Skip the auto shop - Our mechanics make house calls

P0409 OBD-II Trouble Code: Exhaust Gas Recirculation Sensor "A" Circuit

check engine light logo

P0409 code definition

P0409 is a generic OBD2 diagnostic trouble code pointing to an issue with the exhaust gas recirculation circuit. This code may be seen with other EGR codes.

What the P0409 code means

The P0409 code is set when there is a malfunction in the exhaust gas recirculation sensor A circuit. Low voltage from sensor A is detected by the ECU. This causes a Check Engine Light to be shown on the dashboard.

What causes the P0409 code?

  • Faulty EGR valve
  • Open or short in the wiring harness
  • Carbon Buildup on EGR valve
  • Failed EGR solenoid or position sensor

What are the symptoms of the P0409 code?

P0409 has a few typical symptoms. In all cases the Check Engine Light will be seen on the dashboard. The vehicle may experience a lack of power and a ping noise under heavy use. In some cases no adverse symptoms are noticed other than the Check Engine Light.

How does a mechanic diagnose the P0409 code?

  • Hooks up a scan tool tool to the DLC port on the vehicle and checks for any history, pending, or current codes.

  • Checks the freeze frame data which tells the technician under what conditions the DTC was set under

  • Clears the codes and takes the vehicle on a test drive under similar circumstances as the freeze frame data

  • Performs a visual inspection on the EGR valve, wiring, and vacuum lines.

  • Uses a scan tool to check EGR operation

  • Inspects the EGR for any carbon buildup or a stuck valve

Common mistakes when diagnosing the P0409 code

Mistakes are seen when steps are overlooked or not completed in the proper order. This can cause the replacement of parts that work fine wasting time and money.

How serious is the P0409 code?

The P0409 can be a minor annoyance but should not prevent the vehicle from being driven to a safe location once the code is seen. The EGR system is used to recycle exhaust gases back into the intake to help with emissions and will prevent the passing of OBD2 emissions while P0409 is present.

What repairs can fix the P0409 code?

  • Replacing the EGR valve
  • Decarbonizing the EGR valve
  • Repairing or replacing the wiring harness
  • Replacing the EGR solenoid
  • Replacing the EGR position sensor

Additional comments for consideration regarding the P0409 code

In cases where the EGR valve is stuck open or closed with carbon buildup this can be removed with cleaners which will fix the problem in some cases. A throttle body cleaner can be used to remove the carbon buildup and restore EGR valve operation.

Need help with a P0409 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
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Post a question and get free advice from our certified mechanics.

ASK A QUESTION

More related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed Related Trouble Codes: P2441: EVAP Vent Valve Stuck Open EVAP trouble...


Related questions

Q: Whilst driving the car will cut out. In the begining it would start immediatetly now if it cuts out it doesnt want to start

Hello. I would need to know the model of your Toyota to be able to give you the best information. From what you are telling me though it sounds like the crank sensor harness may be damaged or that one...

Q: Car starts, dashboard lights flicker, air conditioning shuts off

Hello there, thank you for asking about your 1993 Isuzu Pickup. It sounds like a bad ground in the instrument panel circuit. Looking at the wiring diagram, I see the AC heater control panel and instrument cluster share the same...

Q: Malfunction Transmission light appeared on dashboard

Automatic transmissions can be tricky. Luckily, as odd as it seems, the fact your vehicle is setting a warning light is a good thing. This allow you to run a diagnostic scan for trouble codes, and will help narrow down...