The controller is the central device of the engine management system.
It receives information from the sensors and controls the actuators, ensuring optimum engine operation at a given level of vehicle performance.
The controller is located in the passenger footwell and is secured to the front panel.
Controller marking: ME17.9.71 2123-1411020-50 from BOSCH.
The controller controls the actuators, such as the fuel injectors, the electrically driven throttle body, the ignition coil, the oxygen sensor heater, the canister purge valve and various relays.
The controller controls the switching on and off of the main relay (ignition relay), through which the supply voltage from the battery is supplied to the system elements (except the electric fuel pump, the electric fan, the control unit and the APS status indicator).
The controller switches on the main relay when the ignition is switched on.
When the ignition is switched off, the controller delays the switching off of the main relay for the time necessary to prepare for the next switch-on (completion of calculations, setting of the throttle valve to the position preceding engine start).
When the ignition is switched on, the controller, in addition to performing the functions mentioned above, exchanges information with the APS, if the immobilisation function is enabled.
If, as a result of the exchange, it is determined that access to the vehicle is permitted, the controller continues to perform the engine management functions.
Otherwise, engine operation is blocked.
The controller also performs the system diagnostics function.
It determines the presence of faults in the system elements, switches on the warning lamp and stores in its memory codes designating the nature of the fault and helping the mechanic to carry out the repair.
The controller is a complex electronic device, the repair of which must be carried out only at the manufacturing plant.
During the operation and maintenance of the vehicle, dismantling of the controller is prohibited.
Unauthorised modification of the controller software may lead to deterioration of the engine's operating characteristics and even to its breakdown.
In this case, the vehicle manufacturer's warranty obligations for maintenance and repair of the engine and the management system are lost.
The controller supplies various devices with a supply voltage of 5 or 12 V.
In some cases, it is supplied through controller resistors having such a high nominal resistance that, when a test lamp is connected to the circuit, it does not light up.
In most cases, an ordinary voltmeter with low internal resistance does not give accurate readings.
To monitor the voltage of the controller output signals, a digital voltmeter with an internal resistance of at least 10 MΩ is required.
Controller memory
The controller has three types of memory: programmable read-only memory (PROM), random-access memory (RAM) and electrically erasable programmable read-only memory (EEPROM).
Programmable read-only memory (PROM)
The PROM stores the control program, which contains the sequence of operating commands and calibration information.
The calibration information represents control data for injection, ignition, idle speed, etc., which in turn depend on the vehicle mass, the engine type and power, the transmission gear ratios and other factors.
This memory is non-volatile, i.e. its contents are retained when the power is switched off.
Random-access memory (RAM)
The random-access memory is used by the microprocessor for temporary storage of the measured parameters, calculation results and fault codes.
The microprocessor can, as necessary, write data to the RAM or read it.
This memory is volatile.
When the power supply is interrupted (disconnection of the battery or disconnection of the wiring harness from the controller), the diagnostic fault codes and calculation data contained in the RAM are erased.
Electrically erasable programmable read-only memory (EEPROM)
The EEPROM is used to store the identifiers of the controller, the engine and the vehicle, as well as the password codes of the vehicle anti-theft system (APS).
The password codes received by the controller from the APS control unit are compared with those stored in the EEPROM and are changed by the microprocessor according to a certain law.
The EEPROM is non-volatile memory, its contents are retained when the power is switched off.
Replacing the controller
Important! To prevent damage to the controller when disconnecting the wire from the «minus» terminal of the battery or the wiring harness from the controller, the ignition must be switched off.
Removing the controller
- Switch off the ignition.
- Disconnect the negative battery terminal.
- Unscrew the controller fastening nuts and remove the controller, disconnecting the wiring harness connectors from it.
Note: Disconnect the connectors from the controller only with the controller removed.
In the event of a controller fault, a «new» controller must be used for replacement.
Installing the controller
- Connect the wiring harness connectors to the controller.
- Install the controller on the vehicle.
- Connect the wire to the «minus» terminal of the battery.
Checking the controller's operability
After replacing the controller or resetting the controller using a diagnostic device (mode «5 — Additional tests; 1 — ECU reset with initialisation»), it is necessary to perform the throttle zero adaptation procedure and the misfire diagnostics function adaptation procedure.
Throttle zero adaptation procedure:
On a stationary vehicle, it is necessary to switch on the ignition, wait 30 s, switch off the ignition, wait for the main relay to switch off.
The adaptation will be interrupted if:
- the engine is cranked;
- the vehicle is moving;
- the accelerator pedal is pressed;
- the engine temperature is below 5 °C or above 100 °C;
- the ambient temperature is below 5 °C.
Misfire diagnostics function adaptation procedure:
- warm up the engine to operating temperature (controlled parameter TMOT_W = 60…90 °C);
- accelerate the vehicle in 2nd gear until increased crankshaft speeds are reached (NMOT_W = 4000 min-1) and perform engine braking (NMOT_W = 1000 min-1);
- perform engine braking six times during one trip.
Carry out diagnostics.
