Starter actuation function

W15.30-1026-79

0 Ignition OFF

1 Circuit 15R ON

2 Circuit 15 ON

3 Circuit. 50

4 Engine CAN bus

5 Vehicle CAN bus

A3 Vehicle engine control (FMR) control unit

A6 MR/PLD control unit

A22 PSM control unit

M1 Starter

S1 Drive switch

* Vehicles with
code (ED5) Parameterizable special model (PSM),
code (EM7) Parameterizable special model with body CAN bus or code
(EM8) Parameterizable special module with body and trailer CAN bus

S10 Engine start pushbutton switch

S11 Engine stop pushbutton switch

S103 Cargo lift gate switch
Only vehicles with cargo lift gate

Z1 CAN star point cab dash support
Model 375.3, 950, 952, 953, 954

Z1.1 CAN star point cab dash support
Models 375.1, 970, 972, 974, 975, 976

General information

The starter (M1) is actuated exclusively via the terminal 50 output of the MR/PLD control unit (A6).

This allows the starter (M1) to be protected against mechanical and thermal overloading (start time limitation, overspeed limiting device) and, with the aid of Star Diagnosis, performing active diagnosis by means of a compression comparison measurement.

 The fact that the starter output stage in the MR/PLD control unit (A6) does not deliver sufficient current or is not designed for high currents (the starter output stage switches off for a current of a max. of 3 A at 0°C or 2 A at 25°C) means that there is a front-end relay located between the control unit and the starter solenoid for the starter (M1).

Actuation of the starter (M1) takes place:

 if the terminal 50 signal from the drive switch (S1) is detected at the input of the MR/PLD control unit (A6)

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 if the PSM control unit (A22) - issues a start command, provided that the vehicle is equipped with code (ED5) Parameterizable special module (PSM), code (EM7) Parameterizable special module with body CAN bus or code (EM8) Parameterizable special module with body and trailer CAN bus

 if the Start engine pushbutton switch (S10) is pressed

 if the engine start pushbutton switch (S10) and the Stop engine button pushbutton switch (S11) - are pressed simultaneously - whereby, in this case, the unit pump solenoid valves are not actuated and, as a result, no injection takes place

 The starter (M1) is also activated when no valid transponder code has been recognized in the MR/PLD control unit (A6) for safety reasons.

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Requirements

 Voltage supply (terminal 30 and terminal 15) available at MR/PLD control unit (A6)

 Lock removed from starter function, which means:

 Transmission in neutral (generally required for vehicles with an automatic transmission - for all other vehicles only required for a start demand via the Start engine pushbutton switch (S10), since a start demand must be achieved via the drive switch (S1) under all operating conditions)

 Power take-off or power take-offs deactivated (if fitted)

 Engine stopped or the engine speed is <50 rpm

 Conditions for removing the lock on the starter function are checked by the drive control (FR) control unit (A3). When all conditions have been fulfilled, it will send an appropriate start-enable message to the MR/PLD control unit (A6) via the engine CAN bus (4); the MR/PLD control unit then actuates the starter (M1).

W26.19-1055-80

Determination of the "transmission in neutral" condition

on vehicles with mechanical or hydraulic gearshift
- Sown on transmission 715.050

A3 Vehicle engine control (FMR) control unit

S7 Reverse gear switch

S9 Neutral position switch

For vehicles with a mechanical or hydraulic gearshift determination of gear position is performed directly by the drive control (FR) control unit (A3).

To do this there is, on the one hand, reverse gear switch (S7) and, on the other hand, the neutral position switch (S9) on the transmission. Both switches are directly connected to the drive control (FR) control unit (A3) whereby the switching conditions of the neutral position switch (S9) are the most important factor for determining the neutral position of transmission.

W26.21-1060-80

Determination of the "transmission in neutral" condition

On vehicles with code (GE1) Automatic gear control (AGS)

A3 Vehicle engine control (FMR) control unit

A92 Automatic gear control (AGS) hydraulic controller unit

B60 Gear sensor (SGG)

B61 Gate sensor (SGE)

CAN 5 Transmission CAN

On vehicles with code (GE1) Automatic gear control (AGS), the drive control (FR) control unit (A3) receives the information on the gear position from the automatic gear control (AGS) controller unit (A92). The automatic gear control (AGS) control unit is located in the controller unit and recognizes the transmission positions on the basis of the information from the gear sensor (SGG) (B60) and gate sensor (SGE) (B61), converts these to corresponding messages and transfers them to the drive control (FR) control unit (A3) via the transmission CAN (CAN 5).

