Siemens-Common Rail System – EGR valve (electrically controlled systems)

A Installation position on 1.4L Duratorq-TDCi (DV) diesel engine (Emission Standard IV)
B Installation position on 2.0L Duratorq-TDCi (DW) diesel engine

Depending on the engine version, an electrically controlled EGR valve is used in the Siemens Common Rail system.

This EGR valve comprises the following components:
• Servo motor,
• Position sensor,
• the EGR valve itself.

Exhaust gas recirculation is further optimized by means of the electrically controlled EGR valve, which has a positive effect on exhaust gas emissions.

With the introduction of Emission Standard IV, an electrically controlled EGR valve is installed in all versions.

The illustration shows an excerpt of the circuit diagram of the 2.0L Duratorq-TDCi (DW) diesel engine

1 PCM
2 DC motor
3 Servo motor
4 Position sensor

NOTE: Following replacement of the EGR valve or replacement/reprogramming of the PCM, 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 via pulse width modulation.

The exact position of the EGR valve is determined via the position sensor.

It is therefore a closed-loop control circuit.

Note: Each time the engine is stopped, a cleaning/adaptation 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 point is reconfigured each time the engine is stopped. Consequently, the position sensor maintains its ability to perform precise measurement after long periods of operation.

Note: In some versions cleaning/adaptation mode can be observed with the help of a WDS datalogger.

Effects of faults

In the event 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:
• Monitoring of the DC motor,
• Monitoring of the position sensor,
• 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 for the following:
• Power consumption of the motor (excessively high or low current flow through the coil).
• Cleaning diagnosis of the EGR valve

The power consumption of the coil is used as a basis to check whether the signal from the PCM is within the limits. Moreover, potential overheating of the EGR valve is detected via the resistance of the coil.

Cleaning diagnosis is also performed via the power consumption of the DC motor. During cleaning, the DC motor must open and close the EGR valve within a defined timeframe. A sticking EGR valve is detected via the power consumption of the motor.

The position sensor is monitored for the following:

• limit range check: detects short and open circuits.
• logical rise/fall rate of the signal: by this means, intermittent errors (e.g. loose connector contact) are determined.
• plausibility check: detects a seized or sticking EGR valve

The plausibility check is started when a certain engine speed is reached.

If a control deviation of more than +20 % or –30 % with regard to the calibrated values is detected during the check, this is interpreted as a fault by the PCM and a relevant DTC is stored.

Therefore, this is a MIL active component.

Possible diagnostic trouble codes (DC motor): P0403, P0404, P1193.

Possible diagnostic trouble codes (position sensor): P0403, P0404, P0405, P0406, P0409, P0489, P0490, P1335, P1409, P141A.

01. September 2018 by Ron
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