P0406 on the 6.0L Power Stroke is an exhaust gas recirculation (EGR) position sensor A circuit high fault. The 6.0L uses an EGR valve with a position sensor so the PCM can confirm the valve is where it was commanded. P0406 sets when the PCM reads the EGR position sensor signal too high, which means it cannot trust the feedback that verifies EGR operation and may limit power or set companion codes.
The 6.0L EGR system runs in a heavily sooted environment, and both the valve and its position sensor take abuse over the miles. P0406 is a sensor circuit fault, so the diagnosis centers on the sensor, wiring, and connector, though soot that binds the valve or fouls the sensor can also contribute. Working through the electrical path first keeps you from replacing an EGR valve when the real fault is a wire or a ground.
What P0406 means
The EGR position sensor reports valve position back to the PCM as a voltage. P0406 sets when that voltage reads too high, indicating a signal shorted to reference or voltage, a lost ground allowing the signal to float high, or a failed sensor. The PCM loses its ability to confirm the commanded EGR position and flags the fault.
Common causes
- Signal wire shorted to reference or voltage
- Open or high-resistance sensor ground
- Corroded or loose EGR connector
- Failed EGR position sensor
- Soot fouling affecting the sensor or valve movement
Symptoms
- Check engine light with P0406 stored
- Reduced power or a derate in some cases
- Rough idle or hesitation
- Possible increased emissions
- Companion EGR valve or flow codes
How to diagnose it
With a scan tool, watch the EGR position feedback while commanding the valve; a reading pinned high that does not track confirms the fault. Inspect the EGR connector and wiring for corrosion, chafing, and a secure fit. Back-probe the connector and confirm a clean ground and the correct reference, since a lost ground drives the signal high. Check the signal wire for a short to reference or voltage. Evaluate whether soot is binding the valve or fouling the sensor.
How to fix it
Restore a poor ground and repair any wiring shorted to reference or voltage first, then clean or replace a corroded connector, which fixes many P0406 cases. If the wiring checks good but the position sensor still reads high, replace the EGR valve assembly, since the sensor is integrated on the 6.0L. Clean soot binding if present. After the repair, clear the code, command the valve through its range, and confirm the position feedback tracks, then road test. For EGR valves and related parts for your 6.0L, contact sales@coredieselparts.com.
Frequently asked questions
Can I clean the EGR valve to fix P0406?
Cleaning helps if soot is binding the valve or fouling the sensor, but P0406 is primarily an electrical high reading. Check the ground and wiring first, then clean or replace as needed.
Is P0406 the sensor or the wiring?
Both are possible. A lost ground or a short to voltage reads high just like a failed sensor. Confirm the ground and reference before replacing the valve assembly.
Will P0406 cause a derate?
It can. Loss of EGR position feedback affects emissions and drivability, and the PCM may limit power until the fault is repaired.
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