What Causes Volkswagen Electrical Leakage?
2 Answers
The causes of electrical leakage include issues with the vehicle's alternator, main relay, etc. Electrical leakage in a car refers to the phenomenon where the battery gradually discharges while the vehicle is parked, leading to difficulties in starting the car or malfunctioning electrical equipment. Specific reasons: The primary cause is insufficient power generation from the vehicle's alternator, meaning the alternator is faulty. Particularly during rainy nights when more electrical devices are in use, the battery may also lose charge. Prolonged undercharging can significantly reduce the battery's storage capacity, resulting in the inability to start the car the next day. If the car occasionally fails to start and checks on the alternator and the vehicle's static current show no issues, it is advisable to inspect the contacts of the "main relay" in the main control system for any signs of sticking. This issue is often subtle and may not be detected after replacing the battery or starting the car. Alternatively, replacing the main relay might help. Some cars may suddenly lose battery power the next day, making it impossible to start. This is mainly due to electrical devices operating in the circuit, such as trunk lighting or other devices not controlled by the ignition switch that continue to consume power. Batteries that have been in use for a long time, some for three or four years, may still function. Although the battery's capacity might seem sufficient, the shedding of active material inside the battery can fill the slots, creating a circuit between the positive and negative plates and causing discharge. Frequent driving on bumpy roads can also lead to premature shedding of active material, resulting in the same issue. Methods to address undercharging: Among various car maintenance issues, undercharging (electrical leakage) is a very common problem. Generally, for carburetor cars (with fewer electronic control modules and power-consuming components), the natural discharge over about two weeks should not significantly affect starting (the battery itself has some self-discharge). For electronically controlled cars (with more electronic control modules and power-consuming components), not starting for about a week may affect normal starting. If the time frame is shorter than this, it indicates a fault or a problem with the battery itself. Apart from normal power loss, another scenario is difficulty starting after leaving the car unused for a few days following nighttime use. If there is no electrical leakage, the car's charging system should be checked. Sometimes, loose connections in the charging circuit can prevent the battery from being fully charged, leading to a semi-discharged state during peak power usage (such as summer nights). Over time, this can mimic electrical leakage. Methods to detect electrical leakage in cars: When a vehicle is hard to start, measuring the starting current to assess the battery's condition is one of the primary diagnostic steps. To measure, adjust the meter's range to "40A/200A," open the clamp, and place the meter head around the positive terminal cable of the battery. Another person assists by starting the engine. At the moment of starting, the technician operating the clamp meter presses the DH button to hold the data. Since starting the engine and pressing the DH button are performed by two people and may not be synchronized, multiple measurements may be necessary. As the starting current is instantaneous, the DH button's data-holding function is particularly important here.
Last week, my Volkswagen Tiguan suddenly wouldn't start. The mechanic checked for a long time and found it was a parasitic drain issue. For older cars like ours, the most common cause is worn-out wiring harnesses in the trunk area, especially for models with frequently opened trunks. Also, faulty door lock sensors can be really troublesome - the car thinks it's not locked and keeps draining power. Owners who've installed aftermarket infotainment screens should be extra careful, as poorly installed low-quality equipment with improper wiring causes the most severe power drains. The most dangerous scenario is when wiring under the steering wheel gets worn by floor mats and causes a short circuit - this absolutely requires regular inspection. Now I always use a multimeter to check for dark current after parking - anything over 50mA definitely indicates a problem!
