BMW E60 battery drains overnight – measuring quiescent current
E60 battery drains overnight – why does the car not go to sleep?
The car should fall asleep about 30 minutes after being switched off. If some device keeps it awake, the battery drains. Typical causes are the tailgate wiring harness or switch, the seat control units, the Webasto, a bus short circuit and a faulty IBS battery sensor.
How is the E60 quiescent current measured and what is the permitted limit?
Connect an ammeter between the battery negative terminal and ground, or use a clamp meter. Wait for the car to fall asleep (up to an hour). The current should drop to about 0.1–0.02 A. The IBS gives a fault code if the quiescent current exceeds 80 mA.
How do I find the device that is drawing current?
Measure the quiescent current and pull fuses one at a time. When the current collapses, you have found the guilty circuit. Fuses 27 (interior lights and body module), 29 (airbag/diagnostics) and 34 (radio) are the usual suspects. After that, disconnect the devices on that circuit one at a time.
How can I tell whether the car is asleep?
On an automatic, the LED of the P marking on the gear selector stays lit if the car is not asleep. On a manual, the glovebox light stays on. A clicking sound from the engine bay can also indicate that the car keeps waking up.