P0401: EGR flow insufficient detected

What this code means

P0401 means the PCM may be detecting less exhaust gas recirculation flow than expected.

What the vehicle may do

The vehicle may have a check engine light.
Driveability can often be normal, but some vehicles may show EGR-related running complaints.

Possible fault areas

Possible DPFE sensor, hose, or orifice tube concerns.
Possible wiring, connector, or circuit concerns.
Possible carbon buildup, restriction, or water intrusion.
Possible electric EGR assembly concerns.

Diagnostic path

Opening context for P0401

On this 2015 to 2025 Ford F-150 with the 2.7 EcoBoost, P0401 means the PCM may be seeing less EGR flow than it expects. The truck may only have a check engine light, but depending on the condition it can also have driveability complaints tied to EGR flow. Broadly, the possible fault areas are the DPFE sensor and its hoses, the EGR orifice tube, wiring and connector issues, carbon or water intrusion, and the electric EGR assembly. Start with the basic system checks, and if other codes are present, check what they mean first. Circuit faults get handled before range or performance faults, so you do not chase a flow code with a bad signal circuit still on the truck.

Check the DPFE reference and return circuits first

With P0401 present, begin at the DPFE side of the system. Key off, disconnect the Differential Pressure Feedback EGR sensor, then key on and check the reference and signal return at connector C1068, Pin 3 to Pin 2. On the 2.7 EcoBoost, you are looking for 4.5 V - 5.5 V. If that voltage is not there, the path leaves this EGR flow routine and the reference voltage concern has to be handled before continuing. If the voltage is correct, move on to the DPFE signal circuit checks.

Prove the DPFE signal circuit is intact

Next, key off and disconnect the PCM connector. Check the DPFE circuit between C1068 Pin 1 and C1232E Pin 79. Resistance needs to be less than 5 Ω. If it is not, repair the open circuit, clear the PCM DTCs, and repeat the self-test. If the circuit is intact, continue by checking that same DPFE circuit for a short to ground. The resistance needs to be greater than 10000 Ω. If it is not, repair the short circuit, clear the PCM DTCs, and repeat the self-test.

Check for voltage on the DPFE signal and stress the harness

Now check the DPFE circuit for a short to voltage. Key on, measure at C1068 Pin 1 as directed by the circuit test. If any voltage is present, repair the short circuit, clear the PCM DTCs, and repeat the self-test. If there is no voltage present, reconnect the DPFE sensor and PCM connectors, key on, and monitor DPFE_PRES in kPa and DPFE_V in volts. Wiggle, shake, and bend small sections of the harness while working from the sensor back toward the PCM. If the readings change or the concern shows up, repair as necessary, clear the PCM DTCs, and repeat the self-test. If the readings stay stable, continue into the EGR pressure hose and orifice inspection.

Inspect the DPFE hoses, orifice tube, and pickup areas

At this point, inspect the upstream and downstream DPFE pressure hose routing. Look for leaks, restrictions, water intrusion, and carbon buildup. Also inspect the DPFE sensor and orifice tube assembly for restriction or damage at the pickup tubes, along with water intrusion and carbon buildup. If water intrusion is the concern, install a new Differential Pressure Feedback EGR sensor and clean the hoses and orifice tube. For other concerns found here, repair as necessary. After the repair, clear the PCM DTCs and repeat the self-test. If the inspection is clean, go to the DPFE sensor output test.

Test DPFE sensor response with vacuum

Before testing the sensor output, make sure a previous repair did not swap the DPFE hoses onto the wrong ports. Reconnect the pressure hoses to the DPFE sensor. With the key on, monitor DPFE_PRES in kPa and DPFE_V in volts. Record the DPFE PID value with the engine off, then start the engine and record it running. The difference between those two values must be less than 0.075 volts (0 kPa). Then, with the key on, disconnect the pressure hose closest to the electrical connector and connect a vacuum pump to that sensor port. Apply 27 - 30 kPa (8 - 9 in-Hg) vacuum, hold it for 10 seconds, and quickly release it. On the 2.7 EcoBoost, with key on and no vacuum applied, the DPFE PID value must be between 1.8 and 2.2 volts (0 kPa ). With vacuum applied, it must increase to greater than 4 volts (14.7 kPa ). When vacuum is released, it must drop back to between 1.8 and 2.2 volts (0 kPa ) in less than 5 seconds. If the DPFE PID shows a sensor concern, install a new Differential Pressure Feedback EGR sensor, clear the PCM DTCs, and repeat the self-test. If the DPFE sensor passes and P0401 is still the code path, continue to the electric EGR side of the diagnosis.

Move to the electric EGR connector and circuits

On the electric EGR side, confirm the code path and then check the EEGR connector. If this is intermittent, wiggle the harness and connectors while taking measurements. Make sure the connector contacts are clean and correctly seated. If they are not, repair as necessary, clear the PCM DTCs, and repeat the self-test. If the connector is good, key off, disconnect the EEGR assembly connector and the PCM connector, then check the EGR circuits for opens. On the 2.7 EcoBoost, measure between C1682 Pin 4 and C1232E Pin 2, and between C1682 Pin 5 and C1232E Pin 23. Resistance must be less than 5 Ω. If it is not, repair the open circuit, clear the PCM DTCs, and repeat the self-test.

Check the EGR circuits for shorts

If the EGR circuits are not open, check them for a short to ground. Resistance needs to be greater than 10000 Ω. If it is not, repair the short circuit, clear the PCM DTCs, and repeat the self-test. Then check for a short between the EGR circuits themselves, measuring between C1682 Pin 4 and C1682 Pin 5. Again, resistance needs to be greater than 10000 Ω. If it is not, repair the short circuit, clear the PCM DTCs, and repeat the self-test. Next, key on and check the EGR circuits for a short to voltage. If any voltage is present, repair the short circuit, clear the PCM DTCs, and repeat the self-test. If no voltage is present, continue to the EGR coil resistance check. If a measurement reference point is not clear during these short checks, pause, recheck the earlier diagnostic path, and avoid guessing.

Check the EGR coils and confirm the concern

Key off and measure the EGR coil resistance on the component side between C1682 Pin 4 and C1682 Pin 5. The resistance must be between 1 - 900 ohms. If it is outside that range, install a new Electric Exhaust Gas Recirculation assembly, clear the PCM DTCs, and repeat the self-test. If the coil resistance is in range, reconnect the EEGR assembly connector and PCM connector, then verify whether the concern is still present. If the concern is still present, install a new Electric Exhaust Gas Recirculation assembly, clear the PCM DTCs, and repeat the self-test. If the concern is no longer present, the system is operating correctly at this time, and the issue may have been caused by a loose or corroded connector.

Wrap-up and verification

Keep the verification separate from the testing. After any wiring repair, sensor repair, hose or orifice cleaning, or component replacement that is supported by the test result, clear the PCM DTCs and repeat the self-test. The takeaway for P0401 is simple: prove the DPFE signal and hoses first, prove the sensor response next, and only then move into the electric EGR circuit and coil checks. For more diagnostic training, visit stepdiagnostics.com.