Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Garage soon
Code P0409: EGR sensor "A" circuit fault
P0409 means: exhaust gas recirculation (EGR) sensor "A" circuit.[1][2][3][4] P0409 is a generic OBD-II code that points to a fault in the exhaust gas recirculation (EGR) sensor "A" circuit. According to TAT, the control unit stores it when it detects an incorrect or out-of-range signal from the EGR valve position sensor (sensor 1), and the cause may lie in the sensor, the wiring or the valve itself. PartsAvatar adds that it often appears together with other EGR codes.[1][2]
What code P0409 means
P0409 is a generic OBD-II code that points to a fault in the exhaust gas recirculation (EGR) sensor "A" circuit. According to TAT, the control unit stores it when it detects an incorrect or out-of-range signal from the EGR valve position sensor (sensor 1), and the cause may lie in the sensor, the wiring or the valve itself. PartsAvatar adds that it often appears together with other EGR codes.[1][2]
Unlike P0405 (low signal) and P0406 (high signal), the definition of P0409 does not say whether the signal is low or high: it refers to the sensor "A" circuit in general. P0486 is the equivalent for sensor "B".[4]
The EGR sends part of the exhaust gas back into the intake to lower combustion temperature and reduce NOx. The control unit checks that it is working by watching a valve position sensor, a temperature sensor located downstream of it, or the change in manifold pressure when it commands the valve open; and, because the system itself feeds sooty exhaust gas into the intake, carbon deposits build up over time and can clog valves, passages and sensors.[5]
It is a generic OBD-II code (it starts with P0), so it means the same on any make; what changes from one engine to another is the most likely cause.[2][6]
Original definition (SAE J2012): Exhaust Gas Recirculation Sensor "A" Circuit[1][2][3][4]
Causes of P0409
From most to least likely, according to the sources.
- 1Faulty EGR valve position sensor, or one giving an out-of-range signal.[1][2]
- 2Damaged sensor wiring or corroded or loose connectors; AutoDTCs notes that, with EGR circuit codes, connectors close to the hot exhaust are a frequent cause.[1][2][5]
- 3Faulty EGR valve, or one with the pintle stuck closed by soot build-up.[1][2][5]
- 4On vacuum-operated EGR valves, lack of vacuum or a faulty vacuum solenoid.[1]
Symptoms
- Engine warning light on in the instrument cluster.[1]Engine warning light: faults that cause it
- Poor idle if the EGR pintle stays partly open.[1]Vibrations: faults that cause it
- The engine may stall if the EGR pintle stays partly open.[1]Engine stalls: faults that cause it
- Pinking or knock under load or at high revs.[1]
How to diagnose P0409
In order: from the most likely and cheapest to check to the most expensive.
- 1Connect a diagnostic tool, read the codes (stored, pending and active) and the freeze-frame data; then clear the code and road test in similar conditions to see whether it comes back.[1]
- 2Carry out a visual inspection of the EGR valve, its wiring and connectors and the vacuum lines, looking for corrosion, play, damaged wires or split hoses.[1][5]
- 3With the diagnostic tool, command the EGR to open and close and watch the position sensor signal: it should follow the valve with a smooth variation. With a multimeter, check the reference, earth and signal at the sensor connector.[1][5]
- 4Remove the valve and look for soot on the pintle, the seat and the passages. AutoDTCs warns that it is common to find valves that pass the electrical test but sit in front of a passage full of soot.[1][5]
- 5Repair or replace only what proves faulty (wiring, connector, sensor, valve or vacuum solenoid) and test the system again; AutoDTCs insists on inspecting before replacing parts.[1][5]
Can I keep driving with P0409?
Garage soon
The only source that rates urgency, AutoDTCs, classes P0409 as moderate: it should be repaired soon, although it does not normally leave you stranded. The other sources do not give a view. PartsAvatar points out that if the EGR pintle stays partly open, the idle may be poor or the engine may stall.[1][3]
Documented faults related to P0409
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
EGR valve: the most serious faults by engine and car
- Critical severityFrequency: Very frequentBMW B47EGR cooler leaks with risk of engine fireYes: the EGR valve cooler can suffer internal coolant leaks which, mixed with soot and oil, can reach combustion temperatures; BMW has launched several technical campaigns since 2018 to inspect and replace it because of the risk of engine fire.Repair (garage): €500–€1,500
- Critical severityFrequency: Very frequentBMW N57EGR cooler leaks with risk of engine fireYes: like the N47 and B47, the N57 is covered by BMW's service campaign for EGR cooler leaks, which can mix coolant with soot and oil to combustion temperatures. BMW checks free of charge the 6-cylinder engines built between July 2012 and June 2015 because of the fire risk.
