Fault code P0407 – exhaust gas recirculation sensor “B” circuit low

Fault code P0407 is called “Exhaust Gas Recirculation (EGR) Sensor “B” Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0407

Error P0407 refers to a fault in the exhaust gas recirculation (EGR) sensor circuit. Displayed when the Powertrain Control Module (PCM) detects a low signal level in the electrical control of the sensor.

Fault code P0407 – exhaust gas recirculation sensor "B" circuit low

The exhaust gas recirculation system is an integral part of the vehicle exhaust system. Its function is to prevent the formation of NOx (nitrogen oxides) in the cylinders in particular.

EGR is controlled by the vehicle’s computer, which opens or closes the exhaust gas recirculation system depending on load, speed and temperature. To keep the cylinder head at the proper temperature.

There are two wires that control and communicate with the computer. There are a total of 5 wires to the solenoid. Another 2 are battery voltage and ground. As well as one 5 volt reference terminal, usually located in the center.

If the engine computer, sees a low signal when it tries to open or close the EGR valve, it is perceived as an error. Code P0407 is then written to memory as a low signal on the EGR “B” sensor.

This means that the changes in the electrical circuit are below the reference values or are absent at all. The level of these values may vary depending on the make and model of the vehicle.

Unleaded fuel is prone to NOx (nitrous oxide) formation at extreme engine cylinder temperatures. The exhaust gas recirculation system sends a controlled amount of exhaust gas back to the intake manifold.

This is done to sufficiently dilute the incoming fuel mixture. This is to reduce the cylinder head temperature below the temperature at which NOx is generated.

Proper operation of the exhaust gas recirculation system is not only necessary to prevent NOx emissions. It also provides the engine with more power without detonation and a leaner fuel mixture for better fuel economy.

Symptoms of vehicle malfunctions

The main signal that an error P0407 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be written to the ECM memory as a fault).
  2. Engine stalls or starts poorly.
  3. Floating revolutions, as well as attempts to stall at idle.
  4. The vehicle engine may become unstable.
  5. Increased fuel consumption.
  6. Decrease of the engine power.
  7. Sometimes there may be no symptoms, despite the stored fault code.

The severity of code P0407 is high, but if there are no other symptoms besides the malfunction indication, the problem is considered to be moderate. But this should not become a factor for not solving the problem.

Factors that can cause this error code

The error code P0407 can mean that one or more of the following problems have occurred:

  • Short circuit to the ground.
  • Wiring problem or damaged connector.
  • Corrosion of electrical wires or connections.
  • Clogged exhaust gas recirculation valve ducts.
  • The exhaust recirculation system vent is clogged.
  • Exhaust differential pressure sensor ducts may be clogged.
  • Damaged vacuum lines or hoses.
  • Faulty exhaust gas recirculation valve position sensor or absolute air pressure sensor in intake manifold.
  • Excessive accumulation of soot, which prevents free movement of EGR valve.
  • Defective EGR.
  • In rare cases, malfunction of engine control module (ECM).

How to fix or reset OBD-2 code P0407

Some suggested steps for troubleshooting and fix the error code P0407:

  1. Connect an OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
  2. Clear the error codes from the computer memory and test-drive the vehicle to see if code P0407 appears again.
  3. If the error code appears again, visually inspect the electrical wires and connectors related to the exhaust gas recirculation system.
  4. If necessary, repair or replace any shorted, broken, damaged, or corroded components.
  5. If the problem persists, check the exhaust gas recirculation system passages for blockage. Inspect the vacuum lines and check thoroughly for vacuum leaks.
  6. Check the operation of the exhaust gas recirculation valve and the vent control solenoid valve.
  7. Check the operation of the exhaust recirculation valve position sensor and the absolute intake manifold air pressure sensor.
  8. Measure the voltage of the system vent control solenoid valve circuit using a digital multimeter.
  9. Compare value with manufacturer’s data sheet, replace faulty valve if necessary.
  10. If problem persists, check and replace engine control module (ECM) if necessary.

Diagnose and repair of problems

The first step in the P0407 troubleshooting process is to review the Technical Service Bulletins (TSB). For known problems with a particular vehicle.

The advanced diagnostic steps are very vehicle specific. It may require, special equipment and knowledge to accurately perform the steps.

Allow your vehicle’s engine to cool down. In most cases, exhaust gas recirculation (EGR) systems are very hot. Since they are usually installed directly on the exhaust system. Therefore, if you don’t let the engine cool down, you can get burned.

Inspect all vacuum lines, they don’t tolerate high temperatures well, and it’s not uncommon in a recirculation system. Any burned or broken vacuum line should be replaced or repaired.

Lines are inexpensive, so it is best to replace all lines with new ones, especially if you find that one has failed. If one has severe wear and tear, it is likely that the others will need to be replaced soon, too.

Check electrical circuits and connections

Be sure to carefully check the integrity of the wiring harnesses involved. They often run along and around the exhaust pipe. Therefore, it would be a good idea to tie off any loose wires. If you find a burned wire, solder the connections and make sure they are properly insulated.

Inspect the vent solenoid for cracks and water intrusion. Also, make sure that the connectors are properly electrically connected and that the latches are not damaged or broken.

If available with access, you can remove the exhaust recirculation valve to check its condition. These valves are susceptible to significant soot buildup. Use carburetor cleaner and a toothbrush to remove soot from any soiled areas.

If the most common tests do not solve the problem with error P0407. You should refer to your vehicle’s service manual to continue checking the electrical circuits.

On which vehicles does this problem occur most frequently

Fault code P0407 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi (A4)
  • Cadillac (SRX)
  • Ford
  • Hyundai (Solaris)
  • Land Rover
  • Mazda (3)
  • Mercedes-Benz
  • Skoda (Octavia)
  • Ssangyong
  • Volkswagen (Caddy, Golf, Passat, Polo, Touran)

Fault code P0407 can sometimes be found with other errors. The most common are the following: P0236, P0335, P0341, P0400, P0401, P0402, P0403, P0404, P0405, P0406, P0408, P0409, P0642.

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