Powertrain Management: Testing and Inspection

Fault In The Vacuum System

Introduction
This document describes the components of the vacuum system and frequently occurring causes of faults on the vacuum system.

Vacuum hoses
The vacuum hoses transport the partial vacuum to the pressure converters / changeover valves and to the actuators. Leak-tightness and no blockage of the vacuum hoses are decisive for the function of the system.
The vacuum hoses must be checked for the following faults:
- Kinks
If the vacuum hoses are routed in radii that are too tight or over edges, kinks can occur.

- Squashed vacuum hoses
The vacuum hoses can be squashed by contacting components (for example acoustic cover).

- Cracks
Especially at the ends of the vacuum hoses, cracks can arise that lead to leaks.

NOTE: Cracks can be covered by the hose fabric.







Changeover valves, pressure converters
The changeover valves and pressure converters switch the desired partial vacuum to each actuator. The changeover valves and pressure converters are activated by the DDE control unit. On activation, a solenoid valve switches the partial vacuum from the vacuum supply to each actuator.
Changeover valves and pressure converters differ with regard to function as follows:
- Changeover valve: Switches the partial vacuum either fully off or on. There are no increments between ambient pressure and maximum partial vacuum.
If a changeover valve is not activated, it is sealed to the vacuum supply side.

- Pressure converter: Can be set steplessly between ambient pressure and maximum partial vacuum.
If a pressure converter is not activated, its is not sealed to the vacuum supply side. A pressure converter causes the vacuum system to lose around 10 mbar per second.











The changeover valves and pressure converters must be checked for the following faults:
- electrical fault
The coil of the solenoid valve and the connections to the plug can have breaks or short circuits.

- Jamming solenoid valve
The solenoid valve can become difficult to move, causing it to jam from time to time. Diagnosing a jamming solenoid valve is a problem, as the jamming often only occurs sporadically. The information under which conditions an actuator does not work must be taken into account.

- Defective vacuum connections
The connections for the vacuum hoses can be broken or burned.







Partial-vacuum canisters
Vacuum is applied to the partial-vacuum canisters by the changeover valves and pressure converters. The partial-vacuum canister contain membranes that are moved by the partial vacuum. The linkage attached to the membranes is connected to the actuators in each case and operates these.
The partial-vacuum canisters must be checked for the following faults:
- No transmission of force between membrane and linkage:
Pull the linkage out of the partial-vacuum canister slightly. If the linkage can be pulled out without resistance, the partial-vacuum canister is defective.

- Membrane is leaking
Use a vacuum pump to apply 500 mbar of partial vacuum to a partial-vacuum canister. If the partial-vacuum canister does not maintain the partial vacuum, the partial-vacuum canister is defective.

Vacuum reservoir
During operation, the vacuum reservoir ensures a certain stored supply of partial vacuum.
The vacuum reservoir must be checked for the following faults:
- Leak-tightness:
Check the leak-tightness of the vacuum reservoir by applying a partial vacuum.

- Leaking connections
The O-rings of the connections can be defective and thus cause leaks.