Mercedes-Benz ML320. Service manual — part 193

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me

Fig. 135: Shift From 1st To 2nd, Function (Second Gear Engaged)
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Aim

Engage front multiple-disc clutch (K1), disengage front multiple-disc brake (B1).

Operation

1st Gear Engaged

The end face of the 1-2/4-5 command valve (31a) is kept depressurized via the 1-2 and 4-5 shift solenoid valve
(Y3/6y3). Via the 1-2/4-5 holding pressure shift valve (28a), working pressure (p-A) is applied to the front
multiple-disc clutch (K1) is depressurized. See Fig. 133.

Shift Phase

Via the 1-2 and 4-5 shift solenoid valve (Y3/6y3), the shift valve pressure (p-SV) is directed onto the end face
of the command valve 1-2/4-5 (31a). See Fig. 134. The 1-2/4-5 command valve (31a) is displaced and the shift
pressure (p-S) coming from the 1-2/4-5 shift pressure shift valve (29a) via the 1-2/4-5 command valve (31a) is
directed to the front multiple-disc clutch (K1). At the same time the front multiple-disc brake (B1) is subjected
to overlap pressure from the 1-2/4-5 overlap regulating valve (30a).

The B1 pressure acting on the end face of the 1-2/4-5 shift pressure shift valve (29a) is superseded by the
working pressure (p-A). The increasing shift pressure (p-S) at the front multiple-disc clutch (K1) acts on the
annular area of the 1-2/4-5 overlap regulating valve (30a). With an appropriate pressure level at the 1-2/4-5
holding pressure shift valve (28a) this valve switches over.

2nd Gear Engaged

After the gear change is complete, the pressure on the end face of the 12-/4-5 command valve (31a) is reduced
via the 1-2 and 4-5 shift solenoid valve (Y3/6y3) and the command value is pushed back into its original
position. See Fig. 135. Via the 1-2/4-5 holding pressure shift valve (28a) working pressure (p-A) now reaches
the front multiple-disc clutch (K1) via the 1-2/4-5 command valve (31a).

The front multiple-disc brake (B1) is disengaged (depressurized). The spring in the 1-2/4-5 shift pressure shift
valve (29a) pushes this into its original position.

Operating Pressure, Function

See OPERATING PRESSURE, FUNCTION.

Shift Pressure, Function

See SHIFT PRESSURE, FUNCTION.

Modulating Pressure, Function

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me

See MODULATING PRESSURE, FUNCTION.

Shift Valve Pressure, Function

See SHIFT VALVE PRESSURE, FUNCTION.

Lubricating Pressure, Function

See LUBRICATING PRESSURE, FUNCTION.

Regulating Valve Pressure, Function

See REGULATING VALVE PRESSURE, FUNCTION.

Limp-Home Mode, Function

Operation

In order to ensure a safe driving state and to prevent damage to the automatic transmission, the ECT control
module (N15/3) switches to limp-home mode in the event of critical faults. A fault code assigned to the fault is
stored in memory.

All solenoid and regulating valves are thus de-energized.

Effect



The gear last engaged remains engaged.



The modulating pressure and shift pressure rise to the maximum levels.



The torque converter lockup clutch is switched off.

In order to preserve the operability of the vehicle to some extent, the hydraulic control can be used to engage
2nd gear or reverse:



Stop Vehicle



Switch Off Engine



Move Selector Lever To "P"



Wait At Least 10 Seconds



Start Engine



Move Selector Lever To "D": 2Nd Gear



Move Selector Lever To "R"

The limp-home function remains active until the fault is rectified or the stored fault code is erased. Sporadic
faults can be reset via ignition OFF/ON.

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me

Upshift/Downshift Solenoid Valve, Location/Design/Task/Function

See UPSHIFT/DOWNSHIFT SOLENOID VALVE, LOCATION/TASK/DESIGN/FUNCTION.

Location/Task/Design/Function Of PWM Solenoid Valve, Torque Converter Lockup Clutch

See LOCATION/TASK/DESIGN/FUNCTION OF PWM SOLENOID VALVE, TORQUE
CONVERTER LOCKUP CLUTCH.

Modulating Pressure Regulating Solenoid Valve, Location/Task/Design/Function

See MODULATING PRESSURE REGULATING SOLENOID VALVE,
LOCATION/TASK/DESIGN/FUNCTION.

Shift Pressure Regulating Solenoid Valve, Location/Task/Design/Function

See SHIFT PRESSURE REGULATING SOLENOID VALVE,
LOCATION/TASK/DESIGN/FUNCTION.

Operating Pressure, Function

The working pressure supplies pressure to the hydraulic control and transmission elements. The working
pressure is the highest hydraulic pressure in the entire hydraulic system. The working pressure is regulated at
the working pressure regulating valve in relation to the load and gear. All other pressures required for
transmission control are diverted from the working pressure.

Working Pressure Regulating Valve, Location/Task/Function

See WORKING PRESSURE REGULATING VALVE, LOCATION/TASK/FUNCTION.

Upshift/Downshift Solenoid Valve, Location/Task/Design/Function

See UPSHIFT/DOWNSHIFT SOLENOID VALVE, LOCATION/TASK/DESIGN/FUNCTION.

Shift Pressure Control Solenoid Valve, Location/Task/Design/Function

See SHIFT PRESSURE REGULATING SOLENOID VALVE,
LOCATION/TASK/DESIGN/FUNCTION.

Multiple-Disc Brake, Location/Task/Design/Function

See MULTIPLE-DISC BRAKE, LOCATION/TASK/DESIGN/FUNCTION.

Multiplate Clutch, Location/Task/Design/Function

See MULTI-PLATE CLUTCH, LOCATION/TASK/DESIGN/FUNCTION.

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me