Component Testing

NOTE: For this test, it is advisable to use the Mercedes-Benz "socket box". This is a special tool available directly from Mercedes-Benz, or through specialty tool dealers. If you do not have access to a "socket box", the numbers given also correspond to the terminal numbers on the specific components being tested.
1. Connect socket box to the CIS-E control unit (control unit connected).
2. With the ignition turned on, check the voltage between sockets 7(-) and 18(+), of the socket box.
a. Reading should be 4.6-5.1 VDC.
b. If voltage is incorrect, replace the control unit.
3. Check the voltage between sockets 7(-) and 11(+).
Altitude (barometric press. (mbar))=voltage
0 meters (1013 mbar) = 4 ± 1 VDC
1000 meters (899 mbar) = 3 ± 1 VDC
2000 meters (795 mbar) = 2 ± 1 VDC
4. If the voltage is not within specification, turn off ignition and check the wiring for continuity. All circuits should show less than 1 Ohm resistance.
a. Socket 7 of the socket box, and terminal 3 of the altitude compensator plug.
b. Socket 18 of the socket box, and terminal 2 of the altitude compensator plug.
c. Socket 11 of the socket box, and terminal 1 of the altitude compensator plug.
5. Start the engine and run at idle speed, and at proper operating temp. (80°C). Check on-off ratio.
a. If the needle oscillates, then all systems are operating properly.
b. If the needle shows a fixed 80%, then replace the altitude compensator.
c. If the needle shows a different fixed on-off ratio, then see TROUBLESHOOTING BY ON-OFF RATIO for further diagnosis.