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Hunting down a mystery draw on the 10 amp circuit of a 2018 urban g/s

2546 Views 52 Replies 15 Participants Last post by  BlitzSchnell
2018 urban g/s with 20k miles.

I ride daily and noticed a pattern where every 2 or 3 weeks the starter is sluggish and the battery voltage low. Bike may or may not start.

I get the following sequence on 2 batteries, the original and a replacement, both are AGM, lead-acid, load tested and solid.

I have added some electrical things like running lights, phone charger, and all are disconnected before I run the following sequence.

Morning, bike not started since previous day, fuel pump disconnected, tank up, multimeter gator clamps directly on battery terminals. Terminals clean, connections tight. Voltage reads 12.87. Insert key, turn ignition on, do not touch starter button. Voltage instantly drops to 12.4 as I hear the fuel pump cycle, I hear the exhaust flapper servo cycle, and then silence, in the headlamp the 5 watt running bulb is on, otherwise, nothing on, may be the rear brake LED running light, silence. Voltage continues to drop, 12.3. At this point the starter if fired will feel sluggish or may not turn over at all. On occasion I have seen voltage plummet to 11 and 10.3. Then I turn key to off and remove it. Voltage remains constant at say 12.4 or 12.3 and continues dropping until, at exactly 1 minute from when I turn the key to off, I hear and feel a relay in the flapper servo open, a split second later the main relay opens, and instantly, the voltage jumps a 10th of volt, to say 12.5, and keeps on rising steadily back too 12.7 or 12.8.

I pull the 4 amp fuse and the draw persists. I pull the 10 amp fuse and it stops. So seems to be on the 10amp circuit.

I remove the silencer and observe the servo move the flapper normally. Disconnect the flapper servo and turn the key to on, the draw persists. The main relay tested fine, but I replace it, and the draw persists.

I disconnect the fuel pump on the underside the of the tank, and the draw persists.

I disconnect ABS module. Draw persists.

I run the GS-911 and get no faults, all green. I have run the tests in the scanner including those on the flapper servo, fuel pump, and passed all tests.

Does anyone else find the same 1 minute shutdown sequence?

Does anyone know more about what is going on in this sequence and what might be able to cause a strong silent draw?

I have more experience with marine electric, and in those cases, when I saw similar voltage drop on the battery bank it was something like a bilge pump drawing near 10 amps or maybe a momentary drop by a refridgerator compressor firing.

I suspect this draw is maybe 6-8 amps.. it it was over 10 amps it would blow the 10 amp fuse, but that's never happened.

Thanks for reading.

Any ideas appreciated.


Today after posting I began to disconnect components one by one. Disconnect, turn on key, watch for voltage drop, turn off key, observe voltage, reconnect. After about 5 cycles of running this sequence, that is to say, disconnecting 5 components, the voltage drop goes down into the 10 volts.. then 1 minute after key off, you hear the clicks of the 2 relays, and within 1 minute the voltage is back up to 12.6 volts. But at this point, I connect the 2amp noco charger and let the battery top off before I continue testing. So far none of the components I disconnect results in any change in the voltage dip. I do not know every component I have disconnected, but I have taken a pic of each and marked the connector with a white grease pencil. I could work to identify each one, but my plan is to wait until I see the voltage drop stop, at which point I will identify.

Here are the components I am familiar with that when disconnected that have no affect on the voltage drop:

  • exhaust flapper servo
  • fuel pump
  • ABS module

Attached is the wiring diagram from my Haynes manual.


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@IanHoots thanks on the alternator diode. As for drawing constantly, this draw does seem to be constant, it only stops when the main relay opens the circuit. I have not disconnected the alternator yet.

Yes when I pull the 10amp fuse, the draw is not there, which is why I am pretty sure the problem is on that circuit. As for starting with the 10amp fuse out, it cant because the starter is on that circuit.

As for the idle actuator drawing that amount of current itself, I dont think so.. but I am disconnecting components one by one just to try an isolate the problem. My guess is that it is a short, bare copper wire on frame, that is causing a draw this strong, that doesn't make any sound. But that guess is mostly because thats what I have seen on my bikes before. I have thought about shooting around with this thermometer gun looking for high temps.. but really hoping that disconnecting something is going to isolate it to a single component and its wiring.
That's what I'm thinking: keep the, well rested bike in a stable, cool temperature environment and spend some time with a laser temperature sensor.
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