What this code means
P0404 means the PCM may be seeing the commanded EGR valve position and the actual position feedback not agree the way it expects.
What the vehicle may do
- The MIL may illuminate.
- The vehicle may run normally, or it can have an EGR-related drivability complaint.
Possible fault areas
- A possible 5-volt supply circuit issue.
- Possible connector or terminal problems at the EGR valve circuit.
- A possible sticking or carboned-up EGR valve.
- Possible excessive EGR motor winding temperature.
- Possible fuel or air handling issues that may contribute to soot or carbon buildup.
Diagnostic path
Open: what P0404 is telling you
On this Ram, P0404 is an EGR position sensor performance fault. In plain terms, the PCM is commanding the cooled EGR valve and watching whether the position feedback follows the desired position. The driver may only notice the MIL, and the truck can also have an EGR-related drivability complaint. Keep the fault areas broad at the start: possible 5-volt supply trouble, connector or terminal problems, a sticking or carboned-up EGR valve, excessive EGR winding temperature, or engine fuel and air handling issues that may be loading the valve with soot. Before going deep, start with the basic system checks and follow a structured diagnostic approach.
System logic before testing
The EGR valve assembly is an electric DC motor and gearbox driving a linear output shaft. The PCM runs it with an H-bridge and PWM control so it can open the valve, hold position, and protect the motor from overheating. The return spring brings the valve closed as a fail-safe. The full output shaft travel is approximately 5.0 mm, and over that travel the position sensor reading changes approximately 3.9 volts. During normal operation, the sensor signal runs between approximately 0.5 volts closed and 4.3 volts open. Current is highest during opening, with a typical peak of approximately 6.0 amps, then the duty cycle is reduced to about a typical average of approximately 0.5 amps while holding the valve open. When you watch this system work, motor current and position sensor voltage together tell the story.
Start with bulletins and software
First, check for any applicable service bulletins or PCM software updates tied to this fault. If one applies, handle that repair or flash first, then verify the repair and confirm the code stays gone. If there is nothing applicable, move on without assuming the valve is bad.
Record data, clear codes, and see if P0404 returns
Next, use the scan tool to read codes in all ECUs, record them on the repair order, and save a vehicle scan report with the related recorded data. If other codes are present, understand what they mean first, but keep this path focused on P0404. Clear the codes, turn the ignition off for a minimum of 10.0 seconds, then turn the ignition back on. Now reproduce the operating conditions that set the fault. The monitor is looking for the engine running for more than one minute, and throttle input showing an open throttle condition for more than approximately 2.0 seconds. After that, read the codes again. If P0404 returns, go straight to the 5-volt supply check. If it does not return, treat it like an intermittent or history-based EGR performance issue and check the recent repair history.
If the code did not return, use the repair history
If P0404 does not reset during the retest, check whether the vehicle had an EGR valve performance fault within the past 90 days. If it was in for this and the valve was cleaned last time, make sure the connector is fully seated and inspect the terminals for being pushed out, corroded, or spread. If that connector inspection is good, the next supported move is replacing the EGR valve assembly, then running the scan-tool routine that resets the EGR valve zero-learn position. If the valve was replaced last time, do the same connector and terminal checks. If those are good, clean the valve by running Mopar Combustion Chamber cleaner through the engine, run the zero-learn reset routine, road test it, and confirm the fault does not return. If it stays gone, check for fuel or air handling issues that can cause excessive soot or carbon buildup. If there was no recent EGR performance history, still verify the connector and terminals, clean the valve with the Mopar cleaner through the engine, run the zero-learn reset routine, road test, and verify the code does not return. Any time the valve is replaced or cleaned, that routine is not optional. If the zero-learn position is not reset, the vehicle can set a false failure code.
If P0404 returned, check the 5-volt supply at the EGR sensor connector
When P0404 comes right back, move to the EGR position sensor 5-volt supply. Turn the ignition off, disconnect the EGR sensor harness connector, and leave the ECU harness connector connected for this check. Turn the ignition on, set the DVOM to DC volts, put the negative lead on a known good ground, and measure the 5-volt supply at the EGR sensor harness connector. Normal operating voltage should be between 4.8 and 5.2 volts. Do not probe the PCM harness connectors. If you need to test at a PCM connector, use the GPEC Diagnostic Adapter 10436, and remember that adapter can add up to 1.5 Ohms of resistance to the circuit. If the 5-volt supply is not correct, repair the F855 5-volt supply circuit for an open or a short to ground, then verify the repair and confirm the code stays gone. If the supply voltage is correct, continue to the valve inspection.
Inspect the valve for carbon or soot
With the 5-volt supply passing, turn the ignition off, remove the EGR valve assembly, and inspect the valve stem, disc, and passages for damage or excessive carbon and soot. If there is excessive buildup, clean and reinstall the EGR valve assembly. Then run the zero-learn reset routine, road test the vehicle, and verify P0404 does not return. If the valve does not show excessive carbon or soot buildup, replace the EGR valve assembly, run the zero-learn reset routine, and verify the repair. Keep the verification separate from the testing: after the repair action, confirm the monitor can run and the code stays gone.
Closing takeaway
The clean path on P0404 is simple: prove whether the fault returns, use recent EGR history when it does not, check the 5-volt supply when it does, and do not skip the zero-learn reset after cleaning or replacing the valve. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0404 is best handled by confirming whether the fault returns, separating intermittent history from an active fault, checking the sensor supply circuit, and verifying the EGR valve condition.
For more guided automotive diagnostics, visit STEP Diagnostics.
