P0403: Exhaust gas recirculation (EGR) circuit malfunction
The engine computer has found a fault in the circuit that drives the exhaust gas recirculation (EGR) valve, so it can’t move the valve as it wants. The valve may be stuck open, closed or part-way.
Updated
What P0403 means
The exhaust gas recirculation (EGR) valve leads some exhaust gas back into the intake to lower the nitrogen oxide (NOx) emissions. The engine computer decides how much from the engine speed and load: petrol engines use little or none at idle and full load, diesels also use it at idle and light load. On many engines an electric motor or solenoid moves the valve, and a position sensor reports where it is.
P0403 means the engine computer found a fault in the circuit that drives the valve. It can’t move the valve as it wants, so the valve may stay where it is: open, closed or part-way.
P0400 and P0404 to P0409: EGR flow, valve movement and sensors
P0400 means the EGR flow isn’t as expected, without saying whether it’s too much or too little (P0401 and P0402 say that). P0404 means the valve doesn’t move as commanded. P0405 to P0409 are faults in an EGR sensor’s circuit: on many engines the position sensor built into the valve.
They get the same advice, because what the engine does depends on where the valve ends up. Their own meaning and causes are shown below.
P0400: Exhaust gas recirculation (EGR) flow malfunction
The exhaust gas recirculation (EGR) flow isn’t what the engine computer expects, without the code saying whether it’s too much or too little. On some cars the engine goes into limp mode.
Common causes: carbon-clogged or sticking egr valve, faulty egr valve position sensor, wiring or connector fault.
P0404: Exhaust gas recirculation (EGR) circuit range/performance
The EGR valve doesn’t move the way the engine computer commands it: it opens only partly, or the position it reports doesn’t match.
Common causes: egr valve sticking with carbon, faulty egr valve position sensor, wiring or connector fault.
P0405: EGR Sensor A Circuit Low
The signal from an EGR sensor, on many engines the position sensor in the EGR valve, is out of range or missing, so the engine computer can’t check what the valve does.
Common causes: faulty egr valve position sensor, faulty egr valve, where the sensor is built in, wiring or connector fault.
P0406: EGR Sensor A Circuit High
The signal from an EGR sensor, on many engines the position sensor in the EGR valve, is out of range or missing, so the engine computer can’t check what the valve does.
Common causes: faulty egr valve position sensor, faulty egr valve, where the sensor is built in, wiring or connector fault.
P0407: EGR Sensor B Circuit Low
The signal from an EGR sensor, on many engines the position sensor in the EGR valve, is out of range or missing, so the engine computer can’t check what the valve does.
Common causes: faulty egr valve position sensor, faulty egr valve, where the sensor is built in, wiring or connector fault.
P0408: EGR Sensor B Circuit High
The signal from an EGR sensor, on many engines the position sensor in the EGR valve, is out of range or missing, so the engine computer can’t check what the valve does.
Common causes: faulty egr valve position sensor, faulty egr valve, where the sensor is built in, wiring or connector fault.
P0409: EGR Sensor A Circuit
The signal from an EGR sensor, on many engines the position sensor in the EGR valve, is out of range or missing, so the engine computer can’t check what the valve does.
Common causes: faulty egr valve position sensor, faulty egr valve, where the sensor is built in, wiring or connector fault.
Can I keep driving?
Drive gently
Drive gently and have it checked soon. Depending on where the EGR valve is stuck, the engine can run rough or stall when you slow down or stop, or lose power (limp mode). Leave extra room in traffic until it’s fixed.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
A valve stuck open lets in more exhaust gas than the engine computer wants: a petrol engine can run rough or stall when you slow down or stop; a diesel may run rough, smoke or lose power. A valve stuck closed raises emissions and, on some petrol engines, the risk of knocking. Some engines go into limp mode either way.
Symptoms
- A rough or uneven idle, or stalling when you stop.
- Less power, or limp mode on some cars.
- Pinging when accelerating, on some petrol engines.
- Sometimes only the check engine light.
Common causes
- Faulty EGR valve or its actuator. The motor or solenoid that moves the valve can fail. On many engines the valve and its actuator are one part.
- Wiring or connector fault, or a blown fuse. The valve sits near hot exhaust parts, which age its plug and wiring.
- EGR valve stuck with carbon. Soot can jam the valve, especially on diesels and on cars used mostly for short trips.
Typical fixes
- Check the EGR valve’s plug and wiring, and its fuse.
- Have the valve’s motor or solenoid and its position sensor tested, and the valve checked for carbon.
- Clean or replace the valve, depending on what the tests show.
- Clear the code after the repair. Under emissions readiness, the EGR self-test shows when the car has re-tested the system.
Questions
Can I drive with P0403?
Gently, and have it checked soon. Depending on where the EGR valve is stuck, the engine can run rough or stall when you slow down or stop, or lose power, so leave extra room in traffic.
What is the difference between P0403 and P0401 or P0402?
P0401 and P0402 mean the EGR flow is too low or too high. P0403 means the computer can’t drive the valve properly because of an electrical fault, so the flow could be either.