641 Testing The Egr Sensor

In order to avoid injury it is recommended that the test is performed on a cold engine. This is only possible where the EGR valve can be lifted from its seat manually. The type of voltage trace that can be expected from this type of sensor is shown in Fig. 6.9. In order to obtain a voltage trace the sensor must be energized and it is always wise to check that the supply voltage to the sensor is correct.

If it is necessary to perform the test under load, the scope connections should be made secure and the test instrument placed in a secure position so that the pattern can be observed without risk of personal injury from either the dynamometer, or the moving parts of the vehicle. If the test is performed during a road test it is essential that an assistant accompanies the test driver.

The valve that controls the vacuum that energizes the EGR valve is often controlled by a solenoid which, in turn, is controlled by the ECM. Figure 6.10 shows the connections for the oscilloscope for this test and Fig. 6.11 shows a typical duty cycle trace for the EGR valve.

As the duty cycle may be increased or decreased by the ECM, the operation of the EGR valve is controlled to permit varying quantities of exhaust gas to be transferred from the exhaust system into the intake system.

Idle speed control is an important element of the control strategy for any engine management system. The control strategy for engine idling must take account of factors such as engine coolant temperature, engine load, power assisted steering, alternator load, etc. Many systems are fitted with an idle speed control valve that provides a supply of air that by-passes the throttle valve, whilst other systems

1 EGR valve closed restricting the flow of exhaust gas,

2 EGR valve open nearly all the way allowing flow of exhaust gas.

1 EGR valve closed restricting the flow of exhaust gas,

2 EGR valve open nearly all the way allowing flow of exhaust gas.

Fig. 6.9 An impression of the voltage trace from an EGR sensor

6.5 Retro! engine idle speed control

Fig. 6.10 Making the connections for the test on the EGR valve

600 Hz

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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