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

2574 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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It might be a chafed/pinched wire?
Do you ride off road with it? (Something knocked out of place, something damaged etc)
DIY service? (Similar to above)
I dont ride off road.. have been inspecting for something like that. With my previous bmw f650's I had a similar problem and the cause was a wire under the tank that was vibrating against the frame and had worn off the plastic coating to the point where it was shorting against the frame. But these bikes were much older. When I look around this bike, everything looks brand new. When I wire up something new, I always wrap the wire in braided or use wire loom. But like I said, anything I have done is disconnected while I am troubleshooting.
Is the bike used daily or every two to three weeks? It sounds like a cycle might not complete when you finish riding possibly. What’s the 10amp circuit for ? It’s a trial and error fix I think.
The only thing connected to the 10A circuit with the key turned off is the electronic control module. and afterwards, everything else controlled by and connected to the ecu. The key energizes the ECU and the ECU is holding the main relay closed on its own, probably through software. One minute may be how long it's programmed to stay on. I don't know. Try disconnecting the other items connected to the ECU. I'd start with the ABS module. I assume your voltmeter is reading the battery directly?
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@Tigcraft "I ride daily"

@gene_apodaca I disconnect ABS model, and draw persists. Yes, tank up, volt meter gator clips directly on the battery terminals. Terminals clean and connection tight. Thanks will add this detail to the initial post.
Is/are the battery/ies lead/acid or the light weight kind ?
@rich46 Good question. Both batteries are AGM, that is to say, absorbed glass mat, lead acid. I will add this detail up top.
I suggest you keep disconnecting stuff from the ECU. Wait. Battery voltage stays in the 12v range until you hit the starter button? It only plummets when you try to start the bike? Once you let go of the starter button, the voltage goes back up the 12v and up? What year is the bike and how many miles are on it?
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@gene_apodaca Thanks. All I do is insert the key and turn on. I do not hit the starter button. The voltage dips as you can hear the fuel pump and the flapper servo cycle.. then voltage keeps dropping. Turn off and remove key, voltage continues to drop until the 1 minute mark when the main relay opens.. then voltage spikes and gradually rises back up. 2018, 20k miles
I suggest you keep disconnecting stuff from the ECU. Wait. Battery voltage stays in the 12v range until you hit the starter button? It only plummets when you try to start the bike? Once you let go of the starter button, the voltage goes back up the 12v and up? What year is the bike and how many miles are on it?
With your battery the problem is something other than the battery (IMHO) FYI in general all the super lite ones tend to have a high voltage spike within 30 to 60 seconds of turning the ignition switch on. We have a battery sponsor and our rep calls this the warm-up time. LOL I know it does sound counter intuitive but even my multimeter shows the voltage rise. Good luck with your problem; I'll go back to work on the vintage racers where there is very few circuits to worry about. With all the interlocking circuits; ECU's and ECM's I'll head to someone whom is conversant this tech.............still I'll bet they can't balance a set of carbs by ear. CHEERS !
@rich46 thanks for the info on the voltage spike. that's interesting.
But, does the voltage drop below 12v without you touching anything other than turning the key on?
Hi Winston, considering the unloaded battery voltage is 12.87, for AGM that is a good charge,
the voltage collapse to 12.3 ignition on and just over 10 v cranking is borderline,
testing the battery cca performance which should be at the rated amps, with a good electronic tester,
and starter motor current draw would be first checks,
the 60 seconds is the network shutdown period and not necessarily an issue,
if it had an overnight drain you would not have the 12.87v
The boxer engine does demand a strong battery, and starter motor,
@gene_apodaca Yes. Not on the first try, but as I wrote, on the 5th try, the voltagae drops into the 10.x volts.

@Forest yes, 12.8x battery after resting all night is proper. Of course, after riding for a while at 14.5v, the batteries will show 13.x right after cut off.
But regarding your point about cranking, at NO point in this exercise I posted am I cranking, starting, turning over the engine. I insert the key and turn it on. Then turn key off. That's it. I do not hit the starter button.
That's telling me that with known good batteries, and the starter is either slow to turn or not turning at all, you should get the starter checked. The other voltage drops and climbs are normal because there's a fair bit of stuff going on with the ECU and various lights. It seems the starter relay is working because the voltage is dropping significantly when you engage the starter.
@gene_apodaca Thank you, but there is a serious misunderstanding. I am NOT touching the start button. I am NOT engaging the starter.
Got it. No attempts at starting the bike and voltage will steadily drop down as low as 10v with no intervention from you at all. The wiring diagram above shows the components controlled by the 10A fuse. The two idle actuators, the ABS module, starter relay, fuel pump and flapper valve, for a total of 6. The starter relay isn't likely the problem because it's working and you replaced the main relay. If you disconnected ALL the others, then try the handlebar connections. It seems really unlikely, but one could be stuck. You could check them with an ohm meter, or disconnect under power as the others. The only component I see that can draw heavy current is the fuel pump and you already tried it. Do you have the ability to isolate individual wires? Pulling them out of the connectors? Because now, I think you're looking for a bad handlebar switch which probably isn't drawing that kind of current, a wire rubbing metal somewhere, or the ECU itself. If you aren't sure you got the idle actuators, try disconnecting the small connector from the ECU and you'll get them both. How long from key on till volts drop below 12V?
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@gene_apodaca thank you. I will check tmrw and make sure I've checked the idle actuators and post back. Thanks for the brain power.
It's unfortunate that it only does the problem ever couple of weeks, I would be sniffing around the diodes in the alternator (metaphorically). That is not typical current draw for a faulty alternator diode, they usually draw constantly when faulty.

Have you tried pulling the 10 amp fuse when it plays up? Will it still crank to allow you to test?
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