The P0400 code is displayed by your OBD-II scan tool if you detect a problem with the Exhaust Gas Recirculation system (EGR). If it detects a lower EGR flow than expected, the Powertrain Control Module stores the P0400 error code in its memory. The EGR valve is the heart of EGR system. The EGR valve’s main job is to send a part of the exhaust gases into the intake manifold so that they can be mixed with air/fuel. It reduces the cylinder temperature and nitrogen oxide levels (NOx). It may cause your vehicle’s emissions to increase if it malfunctions.
In older vehicles the EGR is directly controlled by the engine vacuum. Modern and newer vehicles are controlled by the PCM. The P0400 fault is set if the PCM detects exhaust gases not flowing into the intake manifold or flowing too slowly when it opens the EGR valve.
P0400 is more common in some vehicle models than others. If you have a Nissan, Mercedes Benz (especially a Nissan Frontier), Ford, Opel, or Subaru, and receive the P0400 error code, get your vehicle checked immediately by a technician.
Other codes related EGR faults include P0401, P0402, P0403, P0404, P0405, P0406, P0407, P0408, P0409
Table of Contents
What are the causes of the P0400 fault code?
It is possible that the cause of your P0400 code will vary depending on what model and make you have. Most common causes for an EGR flow failure or P0400 error are:
- Faulty EGR Valve
- Damaged cables or loose connectors can cause problems with the EGR valve circuit
- EGR Lines Clogged
- Vacuum lines damaged or disconnected
- Faulty EGR Temperature Sensor
- EGR Pressure Sensor Fault
- Update PCM if it is faulty or faulty
What are the symptoms of the P0400 fault code?
If the P0400 code is triggered, you may encounter issues with your vehicle’s drivability. Most common symptoms include:
- The engine fault light is illuminated
- Engine hesitating when accelerating
- Starting the engine is difficult
- The idle speed fluctuation
- Reduced engine performance
- Engine knocking and backfiring
- Fuel consumption increases
- Increased Emission Values
- Increased combustion temperatures can cause engine overheating
Some cases may not show any symptoms, other than an engine fault light.
How to Fix P0400 Fault Code?
As EGR valves are designed differently, one test is not enough. Test the EGR using a scanner tool while the motor is running. The problem will most likely be caused by faulty wiring or obstructions in the lines if the engine misfires. If there is no misfiring in the engine, you can test the EGR manually. All lines will need to cleaned and the valve removed.
- Checking cables and connections leading up to the EGR valve
- Checking the cables and connections leading to EGR temperature sensor
- Replace a broken vacuum hose leading to the EGR Valve
- Clean carbon deposits from EGR pipes leading into the intake manifold
- Replace or clean the EGR temperature sensors
- Replace the EGR Pressure Sensor
- Replace the EGR valve
How Serious is the P0400 Fault Code?
The EGR valve may malfunction, causing misfiring and damage to the pistons and valves of the engine. Vehicle emission values may increase, and the vehicle could fail an emissions test.
