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P0409: EGR sensor A circuit malfunction

The ECU sees a fault in the EGR sensor A circuit, without the signal being clearly high or low. Usually wiring, the connector or the sensor.

Code P0409 at a glance
CodeP0409
SystemEngine and transmission
GroupP04xx, Emissions control
TypeGeneric: it means the same on every make
Can you keep driving?With care

What P0409 means

EGR sensor A tells the ECU how exhaust gas recirculation is working; exactly what it measures is up to each manufacturer. Here the ECU has seen an inconsistent, intermittent or missing signal in its circuit.

Most common causes

  • Loose, corroded or slack pins on the sensor connector
  • Wire broken inside the insulation or chafed
  • Poor sensor earth
  • Faulty EGR sensor
  • Carbon jamming the valve so the sensor sees no movement

Symptoms

  • Engine warning light on
  • Rough idle
  • Slight loss of power
  • Sometimes no symptoms

Can you drive with P0409?

With care You can drive. The engine may run a bit worse and the EGR may be disabled, so have it checked soon.

How to check it

With the engine idling, gently wiggle the sensor wiring while watching its value on your reader: if it jumps or drops out, there is a poor connection.

How to read and clear P0409 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0409 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

P0409 is a generic code, so it means the same on any make, for example on Audi, Fiat, Mazda, Opel / Vauxhall, Peugeot, Toyota. See what Final OBD does on your car in makes and models.

What does code P0409 mean?

EGR sensor A tells the ECU how exhaust gas recirculation is working; exactly what it measures is up to each manufacturer. Here the ECU has seen an inconsistent, intermittent or missing signal in its circuit.

Can you drive with P0409?

You can drive. The engine may run a bit worse and the EGR may be disabled, so have it checked soon.

How do you clear P0409?

With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0409 comes back.