Code P0405: Exhaust Gas Recirculation Sensor A Circuit Low

Vehicles keep nitrogen oxide (NOx) emission levels under control using exhaust gas recirculation (EGR) systems. When the sensor that monitors the position of the EGR valve sends signals with lower voltage levels than normal, an OBD scan tool may register the code P0405.

What Does the P0405 Code Mean?

Diagnostic trouble code (DTC) P0405 stands for “Exhaust Gas Recirculation Sensor A Circuit Low.” It denotes that the readings coming from the EGR valve position sensor show lower voltage levels than normal.

As its name implies, the EGR position sensor detects the position of the EGR valve. The powertrain control module (PCM) uses the sensor signal to monitor and adjust EGR valve operation. If the signal from the sensor appears strangely low, the PCM may set a P0405 code.

For more information, you may read our technical discussion about the EGR system. If you’re planning a DIY fix, you may also want to read about the EGR sensor and Delta Pressure Feedback EGR (DPFE).

Continue reading to learn the possible causes of code P0405.

Note: Code P0316 is a generic code specified by the Society of Automotive Engineers (SAE). Depending on the car manufacturer, the code’s definition may change.

What are the Possible Causes of the P0405 Code?

You may get taken aback by the number of issues that can get the PCM to set an engine code P0405. Likely causes for this DTC include:

• Faulty EGR valve position sensor or DPFE
• Bad EGR valve
• Circuit issues, such as damaged or chafing wires or poor connections
• An issue with the PCM, such as software in need of an update

What are the Common Symptoms of the P0405 Code?

When the EGR valve position sensor stops working correctly, it can disrupt the vehicle’s drivability. Warning signs of a code P0405 include:

• Illuminated check engine light
• Failed emission test due to increased NOx emissions
• Decreased engine performance
• Engine pinging
• Poor fuel economy
• Engine stalling

Some vehicles won’t show any obvious signs that their EGR valve position sensor has stopped working properly. If your scanner shows a P0405 code, bring your ride to the shop for diagnosis and repair.

How to Diagnose the P0405 Code

The variations between EGR systems can make a code P0405 a challenge to diagnose and fix. You can learn what the troubleshooting process might involve by watching the videos below:

How to Fix the P0405 Code

Fixing the P0405 code involves pinpointing its exact cause and resolving it with consideration to your vehicle’s make and model. Most DIYers tend to overlook the latter, mistakenly assuming that what works for one works for all.

If you are not confident with your automotive know-how and repair skills, it may be best to let your mechanic fix the issue. Otherwise, feel free to tackle the engine code. Once you’ve identified what triggered it, figure out the best way to fix it using online auto repair resources and guides. Better yet, secure an ALLDATA single-vehicle subscription to get access to comprehensive factory repair information.

Lastly, double-check your owner’s manual before implementing any repair process. Make sure the solution is not only the right fix for what triggered the engine code but also appropriate for your vehicle.

EGR Sensors and DPFE

Early fuel injected Fords had a vacuum solenoid and a three wire linear EGR Valve Position (EVP) sensor that measured diaphragm movement. But monitoring pintle position doesn’t prove EGR gas is flowing into the intake.

GM vehicles (pre-OBD2) will watch O2 sensor activity while the ECM is commanding EGR flow, because O2 sensor readings will drift slightly rich when EGR is flowing due to the displacement of oxygen by the inert exhaust gas entering the intake.

Pre-OBD2 Ford engineers developed a different feedback system, with a 3-wire pressure sensor that first appeared on Lincoln Town Cars in 1991. That sensor has two silicone hoses connected to the EGR feed pipe with an orifice between the two hoses. Ford dubbed this the “DPFE” sensor, for Delta Pressure Feedback EGR. That system remained on OBD2-era Fords equipped with EGR.

Pre-OBD2 Ford engineers developed a different feedback system, with a 3 wire pressure sensor that first appeared on Lincoln Town Cars in 1991. That sensor has two silicone hoses connected to the EGR feed pipe with an orifice between the two hoses. Ford dubbed this the “DPFE” sensor, for Delta Pressure Feedback EGR. That system remained on OBD2 era Fords equipped with EGR.

–Richard McCuistian, ASE Certified Master Automobile Technician

On the Ford, when EGR is flowing, the pressure will rise in the hose connected below the orifice in the EGR feed pipe and the pressure will drop in the hose connected above it, thus the sensor can determine if EGR is flowing and how much. This is a three-wire sensor (5V, Signal Return ground, and Signal). The signal wire on metal DPFE sensors rests at about 0.6 volts and on the plastic ones at about 1.0 volts.

If this sensor voltage reads lower than the expected window, the P0405 code is set.

Where to Get Replacement Parts for Your Vehicle

If your scan tool reads a P0405 code, you don’t have to worry. CarParts.com has all the parts you need to get your vehicle back on the road again.

We have a wide selection of replacement parts like EGR valves and EGR valve position sensors sold at unbeatable prices. Just visit our website and use our vehicle selector tool to narrow down your search to the replacement parts that are compatible with your specific year, make, and model.

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Products Mentioned in this Guide

EGR Valve EGR Valve Position Sensor