Testing the diode matrix - ra54001401433x(1433)

A. Function test, B. Inputs/outputs, C. Diodes of diode matrix, D. Function Model 140 with Engines 119 to 06/92, 120 

Operation no. of operation texts and work units or standard texts and flat rates:

1. Function test 
   Fig 1: Identifying Engine Speed Increase Diode Matrix (Right Footwell)

   Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
   NOTE: The engine speed increase is deactivated at a coolant temperature >110 °C.

   Engine	start.
   Drive position D, 3, 2, or 1	engage, engine speed approx. 550 rpm.
   Heated rear window	switch on.
   Engine speed	increase in drive mode to >1000 rpm.
   Car with drive mode engaged	stop.
   Engine speed	check, specification approx. 650 rpm.
   Further function test	perform with the following electrical loads; first of all switch on the next load then switch off the preceding load. Headlamps (except if daytime headlamp control fitted) Blower stage 3 or higher if automatic heater control fitted Automatic climate control Front seat heaters stage 2 Rear seat heaters stage 2 Specification approx. 650 rpm. If the specified value is not achieved with one or several electrical loads, perform B.
   Selector lever position	engage, specification approx. 550 rpm.
   Engine	switch off.

2. Testing inputs and outputs of diode matrix 

   Preliminary work:

   Function test, A.

   Front passenger footrest removed.

   Right front pillar cover removed (68-150) .

   Fig 2: Wiring Diagram Of Diode Matrix Without Daytime Headlamp Control

   Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

   Wiring diagram of diode matrix without daytime headlamp control (part no. 000 540 32 24) 

   Fig 3: Wiring Diagram Diode Matrix With Daytime Headlamp Control

   Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

   Wiring diagram diode matrix with daytime headlamp control (part no. 000 540 35 24) 

   Connector (5) of diode matrix (V2)	unplug, plug in.
   Ignition starter switch	in position 2, in position 0.
   Electrical load	switch on for which no idle speed increase occurred.
   Voltage at pin for connector 5 output of diode matrix (V2)	measure. Specification: battery voltage. Specification reached: test idle speed control/electronic accelerator as described in Diagnosis Manual. Specification not reached: detach connectors of electrical load concerned (1, 2 or 3) from diode matrix and test voltage at connectors (1, 2 or 3). Specification: battery voltage. Specification not reached: Test control cable, repeat if necessary. Test outlet for control cable at electrical load as described in Diagnosis Manual. If 1. and 2. in order, perform C.

3. Testing diodes of diode matrix 

   Preceding work:

   Test as per B.

   BLOCKING DIRECTION
   
   

   Diodes in diode matrix (V2)	measure by setting multimeter to diode test: terminal (red) to output 5. Terminal (black) in turn to the inputs; see wiring diagrams. NOTE: Pay attention to daytime headlamp wiring diagram.
   	Specification: ∞ Ω.
   	Specification not reached, renew diode matrix (V2).

   CONDUCTING DIRECTION
   
   

   Diodes in diode matrix (V2)

   measure by setting multimeter to diode test: terminal (black) to output 5. Terminal (red) in turn to the inputs; see wiring diagrams. Specification: breakdown voltage approx. 1 V. Specification not reached; renew diode matrix (V2).

   Commercially available testers 

   Multimeter

   e.g. Fluke 23 or 83

4. Function 

Idling speed is increased in certain conditions from 550 rpm to 650 rpm in order to achieve a higher charging current at idle.

The idle speed increase is activated if drive mode D, 3, 2, or 1 is engaged, if engine speed of 630 rpm is exceeded and one or several of the following electrical loads are switched on:

• low beam (except if daytime headlamp control fitted)
• blower stage 3 or higher if automatic heater control fitted
• heated rear window
• automatic climate control
• left and right auxiliary fans
• front or rear heated seats stage 2

The idle speed increase is deactivated if selector lever position P, R or N is engaged and also if coolant temperature rises above 110°C.

The idle speed is increased by the control module which is responsible for idle speed control. The control module is activated by the diode matrix of the electrical loads. The diode matrix prevents reverse currents to the other connected electrical loads if one or several loads are switched on.

Fig 4: Identifying Engine Speed Increase Diode Matrix (Right Footwell)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

V2 Engine speed increase diode matrix (right footwell)