General Information
Windshield Wiping/Washing
The windshield wiper/washer system on the E38 is similar in operation to previous ZKE systems. The wiper/washer system consists of the GM III, wiper switch, two relays, the wiper motor, the washer pump and the headlight washer pump I module.
All wiping/washing functions are controlled from the stalk switch. The system has four wiping stages and four interval wiping speeds.
The functions of single wipe, intermittent wipe, slow and fast wipe are coded input signals to the GM III through two circuits. The GM recognizes from the combination of high/low signals which wiping function to activate.
The intermittent wiping time inputs are provided by a potentiometer mounted in the stalk switch.
Single Wipe
Single wipe is activated by depressing the wiper stalk switch down. When depressed momentarily, the wipers will make a single pass across the windshield.
Intermittent Wipe
The wiper intervals are dependent on the road speed signal. The interval time will vary from 26 seconds with no road speed to 2 seconds at high speeds depending on the intermittent setting selected.
A potentiometer, connected to the knurled wheel, on the wiper stalk provides the input for the basic wiping interval. The voltage value of the potentiometer varies from 1.49V to 3.5 V from position one to position four interval wipe.
Slow/Fast
The wiping speed in stage I and stage II are also road speed dependent. Stage I follows the previous logic where stage I switches to intermittent when the vehicle is stopped. Additionally, stage II now switches to stage I when the vehicle is stopped.
To protect the wiper motor from excessive loads, the return contact (parking contact) is used as an input signal for wiper operation. If the return contact signal is not present for 16 seconds, indicating a blocked wiper arm, the wipers will switch off.
The GM III receives the vehicle speed signal over the K-Bus. If the signal is defective or missing, the GM will use the Servotronic input speed "A" signal for operation.