On account of the high loads it has to withstand, the EGR valve is doubtless the biggest source of faults. Oil mist and soot from the exhaust emissions impede the valve, and the cross section of the valve opening reduces over time until it completely closes up. This causes a steady reduction in the recirculated quantity of exhaust emissions, and this is reflected in the exhaust emission performance. The high thermal loads further facilitate this process. In many cases the hose system for the vacuum is also a cause of faults. The vacuum required for the EGR valve can be lost due to leaks, meaning the valve no longer opens. If the EGR valve is not working due to a lack of vacuum, this may, of course, also be caused by a faulty pressure transducer or a thermovalve that is not working properly.
There are several ways of checking the exhaust gas recirculation system. Which method you choose depends on whether or not the system is capable of running self-diagnostics. Systems which are not capable of running self-diagnostics can be checked using a multimeter, a manual vacuum pump, and a digital thermometer.
However, before you start running complex tests, conduct a visual inspection of all system-related components. This means checking the following:
- Are all vacuum lines leak-tight, correctly connected, and routed without kinks?
- Are all electrical connections on the pressure transducer and change-over switch correctly connected? Are the cables OK?
- Are there any leaks on the EGR valve or the connected lines?
If no defects are found during the visual inspection, check the system using other tests and measurements.
The following procedure applies when checking vacuum-controlled EGR valves: