BMW E61 Leakage Current

Issue

This BMW E61 5-Series Touring (pre-facelift) frequently ran out of battery power. The display kept showing “increased battery discharge.” The owner had replaced the ULF/MULF module (phone module) himself. He suspected this was the cause. We explained that if you replace a module, you need to learn/program it. If you don’t, you might experience malfunctions. We also indicated that it’s likely the leakage current is coming from somewhere else, but that learning it is a good first step.

Working method

We started by scanning the 5 Series from start to finish using BMW ISTA. ISTA is the original software also used by BMW dealers. We saw over 25 error codes. Then we performed a leakage current measurement. The quiescent current was over 0.3 A (300 mA). That’s far too high. 0.1 A is the limit and actually quite high.

First, we properly learned the new ULF module. This ensured it wasn’t causing any problems. Despite the learning process, the quiescent current remained far too high.
We then inspected the interior. We found aftermarket wiring and an old AV system. In consultation with the customer, we removed this. The quiescent current decreased, but it wasn’t yet satisfactory.

With additional measurements, we found a short circuit in the Comfort Access module. We see this frequently. The cause is often water coming into contact with the antenna/receiver of the keyless system. This can cause a short circuit.

Result

The quiescent current is now below 0.1 A and therefore within specification. The car returns to sleep mode, the battery maintains charge, and the “increased battery discharge” message disappears. Upon scanning, there are no more error codes requiring immediate attention. The owner can once again drive their 5 Series without worry.