Control Unit - (CIS-E) On/Off Ratio Test/Impulse Readout
TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERSDate: June 1992
REF.NO.: 07.3/15a
SUBJECT:
ON/OFF Ratio Test And Impulse Readout
Engine 102.985
In order to read the On-Off ratio on Federal version 190E 2.3 models, the CIS-E control unit must be activated as with 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.
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 has come 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 lit until the start button is depressed again for at least 6 seconds.
With the ignition turned on, both CIS-E control units (Federal and California) will display a fixed on-off ratio of 85%
NOTE:
The Output of the CIS-E control unit (N3) performs the two functions of impulse readout and on/off ratio. Following the impulse readout test, the control unit must be reset to the on off ratio test mode by switching the ignition off and on.
If the ignition is not switched off before the engine is started, the control unit remains in the impulse readout mode. In this state, the control unit will provide undefined voltage levels which, in the on/off ratio measuring range, will lead to false readings on lambda control testers and on diagnostic testers with on/off ratio test mode.
The display may, for example, be a constant 0% or 100% on/off ratio, or erratic pointer movements which may easily be interpreted as malfunctions The on/off displays on Bosch and VDO control units are different.
Components which are replaced without regard to this information will be rejected on future warranty claims.