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50/55- Road Speed signal input from the Instrument Cluster-G22-W/BL-signal - also goes to Automatic Climate Control Head Channel 17 - which you can read out speed as well, the Servotronic Control Module, the cruise control module and the UrS4 lockable rear differential controller (under the rear seat so it can dis-engage the rear diff lock at 15 mph (25 kph)). More details about the white/blue wire and where its branches go is available HERE. More info about the G22 Vehicle Speed Sensor (VSS) 012409191D . The ECU uses this road speed signal to know that the vehicle is moving so that when throttle position switch (Pin 52/55) is indicating closed but the vehicle is moving, the ECU can shut down the injectors to save fuel while coasting. Conversely, if the road speed is zero and throttle is closed, the ECU knows that this is the idle condition and it keeps the injectors active.

52/55 - Signal from F60 Idle Switch -V/V- a microswitch inside the G69 throttle potentiometer that tells the ECU that the throttle is closed. With this signal and the Road speed signal on Pin 50/55, the ECU knows that the car is either idling at a stop or coasting throttle closed and decides how to handle the injectors accordingly.

• AAN Motronic ECU device list and T55 connector pin-outs from the FAQ