P0409

What it means

P0409 is the generic SAE J2012 code for a fault in the EGR Sensor 'A' circuit, usually the exhaust gas recirculation valve position sensor or pressure sensor depending on the system design. The engine control unit set it because the signal voltage from that sensor was outside the expected range, implausible, or did not match the commanded EGR valve position.

Symptoms

• Engine management light on
• Rough or unstable idle
• Hesitation or poor acceleration
• Engine pinking or knocking under load
• Slightly higher fuel consumption
• Occasional stalling at idle or when coming to a stop

Possible causes

• Carbon-fouled or sticking EGR valve affecting the integral position sensor readinglikely
• Faulty EGR position or pressure sensor (internal failure or drift)likely
• Damaged, chafed or corroded wiring to the sensor, including open circuit, short to earth or short to supplylikely
• Poor connector contact, with bent, loose or corroded terminals or water ingresspossible
• Blocked or leaking EGR pressure sensor hose or pipe (on systems that use a differential pressure sensor)possible
• Fault in the sensor reference voltage or earth supply from the control unitrare
• Internal fault in the engine control unitrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data to see engine load, speed and temperature when the fault set, and note any related EGR codes.
2. Check the manufacturer's information for how this model's EGR sensor 'A' is arranged, as it may be a valve position sensor or a pressure sensor depending on make and engine.
3. Visually inspect the sensor, wiring loom and connector for chafing, heat damage, corrosion, water and pushed-back or bent pins.
4. With live data, compare the commanded EGR position with the actual sensor reading at idle and when the valve is commanded open and closed, if the system allows.
5. Check the sensor supply voltage, signal and earth at the connector against the manufacturer's specification.
6. Test the wiring for continuity and for shorts to earth or supply between the sensor and control unit.
7. Remove and inspect the EGR valve and passages for heavy carbon build-up or a valve that sticks or fails to return, and check any pressure sensor hoses for blockage, splits or loose fittings.
8. Once repaired, clear the codes and road test, then recheck live data and for returning codes.

How to fix

• Repair or replace damaged wiring and terminals, and secure the loom away from heat and sharp edges.
• Clean or replace the connector terminals, or replace the connector if it is corroded or damaged.
• Clean the EGR valve and passages if carbon is the cause, or replace the valve if it sticks or the position sensor is integral and faulty.
• Replace the EGR position or pressure sensor if it tests faulty and is available separately.
• Replace blocked, split or perforated pressure sensor hoses or pipes.
• If all wiring and components test good, have the control unit supply and signal checked, and repair or replace the unit only after confirmation.

Can I keep driving?

Nearby codes

• P0408GenericEGR Sensor B Circuit High
• P040AGenericEGR Temperature Sensor A Circuit