Why can't you directly connect the negative terminal when jump-starting a car with auto start-stop?
2 Answers
Cars equipped with auto start-stop function should not have the negative terminal directly connected during jump-starting, as it may cause program disturbances and affect the vehicle's operation. Therefore, when jump-starting, avoid connecting directly to the battery's negative terminal; instead, secure it to any metal part of the car body. Below are relevant details: Features of start-stop technology: Basic start-stop technology automatically shuts off the engine when the car encounters a red light or traffic jam, and the engine promptly restarts when the driver releases the brake pedal or presses the clutch (or accelerator pedal). More advanced start-stop systems also include brake energy recovery, converting some of the braking energy into electrical energy to recharge the battery. Function of engine start-stop: Used during low-speed driving and frequent stops, it automatically turns off the engine to avoid unnecessary fuel consumption and reduce idle time. Less idle time means reduced engine carbon buildup, benefiting both environmental protection and the engine's lifespan.
I've seen many automatic start-stop cars having major issues when jump-starting by directly connecting to the negative terminal. Since these vehicles are equipped with start-stop systems, their batteries are usually AGM type with built-in intelligent modules monitoring voltage and temperature. If you directly connect to the negative terminal, a single cable contact could produce sparks, risking ignition of accumulated hydrogen gas in the battery – that's dangerous. Even worse, those sparks might interfere with onboard computers like the ECU, causing start-stop function failure or permanent damage. The correct method is to connect the positive terminal properly during jump-starting and attach the negative cable to a metal part of the car body near the engine as grounding. This allows current to flow smoothly and is much safer. Regularly check your battery lifespan when driving, and it's best to have it professionally tested at a shop to avoid roadside breakdowns.