE very common issue on rangers im told). Then my ranger started to stall randomly and i found in the end the issue was a bad PCM relay. After replacing it i only had a P0402 DTC and after clearing that i got the P0401 DTC again. My next step is checking DPFE volts somehow not sure yet, checking for leaks, running seafoam and if all fail taking apart and cleaning everything... trying to avoid that if possible. If anyone has helpful tips please let me know.

hey i have some of the similar problems going. i recently took apart the egr system and cleaned the valve, took the throttle body off and it was completely nasty with buildup, cleaned that. my truck is randomly stalling still and i now have a dpfe code and went from p0401 to p0402. have you made any progress? i would suggest removing the throttle body and cleaning it.