- High severityFrequency: Very frequentOM651EGR and particulate filter clogging, and emissions software updatesThe particulate filter and EGR clog up with short journeys, as on any diesel with these systems. In addition, Germany's KBA required software updates on several models with this engine between 2018 and 2021 because of a function that reduced EGR outside a temperature range.Repair (garage): €800–€2,500
- Medium severityFrequency: Very frequentOM642Emissions defeat device (AdBlue/EGR) and software update campaignGermany's KBA found indications of emissions manipulation in cars with the OM642 engine (alongside the OM651): AdBlue dosing and the EGR changed between the test bench and the road. Mercedes-Benz denied it, but in 2018 it recalled hundreds of thousands of diesels in Europe.
Engine sensors: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- High severityFrequency: OccasionalM264/M254Poorly tightened 48 V earth wiring in the mild-hybrid system (fire risk)Mercedes-Benz has issued several recalls (2022-2025) because the 12 V and 48 V earth connections of some cars with a 48 V system may be poorly tightened: resistance rises, the connection heats up and a fire cannot be ruled out. The official workshop checks them and repairs them if necessary in an hour or more.
- High severityFrequency: Occasional1.9 TDIUnit injector tappet wear and injector wiring damageOn the unit injector system, the tappets that operate the injectors can wear if the oil is not changed on time, and the injector wiring can be damaged by contact with oil, causing misfires or loss of power.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
Frequently asked questions
What is the difference between P0409, P0405 and P0406?
All three are EGR sensor "A" circuit codes. P0405 indicates that the signal is low and P0406 that it is high; P0409 refers to the sensor "A" circuit without specifying the direction, and TAT describes it as an incorrect or out-of-range signal from the position sensor. P0407, P0408 and P0486 are the equivalents for sensor "B". In its EGR fault table, Pierburg lists P0405 to P0408 as a group, but not P0409.[2][4][7]
What is EGR sensor "A"?
TAT associates P0409 with the signal from the EGR valve position sensor (sensor 1), which tells the control unit how far the valve is open. The standard distinguishes a sensor "A" (P0405, P0406 and P0409) and a sensor "B" (P0407, P0408 and P0486). AutoDTCs adds that, depending on the system, the control unit may also check the EGR with a temperature sensor located downstream of the valve or with the change in manifold pressure.[2][4][5]
Can I drive with code P0409?
In the short term, normally yes, but it should be repaired soon. The only source that rates it, AutoDTCs, classes it as moderate and says it does not normally leave you stranded. If the EGR pintle stays partly open, PartsAvatar warns that there may be a poor idle or stalling.[1][3]
Will cleaning the EGR valve fix it?
Sometimes. PartsAvatar cites soot that leaves the pintle stuck as one of the causes, and AutoDTCs reminds us that it is common to find valves that pass the electrical test in front of a passage full of soot. But if the origin is the position sensor, the wiring or a connector, cleaning will not solve it; that is why it is worth checking the sensor signal and the wiring before removing anything.[1][5]
Will I pass the MOT with P0409 active?
If the code keeps the engine warning light on, no: according to Diariomotor, that light is a major defect in the ITV (the Spanish roadworthiness inspection, equivalent to the MOT) and, on Euro 5 and Euro 6 cars, the inspection also reads the OBD system.[8]
Does P0409 mean the same on all makes?
Yes. Codes that start with P0 are generic OBD-II codes (defined by SAE) and have the same definition at every manufacturer; what varies from one engine to another is the type of EGR valve and the part that tends to fail.[2][6]
Will I pass the MOT with code P0409?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[9]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- Error Code P0409: What It Means & What To Do?PartsAvatar · Technical documentation · published 14 March 2023 · consulted 2 October 2026
- P0409: EGR valve position signal error sensor 1The Automotive Technician (TaT) · Technical documentation · consulted 2 October 2026
- P0409 – Exhaust Gas Recirculation Sensor "A" CircuitAutoDTCs · Technical documentation · consulted 2 October 2026
- Generic OBDII P Codes P0400-P0499Rick's Free Auto Repair Advice · Other source · published 16 March 2024 · consulted 2 October 2026
- How to Diagnose EGR System Codes (P0401, P0402, P0403, P0406)AutoDTCs · Technical documentation · consulted 2 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 2 October 2026
- OBD-SystemMS Motorservice (Pierburg) · Manufacturer · consulted 2 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish