New or Modified Output Signals/Components

AUXILIARY FAN CONTROL












Identical in function to the ME 7.2, the Auxiliary Fan motor incorporates an output final stage that activates the fan motor at variable speeds.

The auxiliary fan is controlled by M5.2.1. The motor output stage receives power and ground and activates the motor based on a PWM signal (10 - 100 Hz) received from the ME 7.2.

Similar to the aux fan in the E46 with MS 42.0 control, the fan is activated based on the following factors:

- Radiator outlet temperature sensor input exceeds a preset temperature.
- IHKA signalling via the K and CAN bus based on calculated refrigerant pressures.
- Vehicle speed
- Battery voltage level

When the over-temperature light in the instrument cluster is on (120 °C) the fan is run in the overrun function. This signal is provided to the DME via the CAN bus. When this occurs the fan is run at a frequency of 10 Hz.

SECONDARY AIR INJECTION SYSTEM












The purpose of the secondary air injection system is to provide fresh air to the catalytic converters during the crucial warm-up phase of operation immediately after cold start. This accelerates oxidation of hydrocarbons and brings the catalytic converters to the point of light-off earlier.

The M73 TU secondary air injection system continues to be a two speed system utilizing two relays and a slow speed resistor. The introduction of the SKE M5.2.1 control modules (SOP 5/97) allocated a dedicated control circuit for the vacuum vent valve improving comprehensive component monitoring. This continues with the M73 TU M5.2.1 system.

However, the primary controller of the Secondary Air Injection System has switched for the 1999 model year (M73 TU - M5.2.1)

- DME I activates the vacuum vent valve and Stage I relay simultaneously but separately providing the open air ports through the non return valves and slow air pump speed
- DME II activates the resistor bypass circuit through activation of the stage II relay providing the fast air pump speed if necessary.

All parameters of operation are programmed in the M 5.2.1 control modules and varied by monitored conditions:

- Engine Temp
- Engine Speed
- Engine Load

ELECTRICALLY HEATED THERMOSTAT

OVERVIEW






















Initially introduced on the M62 engine in 1996, model specific variants of the electrically heated thermostat are now equipped on all LEV compliant engines. The M73 TU and M62 TU thermostat housing has a quick connect coupling.

This thermostat allows the engine to run hotter than conventional thermostats improving fuel economy. The DME also electrically activates the thermostat to lower the engine coolant temperatures based on monitored conditions. It is both a conventionally functioning and DME controlled thermostat (two stage operation). DME control adds heat to the wax core causing the thermostat to open earlier than it's mechanical temperature rating providing increased coolant flow.

CONVENTIONAL FUNCTION: The thermostat begins to open at 103 °C. This is at the inlet side of the water pump and represents the temperature of the coolant entering the engine.

Before the 103 °C temperature is realized, the coolant is circulated through the engine block by the water pump.

After the temperature reaches 103 °C it is maintained as the inlet temperature by the thermostat. The coolant temperature at the water pump engine outlet is approximately 110 °C. The additional 7 °C is achieved after the coolant has circulated through the block.

The operating temperature of the engine will remain within this range as long as the engine is running at part load conditions and the engine coolant temperature does not exceed 113 °C.

DME CONTROL







Electric thermostat activation is based on the following parameters:

- Engine temperature > 113 °C
- Radiator Coolant Outlet Temperature
- Load signal "ti" > 5.8 ms
- Intake air temp > 52 °C
- Vehicle speed > 110 MPH

When one or more of these monitored conditions is determined, the DME activates (switched ground) the thermostat circuit. The activated heating element causes the wax core in the thermostat to heat up and open the thermostat increasing coolant circulation through the radiator which brings the engine temperature down.

The temperature of the coolant at the inlet side of the water pump will drop to approximately 85 °C and the temperature at the outlet side will drop to approximately 103 °C when activated.