Does leaving an OBD device plugged into a car for a long time have any impact?
4 Answers
Under normal circumstances, leaving an external OBD device plugged into a car for an extended period does not have significant effects, as the device only reads data from the car's onboard computer via the OBD port and cannot write data. However, faulty external devices may adversely affect the car through the OBD interface, so it is not recommended to keep them plugged in long-term. Function of the OBD port: The OBD diagnostic interface connects to the serial data bus of the onboard computer. All sensors and communication devices on the onboard computer communicate via a single serial bus, and the data is then interpreted by a decoder. For example, data such as coolant temperature, vehicle speed, and fuel tank levels are transmitted by sensors as encoded data over the CAN bus to the onboard computer, which decodes the information. With the appropriate decoder and decoding software, any device connected to the bus system can recognize, send, and read data. Risks of plugging in external OBD devices: If the connected electronic product is substandard—such as drawing excessive power or having poor quality leading to a short circuit—it can damage the OBD port. If the standby current is too high, it may drain the car battery, eventually preventing the vehicle from starting. Therefore, any product connected to the OBD port must be of high quality.
I've left the OBD scanner plugged into my car for over half a year without removing it. This device serves as the vehicle's data port and should automatically power off when the engine is turned off, but some devices may secretly drain power. Especially during summer exposure to intense sunlight, low-quality OBD module casings can easily deform, and poor contact might trigger fault codes on the dashboard. Last month, I returned from a two-week business trip to find my battery drained, and the auto repair shop owner directly pointed to the OBD device not entering sleep mode as the cause. It's advisable to purchase one with a physical switch for peace of mind when parked. Additionally, older cars with aging wiring need extra attention—keeping it plugged in long-term may accelerate port wear, and it can interfere with the ECU during data reading, potentially causing the engine light to come on. It's best to unplug it if the car will be parked for more than five days.
Using an OBD port HUD device for three years, here's my experience. Most devices do enter sleep mode after the engine is off and don't drain the battery, but those with real-time GPS tracking will continuously consume power. My old Passat's battery died prematurely due to long-term GPS tracker usage. Those with modified electrical systems should be extra cautious—a friend's Civic installed a cheap OBD tire pressure monitor that interfered with the auto start-stop system. The OBD socket pins are quite delicate; long-term use with attached modules can cause loosening or oxidation on bumpy roads, and water ingress during rain may lead to short circuits. If you notice delayed engine starts or abnormal window operation, it's likely due to power drain from the OBD device. For short commutes it's fine, but always unplug for long-term parking.
Last time I saw a discussion about this on the forum. The biggest hidden danger of keeping OBD devices plugged in is battery drain, especially for Bluetooth modules, as background communication consumes a lot of power. A colleague's Hyundai Elantra couldn't start because of this. It also easily interferes with the diagnostic equipment at 4S shops—the technician complained during my last maintenance that they couldn't read complete fault codes with a third-party device plugged in. Modified cars are a different story; some car enthusiasts installed OBD ambient lighting, which caused the turn signals to malfunction. In fact, the OBD port wasn't designed for long-term loads when the vehicle was engineered, and the plastic clips are prone to break under prolonged pressure. When choosing a device, check the sleep current parameter—those below 10mA are relatively safe. If your car battery is three years old, it's better not to take the risk.
