Exhaust Gas Recirculation Sensor A Circuit High
The P0406 code means the vehicle's onboard diagnostic system has detected: Exhaust Gas Recirculation Sensor A Circuit High. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $100 - $400 (parts and labor)
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Common Symptoms
- Check Engine Light illuminated
- Rough or unstable idle
- Engine stalling
- Reduced power and hesitation
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Faulty EGR position sensor reading high Very High
- Open ground wire to EGR sensor High
- Short to 5V reference in EGR sensor signal wire Moderate
- ECM internal pull-up fault on EGR circuit Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0406 on specific vehicles — tap your vehicle for the fix and the exact part:
2004-2014 Ford F-150/Expedition 4.6L/5.4L easy DIY
P0406 means the EGR position sensor is reading higher than expected. On Ford trucks, the DPFE sensor is the most common failure. The updated Motorcraft has an improved circuit design. Also check for a clogged EGR tube -- carbon restriction causes backpressure that falsely elevates the sensor reading. Clean or replace the EGR tube. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 20-30 min2010-2020 Chevrolet Silverado/Suburban 5.3L/6.2L moderate DIY
On GM V8 engines, P0406 can be caused by a shorted EGR position sensor or carbon preventing the valve from fully closing. Remove the EGR valve and inspect the pintle seat for carbon buildup. If the valve does not close fully, the sensor reads high. Clean with carb cleaner. If the sensor reading stays high with the valve removed, the sensor/valve is faulty.
Labor: 30-45 min2006-2016 Ford Escape/Fusion 2.5L/3.0L easy DIY
The DPFE sensor on Ford cars is the same design as the trucks and fails just as often. The sensor misreads exhaust backpressure as high EGR flow. Replace with an OE-quality Motorcraft unit. While you are in there, pull the EGR vacuum hose and check for a stuck EGR vacuum regulator solenoid. A stuck-open solenoid also causes a high EGR reading. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 20-30 minFrequently Asked Questions
Can I drive with code P0406?
You can drive short distances. The ECM sees the EGR valve as fully open and may command it closed, or it may disable the EGR system entirely. This can cause rough idle and increased emissions.
What is the difference between P0405 and P0406?
P0405 indicates the EGR sensor voltage is below the expected range (too low), while P0406 indicates it is above the expected range (too high). Both point to the EGR position sensor or its circuit.
What causes the EGR sensor to read high?
A failed sensor, an open ground connection that lets the signal float high, or a signal wire shorted to the 5V reference are the most common causes of a high reading.
What actually makes the computer set an EGR code?
The OBD II regulation requires the system to flag EGR when flow deviates from the manufacturer's specified rate — in either direction, too much or too little — by enough to push emissions past 1.5 times the FTP standards; and, where no EGR fault could do that, when there is no detectable EGR flow at all (Title 13 CCR 1968.2, section (e)(8.2)). Note that excess flow is a malfunction too, which is why an EGR code does not automatically mean a blocked passage. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Check EGR position sensor voltage -- readings above 4.5V with valve closed indicate a fault
-
Verify ground wire continuity from the sensor connector to the ECM
-
Disconnect the sensor and measure voltage on the signal wire -- it should drop with sensor removed
-
Check for chafed wiring where the signal wire may contact the 5V reference line
-
Replace the EGR position sensor or EGR valve assembly if wiring checks out
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
P0406 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Commonly Affected Vehicles
- 2001-2012 Ford Escape
- 2003-2015 Ford F-150
- 2002-2013 Chevrolet Trailblazer
- 2004-2014 GMC Envoy
- 2005-2016 Dodge Grand Caravan
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