Exhaust Gas Recirculation Sensor B Circuit Low
The P0407 code means the vehicle's onboard diagnostic system has detected: Exhaust Gas Recirculation Sensor B Circuit Low. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $120 - $450 (parts and labor)
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Common Symptoms
- Check Engine Light illuminated
- Rough idle
- Poor engine performance
- Increased NOx emissions
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Faulty secondary EGR position sensor Very High
- Short to ground in EGR sensor B signal wire High
- Corroded or water-damaged sensor connector Moderate
- ECM input circuit fault for sensor B Low
Frequently Asked Questions
Can I drive with code P0407?
You can drive short distances. The secondary EGR sensor fault may cause the ECM to run the EGR system in a default mode, affecting idle quality and increasing emissions.
What is EGR Sensor B?
Some vehicles with dual EGR systems or redundant sensors use a B sensor for additional feedback. Sensor B is typically the secondary EGR position sensor used for monitoring or verification.
Is P0407 common?
P0407 is less common than P0405/P0406 because not all vehicles use a secondary EGR sensor. It is more frequently seen on diesel trucks and heavy-duty applications.
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
-
Identify which sensor is sensor B for your specific vehicle using service information
-
Check sensor B voltage on a scan tool -- voltage below 0.3V indicates a low circuit fault
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Inspect the sensor connector for moisture, corrosion, or bent pins
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Check the signal wire for short to ground with a multimeter
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Verify 5V reference voltage at the sensor B connector
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
P0407 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
- 2005-2016 Ford F-250 Super Duty
- 2006-2018 Dodge Ram 2500
- 2004-2015 Chevrolet Silverado 2500HD
- 2007-2017 GMC Sierra 2500HD
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