P0405 Code – Meaning, Causes, Symptoms (& How To Fix)

P0405 - Exhaust Gas Recirculation Sensor A Circuit Low

P0405 Code

The Check Engine Light is on the dash yet again and you are banging your head in frustration. Once you get out your code scanner, you find the P0405 code, but what does this mean? This particular trouble code points to issues with the exhaust gas recirculation (EGR) system. 

In this article, we review what causes this fault and we show you how to diagnose it. We also cover a few tips to keep in mind while you perform the repair. 

Code P0405 Definition

P0405 – Exhaust Gas Recirculation Sensor A Circuit Low

What Does the P0405 Code Mean?

Trouble code P0405 indicates that the readings coming out of the exhaust gas recirculation (EGR) valve position sensor are incorrect. With this code, the voltage levels coming from the sensor are lower than they should be. 

The EGR position sensor monitors the position of the EGR valve. The information is sent to the powertrain control module (PCM), where it monitors the EGR valve’s operation. If the signal coming from the sensor is low, the PCM is going to set the trouble code. 

P0405 Trouble Code Symptoms

In many cases, the only symptom of the P0405 trouble code is a Check Engine Light on the dashboard. However, there are instances when other troubles will be present. 

Here are a few you can look for:

Causes of the P0405 Code

There aren’t too many issues that can lead to the P0405 trouble code. Typically, the problem is with the EGR valve position sensor or the PCM. 

Here are a few possibilities:

How Serious is the P0405 Code?

Low – Most of the time, there are no symptoms other than the Check Engine Light and possibly a failed emissions test. However, you don’t want to leave the problem unchecked. 

If left unrepaired, the engine could begin running rougher and eventually lead to a stalling situation. It’s best to have it repaired immediately, especially since the emissions aren’t ideal for the environment. 

What Repairs Can Fix the P0405 Code?

There are several repairs that can fix the P0405 code, depending on what’s causing the problem. It’s important that you perform complete diagnostics first to ensure you know what’s wrong. Here are a few of the possible solutions.

  • Repair EGR position sensor wiring or connection.
  • Replace EGR position sensor
  • Replace differential pressure feedback electronic (DPFE) sensor
  • Check PCM connection/update software
  • Replace PCM

Common P0405 Diagnosis Mistakes

It’s common for people to replace parts when they aren’t defective. That’s why it’s important to check the connection and wiring harness to the EGR position sensor before you replace it. The problem could be a simple short or open circuit. 

You should also check all of the wirings. These simple issues should be checked before you replace the EGR position sensor. 

Recommended Tools for Diagnosis

How to Diagnose the P0405 Trouble Code

Here are some steps that professional mechanics will take to diagnose the P0405 trouble code.

  1. Use your scan tool to command the EGR valve on. If the valve responds, the problem may just be intermittent. This is common when the weather is cold and moisture becomes frozen. Once the vehicle warms up, the problem may no longer be present. Debris and carbon can also become stuck to the valve.
  2. If the valve doesn’t respond, disconnect the harness connector to the EGR. 
  3. Turn your key to the ON position, but keep the engine turned off.
  4. With your voltmeter, measure the reference wire going to the EGR valve. You should see 5 volts. (Could depend on the car and engine model, check a repair manual)
  5. If you are reading 12 volts, there is a short to the circuit that needs to be repaired.
  6. If there is no voltage, you can use a test light to probe the wire to see if it illuminates anywhere. If it does, there is a short with the ground connection.
  7. If there is no light across the connection, there could be an open circuit.
  8. There’s also the possibility that the PCM is to blame. 
  9. Additionally, if you can get 5 volts at the reference circuit, try to jump 5 volts to the EGR signal circuit. Your EGR position should read correct through the scan tool.
  10. Check the terminal tension at the valve connector. If the wiring looks okay, you need to replace the EGR valve. 

Estimated Cost of Repair

Here are a few of the expenses you might be dealing with.

  • Repair EGR position sensor wiring – $0-$150
  • Replace EGR position sensor – $100-$150
  • Replace differential pressure feedback electronic (DPFE) sensor – $150-$500
  • Check PCM connection/update software – $75-$150
  • Replace PCM – $400-$1,300

Mechanics Tips about the P0405 Code

Many of the same symptoms can occur when the EGR sensor or differential pressure feedback electronic sensor goes bad. It’s important that you perform the correct diagnostics and follow through with the right repair to ensure you aren’t stuck in the same situation in the end. 

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Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.