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

2548 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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I measured my 2018 UGS so you have some references, note my bike hasn't been run for about week and is not on a trickle charger.

Key Off 0.0A 12.8v
Key On 2.9A 12.4v
After 3mins 2.8A 12.3v
Key Off 2.1A 12.4v
After 60sec 0.0A 12.6v

I can repeat this several times with very little voltage loss... my battery gets back up 12.8v after a few minutes of no load.

It does seem like you have you have something drawing substantial current from the battery when the key is on, if it is getting down to 10v. You need to actually measure the current to know what is really happening.

Page 7.40 of the Haynes manual should guide you to what components are effected when the 10A fuse is pulled. You can rule out the starter motor and alternator as they are connected to the battery even when the key is off.
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