600SEL (140.057) V12-6.0L (120.980) (1993)
Deceleration Shut-off Function
During deceleration, some or all the fuel injectors are turned off (in all gears) if engine temperature is above 70 °C (158 °F). The engine speeds for
injection cut-off/ restart are shown in the chart.
Maximum Engine RPM Function
At excess RPM the fuel injectors are turned off to keep the engine from overrevving. The momentary engine RPM limit is 6200 ±50. After 5
seconds, the LH control units limits the engine to 6000 ±50 RPM. Below 44 km/h (28 mph) the engine speed is limited to 5100 RPM.
Self Adjusting Function
The ECUs are adaptive to the changing engine operating parameters (wear and contamination of parts). They will adjust the calculations according
to assimilated input. Whenever the vehicle is started or driven, the ECUs will use the values they have learned from the previous driving period.
Self Adjusting Oxygen sensor Function
The oxygen sensors (G3/3 and G3/4) operate in a similar fashion. They sense if the fuel mixture is rich or lean and the ECU adjusts the oxygen
sensor control accordingly. This self-regulating function keeps the air/fuel mixture at a constant midpoint. Therefore, the need to adjust CO
content is eliminated and no more possible.
Safety Fuel Shut-off function
If due to a malfunction, the throttle valve opens further than the position called for by the accelerator pedal (cruise control not in operation), The
LH control units receive a signal and go into a "limp home mode." This pre-programmed mode will set the fuel injection frequency (opening
duration) so the engine can't exceed 1300 RPM and the vehicle can be slowly driven to the repair shop.
Diagnostic Function
If an LH control unit detects a specific fault more than 4 sequential times (ignition switch turned ON and OFF), a fault code is stored in the control
unit memory. Only malfunctions which prevent/severely influence starting or operating of the fuel injection system are immediately stored in the
fault memory.
A "CHECK ENGINE" light will inform the operator of an emission related problem. It illuminates when a certain malfunction in the engine
management system is detected. The operator should bring the vehicle to the repair shop as soon as possible.
The malfunction memory can be accessed via the diagnostic connector (X11/4). The malfunction memory is not erased when disconnecting the
battery.
Air Injection Control (AIS)
In order for the catalytic converter to reach operating temperature as soon as possible, air from an air pump (125) is injected into the exhaust gas directly
behind the exhaust valves. The electronic clutch of the air injection is engaged by the LH control unit (N3/3) via the air injection relay (K17). At the
same time, the air injection pump switch-over valve is energized which applies vacuum to the air injection shut-off valve (126).
Air injection occurs after starting the engine at a coolant temperature between 10 °C (50 °F) and 44 °C (111 °F), an engine speed of less than 2750 RPM
and below a specified air mass. The air is injected for a maximum of 155 seconds depending on coolant temperature. The oxygen sensor control in
inactive during air injection.
Camshaft Timing Control
To improve the torque characteristics of the engine, the intake camshafts are "advanced" depending on engine speed and load.
The LH control units operate the camshaft timing adjuster solenoids (one per camshaft). When the solenoids (Y49/1 and Y49/2) are energized, the
camshafts advance. In "P" or "N" the adjustment is dependent on engine RPM only.
Engine speed:
Adjustment:
Up to 2000 RPM
Retarded
From 2000 - 4400 RPM
Advanced
From 4400 RPM
Retarded
Above 250 km/h (155 mph)
Advanced
Selector in "P" or "N"
up to 2500 RPM
Retarded
Selector in "P" or "N"
from 2500 RPM
Advanced
Charcoal Canister Purging Control (EVAP)
The fuel vapors stored in the charcoal canister are purged at temperatures above 70 °C (158 °F) via the purge switch-over valves (Y58/2 and Y58/3).
The vapors then get burned in the combustion process. In order to control the purge quantity, the LH control units activate the switch-over valves at a
frequency of 7.5 Hz (cycles). The purge quantity is determined by the duration of each cycle.