Function of the injection system: - ra07146020010x(0010)

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N. Electronic idle speed control (ELR) Engine 602.96, 603.96/97 TURBO (Model 463.3: pay attention to variations)

N. Electronic idle speed control (ELR)

Function

The starter ring gear speed sensor (L3) detects the engine speed (144 pulses/ revolution) and passes these in the form of an alternating voltage to the electronic idle speed control unit (N8) or to the ELR/ARA control unit (N8/1).

This processes the speed signal and performs a set/actual value comparison. Idling speed is maintained at a constant level by the actuator (Y22) irrespective of engine load.

Set idling speed is raised in accordance with a specified characteristic curve by the temperature sensor (B11/1) at coolant temperatures <60°C.

Fig 1: Electronic Idle Speed Control Block Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

System diagnostics

Engine 602

The ELR system can be tested by means of the self-test routine integrated in the control unit. A signal can be retrieved with the test connector (X92 or X11/4), which provides concrete information regarding a component fault. The number of signals indicates whether and which component is faulty, or whether the components in the control loop are faulty.

Engine 603

Engine 603 is fitted with a control unit with diagnostics as of 05/88. Control unit designation: RO2 (was RO1).

Pulse readout

Component

All functions "in order"

Engine speed signal "fault"

Coolant temperature "fault"

ELR control loop "fault" ⁽¹⁾

⁽¹⁾	Only short-circuit faults are detected on control units with the designation "RO1". Control units with "RO2" also detect interrupt.

Location of components

Fig 2: Identifying Electronic Idle Speed Control Components Location

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.