Self-Study Program

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367_069
367_070
367_032
Electromagnetic valves
In the case of the electromagnetic valves, a
distinction is made between shift solenoids with
two switching positions (OPEN - CLOSE) and
electronic pressure control valves (known as EPCVs
or modulating valves).
The shift solenoids (N88/N89) are so-called 3/2 way
valves or OPEN-CLOSE valves.
3/2 valve means the valves has 3 connections and
2 switching positions (open/closed or
OPEN–CLOSE). These valves are used for switching
hydraulic shift control valves.
The electronic pressure control valves (EPCV)
convert an electrical current to a proportional,
hydraulic control pressure. This control pressure, in
turn, activates hydraulic shift control valves, which
control the "working pressure" of the shift elements,
the lockup clutch and the master pressure.
Two types of EPCV are used.
EPCVs with a rising characteristic increase
pilot pressure (P) as a function of rising control
current (I) - no current - zero pilot pressure
(0 mA = 0 bar).
EPCVs with a falling characteristic reduce pilot
pressure as a function of rising control current
- no current - max. pilot pressure.
EPCV with falling
characteristic
EPCV with rising
characteristic
Effects of malfunctioning:
If the self-diagnostics detect a faulty
electromagnetic valve, the limp-home mode is
normally activated. You will find more information
about the limp-home mode on page 55. Electrical
and mechanical malfunctions have very different
effects due to the complexity of the electro-
hydraulic control system. The effects may be
confined to the actual malfunctioning system
(e.g. in the case of N91, the lockup clutch), but
they can also cause the vehicle to enter limp-home
mode if safe operation is no longer assured.
Examples:
N93 controls the master pressure.
If EPCV N93 fails, the gearbox will operate at
maximum system pressure. The effects are "clunky"
shifting from "P" or "N" to "D/S" or "R" and during
gearshifting in general.
EPCV N91 controls the lockup clutch.
If EPCV N91 fails, the lockup clutch cannot be
activated and therefore remains open.
Shift solenoids
OPEN-CLOSE valves
N93 N90 N92 N283 N282
N88
N89
N91