03:03-02

Issue 1

en

Scania DEC2 control system, V7.0

Work description
Diagnostics and fault finding

Part No.
1 588 738

Scania CV AB, Sweden, 2001-02:1

Important information

Changes must not be made to the DEC2 control unit or sensors and wiring. Doing so
may effect the control unit's safety system and cause injuries to the operator and
damage to the engine or driven equipment.
Never splice a damaged cable. Renew the entire cable, otherwise the safety and
operation of the system could be impaired.
The sensors for the DEC2 control system are dedicated for use in DEC2 only.
To avoid damage to the DEC2 control unit, proceed as follows:
Check that cables to the battery and generator are properly connected before the
engine is started.
Before disconnecting the cable to the control unit, switch off all power supply to the
unit.
Disconnect the DEC2 control unit when rapid charging the battery.
Disconnect the battery before arc welding.

Contents
Engine protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Settings for DIP switches in the control unit . . . . . . . . . . . . . . . . . . . . . .4
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Main indicator lamp (operator's lamp) . . . . . . . . . . . . . . . . . . . . . . . . .5
Lamp test/fault code switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Troubleshooting procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Reading fault codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Failure of input signal to speed accelerator/trim interface. . . . . . . . . . . .9
Cable or connection faults to separate inputs . . . . . . . . . . . . . . . . . . . . .9

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Engine protection

Diagnostics

In the control unit it is possible to select

monitoring functions to protect the engine in case
of faults which might cause damage to the engine.
One of these functions reduces the engine power
output to enable the vehicle or boat to be driven
the nearest service workshop.
The control unit is also constantly monitoring
itself to detect faults in its own operation.
If there is a risk that the engine cannot be
controlled in a safe way, it will automatically be
stopped.
All these functions work together to allow
maximum power output, at the same time
reducing the risk of engine damage.

Diagnostic functions are integrated in the control

unit. These functions enable the system to detect a
number of faults.
By way of a diagnostics port, authorized service
personnel may connect a computer (PC) to
investigate the cause of most problems.
The control unit contains a fault memory, where
important information about detected faults is
stored. The fault memory has storage capacity for
48 detected faults. The detected faults are stored
in a non-volatile memory and remain in the
memory even after the voltage supply to the
control unit is interrupted.
The fault log function is available via F6 in the
Tuning screen. Refer to booklet 03:03-03.
Using the fault log, the fault codes may be read,
erased or saved to a separate file.
For each fault, a text description is shown along
with a code text and the operating time when it
occurred.
Note: The COMM/DIAG port is for use by
authorized personnel only.

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Settings for DIP switches in the control unit

There are 8 DIP switches in the control unit

behind the black, round rubber cover.

No.

ON

Default position

Default position

The switches have the following functions in the

ON or OFF positions.

OFF

Default position

Calibration position (injection pump DEC2)

Limited operating power (Power-) with

threshold values for low oil pressure and/or
excessive coolant temperature

Shutdown position (Shutdown) for low oil

pressure and/or excessive coolant
temperature

Fixed speed operation when accelerator input

signal fails (900 rpm + speed droop)

Shutdown when accelerator input signal fails

All speed engine: Default position

Single speed engine: High speed request
(1800 rpm)

Single speed engine: Low speed request

(1500 rpm)

Calculation of no-load speed droop

Calculation of speed droop under load

Speed droop for operation with Map 2

Speed droop for operation with Map 1

- The default position of all DIP switches on

delivery is ON. However, for single speed
engines, switches 6, 7, and 8 are in position
OFF.
- Shutdown at threshold values for low oil
pressure and high coolant temperature can be
selected by setting DIP switch 4 to OFF.
- With DIP switch 4 in position ON, Powerindication is obtained for these threshold
values. Engine power output reduction (LOP)
can then be selected to prevent damage to the
engine. Refer to booklet 03:03-03, Tuning and
calibration.

DIP switches in ON position

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Troubleshooting
Even though the control system provides
sophisticated fault finding, the operator can
determine the cause of problems without test
equipment and take appropriate action.
Any fault that is field correctable will be displayed on the LED display on the control unit
when a fault finding procedure is in progress.
To enable readout of the LED fault indication, a
switch for lamp test/fault code test must be
located near the control unit so that the LEDs can
be observed when the switch is activated.
Main indicator lamp (operator's lamp)
If a fault occurs, the main indicator lamp on the
control panel will come on.
A corresponding lamp is also included in the main
supply box for DEC2 in Scania's electrical
equipment.
If the main indicator lamp on the instrument panel
comes on, the DEC2 control unit has detected a
fault, indicating that a warning threshold has been
reached.
If DIP switch 4 is in position OFF, the engine will
be shut off if the oil pressure is too low or the
coolant temperature too high.

03:03-02

Lamp test/fault code switch

This switch is integral with the main indicator
lamp on the main supply box for DEC2 in
Scania's standard electrical equipment.
If Scania's standard electrical equipment is not
used, it is important to install this switch close to
the DEC2 control unit.
The recommended type of switch is a spring
return switch with - (negative) in the rest position.
Before reading out the faults on the LEDs on the
control unit panel, this switch must be depressed.
The lamp test function will then briefly turn on all
the LEDs and then display the fault code.
Refer to page 6 for the complete fault code read
out procedure.

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Troubleshooting procedure
LED indication during
operation when a fault occurs
Note: Indication is given by the main
indicator lamp on the main supply
box and on the operator's instrument panel. The lamp test/fault
code switch should not be
depressed.
CONTROL STATUS

The LED continous to flash even if a fault

has arisen and this means that the control
unit has power.
POWER-

If the LED comes on, the control unit has

detected a fault condition which could cause
engine damage if allowed to continue.
The control unit automatically reduces
engine power output to a predefined level if
the corresponding function has been
selected.
Action: Reduce engine speed to idle and
conduct trouble-shooting according to
instructions on page 7 and the chart on page
8.
SHUTDOWN

The LED comes on and the engine is

switched off automatically if such a severe
fault has occurred, that it will cause damage
to the engine unless operation is stopped.
Action: Conduct trouble-shooting according
to instructions on page 7 and the chart on
page 8.
If the engine has not stopped, reduce engine
speed to idle and conduct trouble-shooting
as per above.

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Reading fault codes

Note: If the engine has stopped or lost

power but the operator's warning
lamp is out and neither POWERnor SHUTDOWN are on, the fault is
outside the control unit's detecting
range. Probable causes: fuel
shortage, temporary overload,
mechanical fault.
- Depress the lamp test/fault code switch. In
Scania's electrical equipment the main warning
lamp is located in this switch (1) in the main
supply box.
- All LEDs will then come on for 2 seconds to
indicate that they are intact and in working
order. This also applies to the main indicator
lamp in the main supply box and on the
instrument panel. Make a note of any LED that
is defective.
- All LEDs are then put out for approx. 4
seconds.

- The control unit then automatikcally returns to

operating mode
- When you have made a note of the fault code
displayed, the memory for the lamp test/fault
code function is reset by briefly switching off
the power supply with the rotary switch (2).
- The most likely cause of the fault can be found
in the troubleshooting chart on the next page.
- When the fault or faults have been rectified the
engine can be restarted.
- If the control system still indicates a fault
(main warning lamp still on), other faults may
have been recorded. The fault code test must
then be repeated as per above.
- The fault or faults will be stored in a separate
memory in the control unit along with the
operating time when it occurred. Stored faults
can be accessed and erased by authorized
service personnel.

- Next, one of the LEDs will show a fault code

for 2 seconds. Make a note of which LED is
on.

1. Combined main warning lamp and lamp test/fault code switch

2. Rotary switch for main supply to the control unit
3. Stop switch for stopping the engine in the engine compartment
Main supply box

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READING FAULT CODES

POWER+

POWER-

BOOST LIMIT

TORQUE LIMIT

RUNNING

STARTING

SHUTDOWN

CONTROL STATUS

LED INDICATION WHEN THE LAMP TEST/FAULT CODE SWITCH IS ACTIVATED

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= LED is on

Probable cause

Action

DEC2 has detected an internal fault in the control unit.

Send in the control unit for repair as soon as

possible.

The engine temperature has reached the threshold level

or the temperature sensor is inoperative.

Check the cooling system. Check the

temperature sensor and wiring.

The engine has reached the overrevving limit or the

engine speed sensor is inoperative.

Check the wiring and connector.

Renew the engine speed sensor.

Control rack position sensor inoperative.

Check connectors and cables to governor.

The intake air temperature has reached the threshold

level or the charge air temperature sensor is
inoperative.

Check the intake system. Check the temperature

sensor and cable routing.

DEC2 detects no charge air pressure.

The charge air pressure sensor is inoperative.

Check the charge air hose. Send in the control

unit if the connection has been damaged.

Engine speed potentiometer or the idling safety switch

is inoperative.

Check the cable routing, connectors and cables.

Renew the engine speed sensor

The oil pressure has dropped to the threshold level or

the oil pressure monitor is inoperative.

Check oil level, connector and cable.

Renew the oil pressure monitor.

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Failure of input signal to speed

accelerator/trim interface

Cable or connection faults to

separate inputs

- All speed engines with APS (accelerator

position sensor):
If the excitation signal (TPSE) or sensor signal
(TPSS) fails, this sensor failure will result in
the following: The engine speed is first reduced
to idle speed and then increased to a fixed
speed of 900 rpm + speed droop or shutdown
depending on the position of DIP switch 5.
Refer to page 4.
If the return signal (TPSR) fails, the engine
speed may briefly be increased and then
reduced and proceed to the same sequence as
above.
- Single speed engines with trim potentiometer:
If the excitation signal (TPSE) or the sensor
signal (TPSS) fails, the control unit uses full
negative trim (approx. -90 rpm) if the trim
input is enabled with the Speed Hold switch in
Battery- position.
If the return signal (TPSR) fails, the control
unit uses full positive trim (approx. +90 rpm) if
the trim input is enabled with the Speed Hold
switch in Battery- position.

03:03-02

If any of the separate inputs in the control unit

fails or is not connected, automatic internal
switching to Battery- will take place.
This will result in the following function mode for
each of the separate inputs (switches):
Speed droop/isochronous:Speed
(Droop/Isochronous)
droop mode
Power control:
(Power Control)

Power/
torque curve 1

Run/Stop:
(Run/Stop)
stage

Switches off
the control final

Speed Hold:
(Speed Hold)

No speed hold

Lamp test/fault code:

Active mode

Idle/Run:
(Idle/Run)

Idle speed

Note: Cables that are not connected act

as antennae, receiving noise,
cellular phones ringing etc. All
cables must always be connected.

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