W26.20-1196-80

Determination of the "transmission in neutral" condition

On vehicles with code (GS2) Gear control
- Shown on transmission 715.5

5 Vehicle CAN bus

A3 Vehicle engine control (FMR) control unit

A16 GS/EPS control unit

B60 Gear sensor (SGG)

B61 Gate sensor (SGE)

Z1 CAN star point cab dash support

Z2 Additional cab dash support CAN star point

On vehicles with code (GS2) gear control, the drive control (FR) control unit (A3) receives information concerning the transmission position from the GS/EPS control unit (A16).

The GS/EPS control unit (A16) detects transmission positions on the basis of the information from the gear sensor (SGG) (B60) and the gate sensor (SGE) (B61), converts this information into appropriate messages and then sends these messages to the drive control (FR) control unit (A3) via the vehicle CAN bus (5).

W27.19-1096-80

Determination of the "transmission in neutral" condition

On vehicles with transmission 723.6 (automatic transmission)

A3 Vehicle engine control (FMR) control unit

A49 Allison automatic transmission control unit

K57 Allison neutral relay

For vehicles with transmission 723.6 (automatic transmission), the drive control (FR) control unit (A3) recognizes the neutral position of the transmission via the switching position of the Allison neutral relay (K57) which is actuated by the Allison automatic transmission control unit (A49).

W26.45-1273-76

Determination of the "Power take-off or power take-offs deactivated" condition (if applicable)

5 Vehicle CAN bus

A3 Vehicle engine control (FMR) control unit

A22 PSM control unit

P2 Instrument
- up to 31.12.1999

P4 Instrument cluster 2000
- As of 01.01.2000

S23 PTO 1 indicator switch

S64 PTO 1 switch

S65 PTO 2 switch

S66 Power take-off 3 switch

S79 PTO 2 indicator switch

S80 PTO 3 indicator switch

S108 Switch, ADR

Y46 PTO 1 solenoid valve

Y47 PTO 2 solenoid valve

Y48 PTO 3 solenoid valve

Z1 CAN star point cab dash support
Model 375.3, 950, 952, 953, 954

Z1.1 CAN star point cab dash support
Models 375.1, 970, 972, 974, 975, 976

** Vehicles without
code (ED5) Parameterizable special model (PSM),
code (EM7) Parameterizable special model with body CAN bus or code
(EM8) Parameterizable special module with body and trailer CAN bus

* Vehicles with
code (ED5) Parameterizable special model (PSM),
code (EM7) Parameterizable special model with body CAN bus or code (
EM8) Parameterizable special module with body and trailer CAN bus

The operating status of the power take-off or power take-offs (depending on vehicle equipment) is transmitted either by the PSM control unit (A22) or instrument (P2) or instrument cluster 2000 (P4), depending on the construction period, and travels via the vehicle CAN bus (5) and CAN star point cab dash support (Z1 or Z1.1, depending on model) to the drive control (FR) control unit (A3).

Determination of the operating state is accomplished on the basis of the switch positions of the indicator switches for PTO 1 (S23), PTO 2 (S79) and PTO 3 (S80), connected either to the PSM control unit (A22) or the instrument (INS) (P2) or instrument cluster 2000 (P4), depending on the equipment.

i.e., the switch positions of the power take-off 2 (S79) and power take-off 3 (S80) indicator switches are only recorded by the PSM control unit (A22) and the switch positions of the power take-off 1 (S23) indicator switch can, depending on the vehicle equipment, either be recorded by the PSM control unit (A22) or by the instrument (P2) or instrument cluster 2000 (P4).

W30.35-1097-81

Determination of the "engine stopped/
engine speed <50 rpm" condition

4 Engine CAN bus

A3 Vehicle engine control (FMR) control unit

A6 MR/PLD control unit

B15 Crankshaft angle position sensor

B16 Cylinder TDC sensor

The engine speed, as determined by the MR/PLD control unit (A6) passes via the engine CAN bus (4) to the drive control (FR) control unit (A3).
From the drive control (FR) control unit (A3), it is transferred, on the one hand, via the vehicle CAN bus (5) to the instrument (P2) or instrument cluster 2000 (P4) and, on the other, used for checking the prerequisites and therefore, the associated start enable.

Function sequences

1 Actuation of the starter (M1) in the case of a start command from the drive switch (S1)

 The terminal 50 signal line will be interrupted on vehicles with a cargo lift gate
as soon as the cargo lift gate switch (S103) is actuated. In order to achieve actuation of the starter (M1) the cargo liftgate switch (S103) must be in the starting position.

On switching on the ignition (terminal 15) and turning the ignition key to the engine start position (position terminal 50 (3)), the terminal 50 signal from the drive switch (S1) is passed on simultaneously to the drive control (FR) control unit (A3) and the MR/PLD control unit (A6).
The drive control (FR) control unit (A3) sends a message concerning the start command to the MR/PLD control unit (A6) via the engine CAN bus (4) just as soon as the terminal 50 signal is applied to the control unit input which compares this with the directly arriving terminal 50 signal from the drive switch (S1) (consistency testing).

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If the circuit 50 signal is applied to the MR/PLD control unit (A6), without the message being transmitted by the drive control control unit (FR) (A3), then after 1 s the fault "circuit 50 inconsistent" is stored in the fault memory and the start is delayed by this time. If, for example, the CAN bus system fails, this redundancy will allow the vehicle to be started via terminal 50 and driven to the next workshop at a predetermined engine speed, provided that a correct transponder code is recognized.
If the MR/PLD control unit (A6) receives the terminal 50 signal simultaneously via the terminal 50 connection at the control unit input and via the engine CAN bus (4), the control unit actuates the starter (M1) immediately (without delay).

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The starter (M1) continues to be actuated until the start command is retracted, the engine has reached the starter break-off speed (approx. 450 rpm for a warm engine and up to approx. 650 rpm for a cold engine) or the maximum start time of 90 s has been exceeded (start time limitation).

 If a compression comparison measurement is made with the aid of the STAR DIAGNOSIS, the MR/PLD control unit (A6) will also interrupt actuation of the starter (M1) after a specific period of time.
The compression comparison measurement is based on the fact that the piston for a cylinder with the poorer compression passes by the ignition TDC more rapidly than a cylinder with good compression.
There can also, exactly at this moment, be slight rpm fluctuations

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which the MR/PLD control unit (A6) can detect based on the rpm signals of the crankshaft angle position sensor (B15) and the cylinder 1 top dead center sensor (B16). It calculates the deviations between the individual cylinders and sends these to the Star Diagnosis where they are displayed in % comparative values. Firing of the engine is prevented in that the solenoid valves in the unit pumps are not actuated in order to obtain the most accurate possible values for the compression comparison measurement.

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2 Actuation of the starter (M1) for a start request from PSM control unit (A22)

 (ED5) Only for vehicles with code (EM7) Parameterizable special module with body CAN bus or code (EM8) Parameterizable special module with body and trailer CAN bus.

The PSM control unit (A22) is networked via the vehicle CAN bus (5) with the drive control (FR) control unit (A3). Once an appropriate message concerning the start command has been sent by the PSM, the drive control (FR) control unit (A3) checks for fulfillment of the conditions and, if fulfilled, passes on the start command together with the start release with appropriate messages to the MR/PLD control unit (A6).

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The MR/PLD control unit (A6) actuates the starter (M1) until the start command from the PSM control unit (A22) is retracted, the starter break-off speed has been reached (about 450 r.p.m. for a warm engine up to about 650 r.p.m. for a cold engine) or actuation of the starter (M1) is interrupted to protect against mechanical or thermal overloading (start time limitation).

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3 Actuation of the starter (M1) in response to a start command from the Start engine pushbutton switch (S10)
The switch positions of the Start engine pushbutton switch (S10) are analyzed by the MR/PLD control unit (A6). Once the Start engine pushbutton switch (S10) has been pressed, the engine control (MR) control unit (A6) sends a message via the engine CAN bus (4) concerning the start command to the drive control (FR) control unit (A3).
The drive control (FR) control unit (A3) checks for acceptability, that is the conditions which must be fulfilled to remove the lock on the starter function, and releases the start if all conditions are fulfilled through sending an appropriate message.
On receiving the message, the MR/PLD control unit (A6) actuates the starter (M1) until the Start engine pushbutton switch (S10) is released again, the starter break-off speed has been reached (about 450 r.p.m. for a warm engine up to about 650 r.p.m. for a cold engine) or actuation of the starter is automatically interrupted to protect against mechanical or thermal overloading (start time limitation).

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4 Actuation of the starter (M1) in the case of simultaneous actuation of the engine start pushbutton switch (S10) and engine stop button pushbutton switch (S11)

 This functionality is used to turn the engine for doing service work without it starting.

As soon as the MR/PLD control unit (A6) detects that the engine start pushbutton switch (S10) and engine stop button pushbutton switch (S11) are being pressed simultaneously, it actuates the starter (M1) but interrupts actuation of the solenoid valves in the unit pumps.
This prevents fuel injection and the engine the engine will therefore not fire.

Actuation of the starter (M1) again only occurs if all conditions have been fulfilled and the drive control (FR) control unit (A3) issues the start release.

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 The signal which initiated a start must always be retracted again for safety reasons before a new start is possible based on the same signal (start locking).

If the starter (M1) was actuated by pressing the Start engine pushbutton switch (S10) or by simultaneous pressing of the Start engine pushbutton switch (S10) and Stop engine pushbutton switch (S11) then starting the engine using the drive switch (S1) is for safety reasons only possible after the ignition has been switched off and then on again.