Virtual Tour of a 2G DSM Engine Bay: Solenoids

This are a group of solenoids that the engine control unit (ECU) uses to control engine operation. Although none of them are critical, they are not completely useless either.

The solenoids shown are stock; the hoses connecting to them are not. Stock hoses are black.

When you are facing the engine bay, the left-most solenoid is the exhaust gas recirculation (EGR) control solenoid. It is indicated by the white arrow. It controls the flow of exhaust gas through the exhaust gas recirculation valve - a valve that allows some exhaust gases to run back into the intake stream. This is purely for emissions purposes, as "reburning" some of the exhaust gas helps reduce emissions.

The first solenoid, marked with a yellow arrow, is the purge control solenoid valve. It controls an air connection between the evaporative emissions charcoal cannister and the intake system. The charcoal cannister is designed to absorb fuel vapours that come from the fuel tank for emissions purposes. The purge solenoid allows the ECU to connect the cannister to the engine intake - when connected, the gasoline vapours are drawn in to the engine and burned off. The solenoid is there so that the outlet from the cannister may be closed when the car is not running.

The right-most solenoid, marked with a green arrow, is the fuel pressure solenoid. This solenoid allows the engine control computer to temporarily raise the fuel pressure for hot starting purposes. This is accomplished by cutting off the vacuum hose going to the fuel pressure regulator. It is not used for anything else, but it can provide a useful tap-in point for a boost gauge, since the regulator "sees" the intake manifold pressure. (If you tapped your boost gauge in here, but it doesn't read any vacuum right after warm or hot starts, you probably connected to the wrong side of the solenoid.)

First-generation cars are a little different in that all three solenoids are grouped together to the right of the brake master cylinder, and the order gets changed around. Their functions remain the same.