P0405 — Exhaust Gas Recirculation Sensor A Circuit Low — 6.4 Power Stroke

Diagnostic reference for the 6.4L Power Stroke (2008-2010) EGR position sensor circuit low code.

Updated October 15, 2026

What it means

The EGR valve position sensor signal voltage is below its valid range. On the 6.4L this is an EGR/EGR position sensor circuit issue. The platform has an EGR valve plus an EGR cooler; flow/position codes include P0401, P0402, P0404, P042E and P2457 (EGR cooling system performance).¹

Most likely causes

1. EGR valve position sensor internal failure or biased low output — Sensor signal stays below valid range even with good wiring and a free-moving valve.¹
2. EGR valve connector or harness chafed/shorted to ground — Wiring damage near the hot EGR area pulls the position signal low.¹
3. Sooted or sticking EGR valve causing abnormal position feedback — Carbon buildup can make the valve stick and the position sensor read out of range; this often accompanies P0405 on the 6.4L.¹
4. PCM reference voltage or ground fault affecting the EGR position sensor circuit — A low 5 V reference or poor sensor ground can make the position signal read low.¹

How to diagnose

1. Verify freeze-frame conditions and confirm P0405 is present with no other EGR-related codes masking the fault.
2. Inspect the EGR valve electrical connector for heat damage, corrosion, and proper seating; check the harness for chafing near the EGR valve and cooler.
3. Check the EGR position sensor signal voltage key-on/engine-off and compare to the expected range; a persistently low voltage supports a circuit low condition.
4. Command EGR valve movement with a scan tool while monitoring EGR position PID; look for a stuck or non-responsive position reading consistent with soot/sticking.
5. Inspect the EGR valve pintle and bore for heavy carbon/soot accumulation that could cause sticking and abnormal position feedback.
6. Check the sensor reference voltage and ground circuits at the EGR connector for correct values and continuity to the PCM.
7. If the wiring and reference are good but the signal remains low, evaluate the EGR valve position sensor as faulty; if the valve is heavily sooted/sticking, address the mechanical condition before condemning the sensor.

Common mistake to avoid

Replacing the EGR valve without testing it. If the valve still moves freely, a carbon cleaning often fixes the flow code; and if it opens on command but the code stays, the blockage is in the passages or cooler, not the valve. Source: FleetRabbit — EGR valve problems and repair.

Parts and tools you may need

• Digital multimeter
• Scan tool with live data and bi-directional EGR control
• Inspection light and mirror
• Dielectric grease
• Basic hand tools for connector access

Tools you’ll need

• OBD-II scan tool — Reads P0405 and monitors EGR position PID while commanding valve movement to confirm a low signal or stuck valve.
• digital multimeter — Measures key-on EGR position sensor signal, reference voltage, and ground to identify a short-to-ground or biased-low circuit.
• inspection mirror — Lets you view the EGR valve pintle and bore for heavy carbon/soot buildup that can cause sticking and abnormal position feedback.
• borescope — Provides a close look inside the EGR valve bore and cooler passages for soot accumulation without full disassembly.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If high-pressure fuel injection service is required, or if the EGR system requires removal in a high-temperature environment, have a qualified diesel technician perform the work. Do not attempt step-by-step repair of safety-critical systems. If the vehicle shows sudden power loss, white smoke, or fuel in oil, seek immediate professional diagnosis.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources