The CAN bus enables rapid data exchange between the following control units:
The DDE control unit sends the following information via the CAN bus:
The other control units send the following information to the DDE control unit:
From this information, the DDE control unit calculates the corresponding engine torque values for ASC or AGS interventions and returns this data to the two other control units.
The DDE control unit controls the preheating/DDE indicator via a line to the instrument cluster in the following form:
The preheating time depends on the engine temperature. It is approx. 4 seconds at an engine coolant temperature of 20 o C to 60 o C. Preheating does not take place at temperatures above 60 o C.
In addition to indicating preheating, the preheating/DDE indicator is also activated in the event of serious faults in the system (fault codes 1, 3, 5, 21 or 47) as long as the fault is currently applicable.
The DDE control unit sends the engine speed signal (tD-signal) and the fuel consumption signal (ti-signal) via two lines to the instrument cluster.
The cut-in and cut-out phases of the A/C compressor are controlled by the DDE control unit.
For this purpose, the control unit receives the request to switch on the A/C compressor via a line from the A/C switch in the heating operating unit and via a line from the air conditioner control unit.
The DDE control unit switches on the A/C compressor under the following conditions:
The A/C compressor is switched off at full load (when driving off or accelerating).
In addition, the A/C compressor is not switched on when the following faults are currently applicable:
The engine can only be started when the DDE control unit receives a valid enable code from the immobilizer (EWS) control unit. The DDE and EWS control unit are mutually linked by the enable code.
After replacing the DDE control unit it is not operable before it has been calibrated together with the EWS control unit in the vehicle. This EWS/DDE calibration takes place automatically after variant encoding with the programming program.
This calibration procedure can also be carried out with the diagnostic program (service functions).
The fault code 45 is stored if the EWS/DDE calibration is not carried out or not correctly.
The actuator sensor is located in the distributor-type injection pump and supplies the DDE control unit with the current position of the fuel volume actuator for controlling the injection volume.
The actuator sensor is a contactless inductive generator.
Fault code 21 is stored if the sensor is defective. In addition, the fuel feed to the distributor-type injection pump is interrupted by the electrical shut-off valve.
The hot-film air mass meter records the air mass drawn in by the engine.
The exhaust gas recirculation and the injected volume are controlled dependent on this factor.
Fault code 38 is stored if the hot-film air mass meter is defective.
The needle movement sensor (or start of injection sensor or permanent injection nozzle) is located on the fuel injection nozzle of cylinder No. 4.
This sensor determines the start of injection of the injection nozzle.
In addition, the engine speed is calculated from this data and is compared with the value of the engine speed sensor. This enables fault monitoring of the needle movement sensor. Fault code 5 is stored if the sensor is defective.
The engine speed transmitter is installed on the engine flywheel. It sends the DDE control unit signals for calculating the engine speed.
In order to monitor the transmitter for faults, the engine speed value is compared with the engine speed value which is derived from the signal provided by the needle movement sensor. Fault code 47 is stored in the case of fault.
The pedal position sensor is a potentiometer which registers the position of the accelerator pedal and signals it to the DDE control unit.
An idle switch is additionally provided for detecting the idle position.
Fault code 37 is stored if the pedal position sensor is defective.
The temperature sensor is installed in the cylinder head and registers the engine coolant temperature.
The temperature of the engine coolant influences the fuel injection quantity control, the start of injection control, the exhaust gas recirculation control and the preheating time control.
In order to avoid engine damage, the full load injection quantity is reduced as from an engine coolant temperature of 107 o C.
Fault code 53 is stored if the temperature sensor is defective.
In this case, the engine is protected from overheating only by the engine oil temperature sensor.
Test note:The temperature sensor is irreparably damaged by a short to U-batt (battery voltage).
The temperature sensor is installed on the oil filter and registers the temperature of the engine oil.
Separate acquisition of the engine coolant and engine oil temperatures enables extended overheating protection for the engine.
The full load injection quantity is reduced as of an engine oil temperature of 130 o C.
Fault code 36 is stored if the temperature sensor is defective.
In this case, the engine is protected from overheating only by the engine coolant temperature sensor.
Test note:The temperature sensor is irreparably damaged by a short to U-batt (battery voltage).
The fuel temperature sensor is installed in the distributor-type injection pump and registers the temperature of the fuel.
The temperature of the fuel influences the injection quantity control.
Fault code 35 is stored if the temperature sensor is defective.
Test note:The temperature sensor is irreparably damaged by a short to U-batt (battery voltage).
The boost pressure sensor registers the absolute pressure (boost pressure and atmospheric pressure together) in the intake system and serves the sole purpose of protecting the engine from excessively high or excessively low boost pressure.
Fault code 54 is stored if the boost pressure sensor is defective and the injection quantity is reduced.
Fault code 101 is stored if the boost pressure deviates too far from its setpoint at engine speeds above 3000 rpm and the engine output is also reduced in this case.
The glow plugs are powered via the glow plug relay. The relay is switched by the DDE control unit and is protected by an 80 A fuse link.
The heating phase consists of preheating, start standby heating and post-heating.
The preheating time depends on the engine coolant temperature and the battery voltage, and is indicated by the preheating/DDE indicator.
It is approx. 4 seconds at an engine coolant temperature of 20 o C to 60 o C. Preheating does not take place at temperatures above 60 o C.
Start standby heating takes place for 10 seconds in ignition lock position 2. After the engine has started, post-heating takes place for approx. 5 seconds in order to improve the idle and exhaust gas characteristics.
If there is a fault in the heating time control, the DDE control unit receives an error signal from the glow plug relay and fault code 8 is stored.
The electric shut-off valve is installed in the distributor-type injection pump. It interrupts the fuel supply when instructed to do so by the DDE control unit.
Fault code 3 is stored in the case of fault.
Two damping-controlled engine mounts prevent engine vibrations being transmitted to the body and thus improve idling comfort.
The system consists of two engine mounts and an electric changeover valve which is activated by the DDE control unit. The electric changeover valve is additionally connected via two pressure lines to the brake booster and the vacuum pump.
Damping of the engine mounts is controlled by the electric changeover valve. The engine mounts are set to soft (active) when idling, otherwise they are set to hard.
The presupply pump is located in the fuel tank. It is activated via a relay and delivers the fuel via the fuel filter to the distributor-type injection pump.
A shutter system is mounted on the radiator in order to dampen engine noise.
The system consists of a radiator shutter, a vacuum cell, the radiator shutter temperature switch, the E-box temperature switch and an electric changeover valve which is activated by the DDE control unit. The electric changeover valve is additionally connected via two pressure lines to the brake booster and the vacuum pump.
The shutter is opened when the engine coolant temperature or the temperature in the E-box exceeds a certain value.
The injection quantity is controlled under all operating conditions on the basis of following variables:
The injection quantity (volume) is set in the distributor-type injection pump by means of the control slide valve (volume control) in the fuel quantity actuator. The actuator sensor signals the actual position of the control slide valve back to the DDE control unit.
Fault code 1 is stored if the actual position determined by the actuator sensor deviates too far from the actual position calculated in the DDE control unit. For safety reasons, the fuel supply to the distributor-type injection pump is then interrupted by means of the electric shut-off valve.
The injection quantity (volume) is limited:
The injection quantity (volume) is increased:
The maximum injection quantity (volume) is limited to a substitute value of 33 mg/stroke (corresponds approximately to a maximum speed of 190 km/h at full load) if the following faults are currently applicable:
A substitute value of 21 mg/stroke is still used for the DDE 2.2 control unit with the part numbers 2246541 and 2246616 (installed up to 5/96). This value further limits the maximum speed to approx. 140 km/h).
The start of injection is controlled under all operating conditions on the basis of following variables:
The start of injection is set in the distributor-type injection pump by means of the solenoid valve for the injection timing device. The actual start of injection is signalled back to the DDE control unit via the needle movement sensor (start of injection sensor, continuous injection nozzle) on the fuel injection nozzle of cylinder No. 4.
Fault code 10 is stored if the actual value determined by the needle movement sensor deviates too far from the setpoint calculated in the DDE control unit. If this fault is currently applicable, the maximum injection quantity is limited to a substitute value of 33 mg/stroke (corresponding to a maximum speed of 190 km/h at full load).
A substitute value of 21 mg/stroke is still used for the DDE 2.2 control unit with the part numbers 2246541 and 2246616 (installed up to 5/96). This value further limits the maximum speed to approx. 140 km/h).
Instead of start of injection control, the system is controlled on the basis of fixed timing of the solenoid valve when
The exhaust gas recirculation is controlled under all operating conditions on the basis of following variables:
Exhaust gas is returned via the exhaust gas recirculation valve (EGR valve) into the intake tract depending on the air mass measured by the hot-film air mass meter. This reduces pollutant emission (nitrogen oxide component) of the engine.
The exhaust gas recirculation valve (which opens from 5 to 85 %) is controlled by means of a variable vacuum which is produced by an electropneumatic pressure converter.
The necessary vacuum is produced by a vacuum pump and mixed with atmospheric pressure.
Exhaust gas recirculation is switched off when:
The exhaust gas recirculation function is also switched off when the following faults are currently applicable:
A constant speed can be set with the aid of the cruise control function without having to press the accelerator pedal.
The cruise control must be switched on or off with the main switch in order to avoid incorrect operation via the multifunction steering wheel.
The cruise control (FRG) standby indicator lights when the cruise control is switched on.
The cruise control is operated by means of buttons in the multifunction steering wheel.
The ASC control unit signals the current vehicle speed via a separate line to the DDE control unit.
Fault code 29 is stored if the speed is not recognized.
The cruise control is switched off when:
A switch is installed on the clutch pedal to detect clutch operation. This switch is not fitted on vehicles with automatic transmission.
The DDE control unit evaluates the signals from the brake light switch and brake light test switch in order to record brake operation.
The test switch makes it possible to monitor the brake light switch. Fault code 26 is stored in the case of fault.
Cruise control cannot be activated or is switched off when one of the following faults is currently applicable: