Parasitic draw (quiescent current)
Definition
Parasitic draw is the current the vehicle consumes with everything switched off and locked; a healthy modern car settles to 20-50 mA once all modules have gone to sleep, which can take 20-60 minutes after locking. A draw above that flattens the battery over days and is caused by a module that fails to sleep (infotainment, telematics, BCM, gateway), a relay stuck on, a glovebox or boot lamp that stays lit, an aftermarket alarm or dashcam, a leaking alternator diode, or a stuck switch on a seat or door. Measure with an ammeter in series with the battery negative or, better, a clamp meter on the negative cable so the car is not woken up by disconnecting power; then wait for sleep and pull fuses one at a time (or measure the millivolt drop across each fuse) until the current falls, identifying the circuit. Do not open doors or use the key during the test, since that wakes the network and resets the sleep timer. Related codes: U-codes for modules that stay awake (U0100, U0140, U0146), B-codes for stuck switches, P0562 (low system voltage), manufacturer codes for a defective bus sleep request.