What is the P0408 fault code What is the description of Exhaust Gas Recirculation (EGR) Sensor “B” Circuit High malfunction? How can you fix the P0408 fault code What are the symptoms and causes for the P0408 fault code
What is the P0408 Fault code? What does it mean
A code P0408 is triggered when the powertrain controller module (PCM), detects an excessively high voltage signal from the exhaust gases recirculation sensor circuit (EGR), which exceeds the manufacturer’s threshold.
The EGR system lowers combustion temperatures in certain conditions and reduces nitrogen oxide (NOx), emissions. It does this by returning inert exhaust gases to the cylinders, where they are burned with the mixture of air and fuel. Inert exhaust gas burns at a lower temperature which reduces the engine’s combustion temperature. This lowers nitrogen oxide emissions.
While some EGR systems can be quite simple, others are more complicated. An electric EGR valve is controlled by the PCM directly via a harness. These valves may have four or five wires. The ground circuits are typically 1 or 2 ground, 12 volt power supply and 5 volt reference, as well as 1 feedback circuit. The vacuum-controlled EGR valves can be operated by a vacuum pump. The PCM controls the vacuum solenoid that opens or closes the EGR valve. These EGR valves are equipped with an electrical connector that provides feedback. The PCM uses the feedback loop to control its valve’s position.
The PCM should be able to detect the presence of a certain amount of manifold pressure change when the EGR is activated. It will set fault code P0408 if it detects an air pressure change that is not within the acceptable range.
This code is almost identical to P0406. The only difference is that P0406 fault code refers to an “A” sensor, while P0408 points at a “B” sensor. The location of the “A”, “B”, and other sensors can be found in the vehicle’s specific repair manual.
The P0408 fault code can affect vehicles of all makes and models, including but not limited to: Fiat, Mitsubishi (VW), Volkswagen, Audi, Seat Skoda Citroen Peugeot, Fiat, Fiat, Fiat, Fiat, Mitsubishi, Volkswagen, Audi.
What causes the P0408 Fault code?
Below are some reasons to set fault code P0408.
- – Damaged or defective EGR temperature sensors
- – A fault in the circuit for the EGR temperature sensor
- – Broken wires or loose connectors that are open to the EGR valve circuit.
- – Excessive carbon buildup at the EGR valve
- – Defective EGR solenoid
- – Defective EGR valve
What are the symptoms of P0408 Malfunction Code?
These symptoms may be present in vehicles with code P0408.
- – Illumination for check engine light
- – Variations in engine speed while driving
- Engine stalling in some situations
- – Reduced engine performance
- – Exhaust emissions are rising
- – Increased fuel consumption
How do I fix the P0408 fault code?
There are several repairs that can resolve the P0408 fault code:
- – Replacing the EGR temperature sensors or repairing them
- Repairing short or open circuits in the EGR sensor circuit and replacing damaged wires or connectors
- – Removing carbon deposits from EGR valve
- – Replacing the EGR solenoid.
- – Replacing the EGR valve that is faulty
Special cleaning sprays can be used to clean the EGR valve if it is stuck open or closed due to carbon deposits. Most cases this will resolve the issue.
How Serious Is the P0408 Fault Code
The code won’t prevent you from being on the road. However, if this code is triggered, then the PCM will disable EGR. The vehicle’s emission levels will rise as the engine fault light illuminates. You can avoid potential failures by addressing the problem as soon as possible.
