P0407 OBD-II Trouble Code: Exhaust Gas Recirculation Sensor B Circuit Low

check engine light

P0407 trouble code definition

A P0407 trouble code is related to a vehicle’s exhaust gas recirculation (EGR) system that helps an engine control and reduce emissions. Consisting usually of a computer controlled valve that recirculates a metered amount of exhaust gasses back into the engine to be burned with the air/fuel mixture, an EGR system is only triggered under certain conditions and is either controlled directly by the engine computer, or uses a vacuum solenoid to be activated. The “B” sensor refers to a manufacturer’s location of the sensor.

What the P0407 code means

P0407 is an OBD-II generic code for a voltage problem with the EGR system in that the signal being sent from the circuit to the engine computer is unusually low and not within the manufacturer’s accepted parameters.

What causes the P0407 code?

While a P0407 can be caused by grounding issues or even a bad engine computer, the biggest culprit typically is the EGR valve itself. Other likely causes include:

  • Faulty EGR vacuum solenoid
  • Faulty EGR valve
  • Ground short in the EGR circuit
  • Voltage short in the EGR circuit
  • Bad wiring from the engine control unit to EGR system
  • Faulty engine control unit

What are the symptoms of the P0407 code?

Most engines do not need EGR systems to operate properly as it’s strictly for emissions standards. This means that if a P0407 comes up, chances are high that a driver won’t notice any ill symptoms other than a Check Engine Light. In some cases, diminished fuel mileage may occur or there may be slight hesitation under acceleration.

How does a mechanic diagnose the P0407 code?

Using a professional OBD-II scanner, a mechanic will typically monitor the EGR valve and see if it responds to feedback i.e. opens and closes. If it does, it may indicate that the valve simply needs to be cleaned. This can be done by removing the valve (usually near the exhaust and or intake manifold) and spraying carburetor cleaner and using a small brush. By reinstalling the valve, clearing the code, and driving the vehicle with a scan tool connected, a mechanic can monitor to see if the valve operates any differently as a result of the cleaning. If not, a multi-meter will help determine if the valve is getting the 5 volts it needs for a reference and feedback circuit. Bad wires may need to be replaced. If all of this checks out, the solenoid should be next. This can be tested by unplugging the output vacuum line and triggering the EGR valve to open. An audible tick should be heard from solenoid. If not, it may need to be replaced. If the solenoid is working properly though, chances are high the EGR valve is faulty.

Common mistakes when diagnosing the P0407 code

Oddly enough, the EGR valve is not always the cause of a P0407 and hastily replacing one without proper diagnosis can be expensive. You should test the least expensive components first such as wiring and solenoid before replacing the valve itself. A cleaning is much less expensive than a replacement.

How serious is the P0407 code?

A faulty EGR valve can increase your vehicle’s emissions and may affect its performance, but it usually won’t cause any seriously adverse side effects. You’ll want to have it inspected sooner than later but a few brief trips with a P0407 won’t cause any serious damage.

What repairs can fix the P0407 code?

The most common repairs for a P0407 are as follows:

  • Clear the code with a scanner and monitor for the code to return.
  • Visually inspect the EGR valve and associated wiring and vacuum lines for any obvious issues.
  • Clean the EGR valve, clear the code and monitor for it to return.
  • Check voltage and ground – repair wiring as needed.
  • Check vacuum lines to the EGR and EGR solenoid – repair as needed.
  • Force the solenoid to trigger on and off to check if it is working properly.
  • Replace EGR valve.

Additional comments for consideration regarding the P0407 code

A P0407 is not an engine code that should cause panic but it shouldn’t be ignored either as EGR systems play an important role in cutting down a vehicle’s overall carbon footprint. Most valves will be easy to find as they’ll typically be close to an engine’s intake manifold so the exhaust gasses can be recirculated. For some used vehicles, previous owners may have removed these systems out of convenience so keep that in mind.

Need help with a P0407 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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