What is the Principle of Engine Start-Stop?

[Kenneth]

Here is an introduction to the principle and function of automatic start-stop: 1. When the vehicle stops moving due to traffic congestion or at an intersection, the driver presses the brake pedal and shifts to neutral. 2. At this time, the Start/Stop system automatically detects that the engine is idling and not in gear, the wheel speed sensor of the anti-lock system shows zero, and the electronic battery sensor indicates there is enough energy for the next start. 3. When these three conditions are met, the engine automatically stops running. Here are more details about automatic start-stop: (1) Temporary stops during vehicle movement, such as when waiting at a red light. (2) While driving, simply pressing the brake pedal will cause the engine to automatically shut off approximately two seconds after the vehicle comes to a complete stop. Keeping the brake pedal pressed will maintain the engine in the off state. (3) Releasing the brake or turning the steering wheel will automatically restart the engine, allowing immediate acceleration. The entire process remains in the D (Drive) gear state.

[VanSpencer]

I previously studied this start-stop system in detail when getting my car repaired at a 4S shop. At its core, it relies on the vehicle's computer to automatically control engine shutdown and restart. When you brake at a red light, the car senses the stationary state and cuts fuel supply to shut off the engine. During this time, the alternator keeps working, so the AC and audio system continue operating normally. The moment you release the brake pedal, the system immediately sends a signal to restart the engine - the entire process completes within 0.5 seconds without needing to touch the key. This system places high demands on the starter motor and requires an enhanced battery. Once I helped a car owner install an auxiliary battery specifically to protect the main battery. Of course, when the engine is cold and coolant temperature is insufficient, the system won't activate to avoid damaging the engine.

[StCaleb]

Last week, my neighbor's kid asked me why the start-stop function saves fuel. I used his toy car as an analogy: It's like when you release the button on a remote-controlled car, the car stops moving but the battery still drains. A car idling for an hour can waste two liters of fuel for nothing—it's pure waste when the engine runs at a red light. The start-stop technology uses sensors to detect your brake pedal action and sends commands to the integrated starter-generator via the control module. It employs a reinforced starter motor that can endure 200,000 start cycles without failing. When I modified my old car, I added a supercapacitor to protect the circuit. Remember to turn off this function when driving through puddles on rainy days to prevent sudden engine shutdown and water intake.

[AdalineLee]

Having driven a taxi for ten years, I know this system best. Every time the auto start-stop light comes on during traffic jams, the engine goes silent. The system determines whether to stop based on wheel speed sensors and brake signals. It only activates when the transmission is in D gear and the brake is fully pressed. The core relies on an enhanced AGM battery for power—a regular battery would fail within six months. Interestingly, you can't hear the engine restart from outside, but the steering wheel vibrates slightly. In summer, when the AC is on, the stop duration shortens to prevent cabin temperature fluctuations. Remember to clean throttle carbon deposits regularly; otherwise, the system may misjudge.

[Stanley]

Last time at the car club meetup, we discussed whether auto start-stop harms the engine. I shared insights from my engineer friend: It relies on the crankshaft position sensor to confirm the stop state, then the ECU controls fuel injection and ignition timing. When the engine shuts off, the water pump continues circulating via belt drive, so overheating isn't a concern. The key is the optimized starter gear set that reduces meshing impact. Some people modify circuits to disable auto start-stop, but this actually increases fuel consumption by 10%. During the break-in period for new cars, it's recommended to keep it active so the computer can learn driving habits. Note: For frequent short trips, it's better to turn it off to prevent deep battery discharge.