Bosch-Common Rail System – Fuel injector solenoid valve

1 Solenoid armature
2 Wiring harness connector connection
3 Solenoid valve needle

The fuel injectors are each fitted with one solenoid valve. Actuation for fuel metering is carried out by the PCM.

The electrical supply of the solenoid valves occurs in several phases:
1. Opening phase,
2. Pickup current phase,
3. Transition to holding current phase
4. Holding current phase,
5. Turn-off phase,
6. Recharge phase

A Solenoid valve current
B Solenoid valve needle lift
C Injected fuel quantity
t Time
1 Opening phase
2 Pickup current phase
3 Transition to holding current phase
4 Holding current phase
5 Turn-off phase
6 Recharge phase

In the opening phase the current has to increase initially to approximately 20A with a steep edge to achieve a low tolerance and therefore high repeatability for calculation of the injected quantity.

This is achieved by using an amplifier voltage of up to 100 V which is generated in the PCM and stored in a capacitor.

By applying this high voltage to the solenoid valve, the current rises several times steeper than when battery voltage is applied.

In the pickup current phase the solenoid valve is supplied by battery voltage. This supports rapid opening of the solenoid valve.

Current control limits the pickup current to approximately 20A.

In the holding current phase the current is reduced to approx. 12A. Unnecessary heat generation in the PCM is prevented in this way.

When lowering the pickup current to holding current, energy is released. It is supplied to the capacitor (amplifier voltage storage) for recharging.

In the turn-off phase the current is switched off to close the solenoid valve. This releases energy which is also supplied to the capacitor.

The recharge phase takes place between injections. For this purpose, an unused solenoid valve is supplied with a saw-tooth current. The current level is so low, however, that the solenoid valve is not opened.

The energy stored in the solenoid valve is also supplied to the capacitor so that it is fully charged for the next opening phase.

Effects of faults

rough engine running,
increased emissions of black smoke,
loud combustion noise


The monitoring system is able to identify two types of malfunctions via several electrical tests.
• Fuel metering fault of all fuel injectors,
• Fuel metering fault of a single fuel injector

This works by monitoring the staged power supply (current phases) of the fuel injectors (as described previously).

The power consumption of the solenoid valve coil (in relation to a defined time) indicates whether the solenoid valve is working within its tolerances. Deviations from the tolerance range result in uncontrollable fuel metering. This means that the injected quantity and the injection timing cannot be determined exactly (see Possible consequences of faults).

In addition, the fuel injectors are checked for short circuit and open circuit. Fuel injector faults are MIL active if continued engine running is permitted.

Possible diagnostic trouble codes: P0201 to P0204 (MIL active); P1201 to P1204, P1551 to P1554 (non MIL active)

08. August 2018 by Ron
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