The EGR valve is fitted on the exhaust side of the engine on the cylinder head.
The EGR valve comprises the following components:
โข Servo motor,
โข Position sensor,
โข the EGR valve itself.
1 PCM
2 DC motor
3 Servo motor
4 Position sensor
NOTE: After the EGR valve is replaced or after the PCM is replaced/reprogrammed, the EGR valve must be initialized by the PCM via WDS.
The servo motor acts as a DC motor that sets the requested opening cross-section of the EGR valve. Actuation is by means of the PCM using pulse width modulation.
The exact position of the EGR valve is established via the position sensor. It is therefore a closed control loop.
Note: Each time the engine is stopped, a cleaning mode is activated by the PCM, whereby the EGR valve is moved from its fully open position to a completely closed position (by means of maximum activation of the DC motor).
However, the longer the engine is in operation, the greater the likelihood of residues forming on the valve seat of the EGR valve as a result of the exhaust gases flowing past it. These residues can cause the mechanical closing point of the EGR valve to shift.
For this reason, the closing is re-adapted at regular intervals. Consequently, the position sensor also retains its precise measurement after a long period of operation.
Effects of faults
In the case of a fault, controlled exhaust gas recirculation is no longer possible and the EGR system is switched off. If the EGR sticks open, this is detected by the position sensor and the PCM then reduces the quantity of fuel injected and thus engine performance.
Diagnosis
Monitoring of the EGR servo motor is divided into three monitoring operations:
โข Monitoring of the DC motor,
โข Monitoring of the position sensor,
โข Monitoring of the EGR valve.
In addition, the entire EGR system (interaction between the EGR valve, position sensor, servo motor and MAF sensor) is monitored under certain operating conditions. The DC motor is monitored through a simple electrical test.
The output stage in the PCM for the DC motor is continuously checked for short circuit and open circuit, as well as for malfunctions that can occur due to high temperatures.
The position sensor is monitored for the following:
โข Limit monitoring: The PCM checks constantly if the incoming signal is within the limits.
โข Monitoring for short circuit and open circuit,
โข Position sensor reference voltage monitoring.
The position sensor also detects when the EGR valve is sticking in the open position. This is detected by adaptation of the mechanical closing point. For detection, the valve has to move a certain distance from its fully opened state to its fully closed state. If the expected distance is not traveled as programmed, the position sensor detects this and interprets it as a fault.
Another control function checks whether the position of the EGR valve is reached according to the requirements. This monitors proper mechanical functioning of the EGR valve.
Faults in the EGR valve have serious effects on the exhaust gas emissions. If the level of exhaust gas is too low, the NOX emissions increase, if it is too high, the diesel particulate emissions increase dramatically. Therefore, this is a MIL active component.
Possible diagnostic trouble codes: P0403, P0404, P0405, P0406, P1412.