P0404: P0404 Diagnostic Guide

What this code means

P0404 may mean the PCM sees the electric EGR valve position not matching the commanded position.

What the vehicle may do

The vehicle may turn on the check engine light.
The vehicle can have possible driveability complaints depending on when the EGR fault occurs.
The concern may be intermittent if the harness or connector connection changes with movement.

Possible fault areas

Possible electric EGR valve circuitry concern.
Possible EEGR connector or terminal condition.
Possible EGR valve concern.
Possible related MAP or MAF input concern.
Possible PCM-side concern.

Diagnostic path

Set up the P0404 diagnosis

On this 2.7 EcoBoost F-150, P0404 is an electric EGR code. In plain terms, the PCM may be seeing the EGR valve in a position that does not match what it commanded. The truck may just have a check engine light, or it can have driveability complaints depending on when the EGR fault shows up. The broad possible fault areas are the EGR valve and its circuits, related airflow or pressure inputs, and, less often, the controller side. Start with the basic system checks, then keep the diagnosis structured so you do not condemn the EGR assembly before the wiring and connector checks are done.

Confirm the code path

With the ignition on, check which faults are actually present. For P0404, follow the electric EGR diagnostic path into the connector and circuit checks. If other EGR-related codes are present, do not read the whole list out loud or shotgun the same test for all of them. Check what those codes mean first, because some of them branch to a different part of the diagnostic routine. For this episode, we are staying focused on P0404.

Inspect the EEGR connector first

Next, check the EEGR connector. Make sure the terminals are clean, seated correctly, and not creating an intermittent connection. If the code is intermittent, wiggle the harness and connector while you are taking measurements. If the connector is not clean or seated correctly, repair that issue as necessary, clear the PCM DTCs, and repeat the self-test. If the connector checks good on this 2.7 EcoBoost, continue with the electrical checks in order.

Check the open-circuit voltage branch

If the diagnostic path calls for the EGR circuit open check with the ignition on, disconnect the EEGR assembly connector and make the voltage decision before moving on. The question is whether the voltage is greater than 10.5 V. If it is greater than 10.5 V, continue to the resistance open check. If it is not, repair the open circuit, clear the PCM DTCs, and repeat the self-test.

Check the EGR control circuits for opens

Turn the ignition off, disconnect the EEGR assembly connector, and disconnect the PCM connector. On the 2.7 EcoBoost, check resistance between C1682 Pin 4 and C1232E Pin 2, then between C1682 Pin 5 and C1232E Pin 23. The resistance needs to be less than 5 Ω. If it is not less than 5 Ω, repair the open circuit, clear the PCM DTCs, and repeat the self-test. If both legs are less than 5 Ω, continue with the short checks.

Check for shorts on the EGR circuits

Now keep the connectors disconnected and work through the short checks in order. First, check the EGR circuits for a short to ground at C1682 Pin 4 and C1682 Pin 5. Each check should show greater than 10000 Ω. If not, repair the short circuit, clear the PCM DTCs, and repeat the self-test. Next, check for a short between the two EGR circuits by measuring between C1682 Pin 4 and C1682 Pin 5. That also 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 turn the ignition on and check for voltage at C1682 Pin 4 and C1682 Pin 5. If any voltage is present, repair the short circuit, clear the PCM DTCs, and repeat the self-test. If no voltage is present, go to the EGR coil check.

Check the EGR coil resistance

With the ignition off, measure the EGR coil resistance on the component side between C1682 Pin 4 and C1682 Pin 5. The resistance should be between 1 - 900 ohms. If the resistance 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 and verify whether the concern is still present.

Handle the MAP and running-test branch

There is also a MAP sensor operation branch in this electric EGR routine. With the ignition on, monitor the PCM MAP PID in kPa, record the value, start the engine, and record it again. The expected decision is that the MAP PID value is higher than 69 kPa (10 psi) with the ignition ON, engine OFF, and lower than 69 kPa (10 psi) with the ignition ON, engine RUNNING. If it meets that pattern, the concern is not present at this time, so make sure the MAP sensor is correctly seated and the vacuum source is not restricted, then clear the PCM DTCs and repeat the self-test. If it does not meet that pattern, carry out the key on, engine running self-test. If the related EGR flow fault comes back, leave this P0404 path and continue with the appropriate flow-diagnosis path. If it does not come back, continue with symptom-based direction instead of guessing.

Check the EGR position feedback circuit branch

If the diagnosis branches into the EGR position feedback and reference side, start with VREF and signal return. With the ignition off, disconnect the EEGR assembly connector, then turn the ignition on. On the 2.7 EcoBoost, measure voltage between C1682 Pin 3 and C1682 Pin 1. The voltage should be between 4.5 V - 5.5 V. If it is not in that range, move into the reference-voltage and signal-return diagnosis before continuing. If it is in range, turn the ignition off, disconnect the PCM connector, and check the EGRVP circuit between C1682 Pin 2 and C175E Pin 47. That resistance needs to be less than 5 Ω. If not, repair the open circuit, clear the PCM DTCs, and repeat the self-test. Then check the EGRVP circuit for a short to ground at C1682 Pin 2. The resistance should be greater than 10000 Ω. If it is not, repair the short circuit, clear the PCM DTCs, and repeat the self-test. Finally, turn the ignition on and check C1682 Pin 2 for voltage. If any voltage is present, repair the short circuit, clear the PCM DTCs, and repeat the self-test. If no voltage is present, go back to the final operation check.

Verify the concern after reconnecting

Reconnect the EEGR assembly connector and the PCM connector, then verify whether the concern is still present. If the concern is still present after the circuit checks have passed, 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.

Closing takeaway

The key on P0404 is to prove the command and feedback path before making the parts call: connector condition, opens, shorts to ground, shorts between circuits, shorts to voltage, EGR coil resistance, and then final verification. If the wiring checks pass and the concern remains, the test path points to the EGR assembly. For more diagnostic training, visit stepdiagnostics.com.