Aftermarket March 2022

BY Damien Coleman, Product Manager/ EBI Specialist at Snap-on A ctuators on modern vehicles can be difficult to diagnose, with many technicians resorting to replacement rather than diagnosing the component correctly. However, by using a methodical fault-finding process, we can quickly and accurately diagnose these components. Actuators can be controlled by a vacuum solenoid or a reverse polarity DC motor. In the next issue we will investigate the operation of motor control. Getting back to today, in this issue we will test a vacuum operated solenoid used for controlling the wastegate on a turbocharger fitted to a 1.5L K9K Renault engine. This is a compression ignition engine, so the intake manifold pressure never becomes negative (vacuum) due to the absence of a conventional intake throttle. These engines due use a throttle valve to manipulate intake manifold pressure for exhaust gas recirculation (EGR), diesel particulate filter (DPF) regeneration and shutting the engine off smoothly. Testing the electrical and pneumatic operation of a vacuum-operated valve can be beneficial when troubleshooting issues such as over and under boost concerns. 30 AFTERMARKET MARCH 2022 TECHNICAL/SNAP-ON www.aftermarketonline.net TESTING A VACUUM: OPERATED SOLENOID VALVE This issue, Damien is showing how a methodical process will mean a successful diagnosis on an actuator-related problem System operation Fig.1 shows the electrical operation of the turbocharger. The diagram illustrates the ‘command’ and ‘feedback’ part of the circuit. The turbo boost control solenoid has a constant supply (system voltage) from the engine bay fusebox and is controlled on the ground side by the engine control module (ECM). Closed loop control is via the turbo boost pressure sensor. This component has a constant 5-volt supply and ground from the ECM. The signal wire has a 5-volt biased voltage from the engine control module which is manipulated by an integrated circuit, within the sensor, to Actuators can be controlled by a vacuum solenoid or a reverse polarity DC motor ”