Testing EGR Systems (Exhaust Gas Recirculation) - Pt 2

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Testing EGR Systems (Exhaust Gas Recirculation) - Pt 2 September 2012

With the variety of EGR systems used for the control of NOx emissions it is important to understand the components operation, prior to carrying out any diagnostic or testing. (Refer to previous issues for EGR system operation).

Testing times for EGR systems

A defective component in the EGR system may have a very detrimental effect to the engine performance and therefore the emissions.

Strict emission laws and the malfunction indicator light generally illuminated when a system fault exists, require a prompt resolution.

1. Pneumatic EGR Valve System Component Tests

Note that vacuum supply to all components must be tested on the vehicle to eliminate misdiagnosis

Single diaphragm type EGR valve Using a manual vacuum hand pump can verify movement of the valve and the condition of the diaphragm. This can be performed on or off the vehicle. Dual diaphragm types will vary in test procedure.

EGR valve with potentiometer feed back Potentiometer resistance can be checked with the harness disconnected. Voltage test is preferred with the harness connected using a suitable scanner / scope or multimeter.

Electro-Pneumatic Vacuum Pump Valve Using the vacuum pump can verify if the valve is sealed or leaking when not activated and if the valve opens when the solenoid is activated. Solenoid resistance can also be tested with an ohm meter.

Thermo Valve Using the vacuum pump can verify if the valve is closed when cold and heating the unit with a heat gun should result in the valve opening above approximately 70 degrees Celsius.

2. Electric EGR Valve Test

The combination EGR valve and feedback system in this unit is controlled and monitored by the ECM and requires no external vacuum source to operate.

Note: This is a typical vehicle pin out configuration but this can vary for different vehicle models. Always refer to correct wiring diagram.

A suitable scanner can assist in testing this type of EGR valve by using the scanner program to activate the solenoid and also monitoring the feedback signal. The switching of a functioning valve can be audible when the engine is not running.

On later vehicles, renewing the EGR valve requires relearning by using program options in the scanner. That is the electric EGR valve must be adapted to the ECU.

Tips for troubleshooting EGR – Its Exhausting! The most common cause of malfunctions in the EGR systems are stuck or blocked EGR valves due to excess carbon build up. This generally results in incorrect sealing between the exhaust and inlet and results in idling problems and poor performance.

In most cases the EGR valve is replaced but the cause of the excess carbon is not investigated, why?

Engine Management systems where an Intake Air Temperature (IAT) sensor is located directly in the inlet manifold can assist greatly is diagnosing leaking EGR valves.

That is, monitoring the IAT output signal from a cold start – idling condition, should not indicate rapid increase in intake air temperature.

This would be the case if the EGR valve was allowing exhaust gas to enter the inlet manifold when not required.

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