Control Unit - CIS-E, On/Off Ratio Test/Impulse Readout
90mercedes04TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: October 1990 REF. NO.
SUBJECT: MALFUNCTION READOUT AND CHECKING ON-OFF RATIO MODEL 190E 2.3 (201.028) MODEL YEAR 1991
REF. NO. MBNA 07.3/15
In order to read the On-Off ratio on Federal version 190E 2.3 models, the CIS-E control unit must be activated as the model year 1988 and 1991 California version vehicles. This became necessary due to the incorporation of the malfunction memory in the control unit of the Federal version vehicles.
Figure 1:
On-Off ratio readout
Since Federal version vehicles do not have the push button switch and LED lamp in the test connection for diagnosis (X11/4), the impulse counter must be connected as shown in Figure 1.
Push start button for 2.4 seconds. If the number "1" appears on the display, push the start button again for 2-4 seconds. If a number other than "1" appears on the display, perform the appropriate test steps in the Electric Component Test and repair the failure. The on-off ratio can only be checked if no malfunction is stored in the CIS-E control unit.
If the "CHECK ENGINE" lamp came on due to a failure in the O2-sensor circuit, the failure has to be corrected and the failure code "5" must be erased from the memory by depressing the start button for at least 6 seconds. At this point the CHECK ENGINE lamp will still be on until the start button is depressed again for at least 6 seconds and the lamp will go out.
With the ignition turned on, both CIS-E control units (Federal and California) will display a fixed on-off ratio of 85%.