What is the KL15 line?
1 Answers
KL15 represents the engine ignition signal (corresponding to the IGN state of the car key), and also indicates the signal for turning the key to start the car. Most ECUs require the car to be in the started state to operate, such as the ECUs of the chassis system, ABS, ESP, ABM, etc. KL15R (R stands for Radio) is when the key is turned to the position where the radio works (corresponding to the ACC state of the car key), but the car has not yet started, for example, the dashboard and windows receive this signal. This signal is powered by the ZentraleElektrik (the main electrical box in the car), and is connected to the KL15 pins of each ECU through a fuse. KL30 is the ECU power supply (i.e., connected to the car battery), providing the operating voltage for the ECU, generally between 11V and 15V. Some ECUs can operate when the car is turned off (corresponding to the OFF state of the car key), such as the Body Control Module (BCM). KL31 is the ECU ground source. The KL31 signal is connected to the common ground terminal of the car, usually marked with a W, such as W4 indicating the ground terminal of the engine shield. There are usually several common ground terminals in a car, located near the engine, dashboard, undercarriage, roof, and rear compartment, used for ECU common grounding to maintain consistent ground voltage.
