Electronic Throttle Control Module: Description and Operation

Electronic Accelerator System Diagram:

PURPOSE
The electronic accelerator control module (N4/1) controls the cruise control, idle speed functions and electronic engine control (electronic accelerator pedal) for ABS/ASR III to ensure smooth and consistent operation regardless of engine temperature and load.

OPERATION
When the ignition switch is in the ON position, the idle speed control function is in operation. The position of the throttle valve for idle speed and ABS/ASR III is determined by the control module via the nominal value potentiometer (accelerator pedal input) in the electronic accelerator actuator (M16/3, location left). The actual value potentiometer in the electronic accelerator actuator (M16/3) signals the position of the left throttle valve. At the same time, the actual value potentiometer in the electronic accelerator actuator (M16/4, location right) signals the position of the right throttle valve to the control module. The control module compares the signals and specifies the position of the throttle valves via the output signals. This signal is used by the electronic accelerator actuators (M16/3 and M16/4) to adjust the throttle valve.

Before starting the engine, the throttle valve position is determined by the engine temperature. Once the engine is running, the idle speed and ABS/ASR III are controlled by the electronic accelerator control module which provides a constant idle RPM and limits the maximum torque output to the drive wheels. For torque output regulation (ABS/ASR III), the control module uses the input signal from the ABS/ASR control module.

The electronic accelerator control module uses the following information to determine the throttle position:

Input Signals
^ Base module (N16/1)
^ ABS/ASR control module (N30/1)
^ LH control modules (N3/2 and N3/3)
^ EZL/AKR ignition control modules (N1/4 and N1/5)
^ Idle speed contact switch (S29/3)
^ Electronic accelerator actuators (M16/3 or M16/4)
^ Stop lamp switch (S9/1)
^ Starter lockout/backup lamp switch, selector lever position recognition (S16/3)
^ Cruise control switch (S40)
^ A/C compressor engagement signal
^ Data exchange via controller area network (CAN)
^ Wheel speed sensors (L6/1 - L6/4)

Output signals
^ Electronic accelerator actuator (M16/3 and M16/4)
^ ABS/ASR control module (N30/1)
^ LH control modules (N3/2 and N3/3)
^ EZL/AKR ignition control modules (N1/4 and N1/5)
^ Impulse readout (malfunction memory) via 38-pole diagnostic socket (X11/4)
^ Data exchange via controller area network (CAN)

Idle speed control function
The idle speed control function uses the following information to determine the correct idle speed:
^ Engine speed (TN-signal)
^ Coolant temperature
^ Vehicle speed signal
^ Selector lever position
^ Diode matrix signal

Idle Speed/Temperature Chart:

During idle, the control module keeps the engine speed at a constant RPM depending on engine coolant temperature.

Warm-up RPM Graph:

Warm-up Control Function
The warm-up control is effective at all engine temperatures. After each start-up (accelerator pedal in idle position) the engine increases the idle speed for approx 20 seconds. Between 20 °C (68 °F) and 30 °C (86 °F) the engine speed is 800 - 950 RPM.

Maximum Speed Function
The maximum vehicle speed is limited to 250 km/h (155 mph). If this speed is exceeded, the throttle closes slightly to restrict the air intake into the manifold.

A/C engagement Control Function
When the A/C compressor is turned on, the throttle valve opening is increased before the A/C compressor engages. This keeps the engine idle speed at a nearly constant RPM.