Author Topic: Odd BMW can-bus behaviour - any ideas?  (Read 3088 times)

wimblejon

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Odd BMW can-bus behaviour - any ideas?
« on: July 31, 2023, 05:20:33 PM »
I have an R1200GS (2013) and have just fitted a HEX EZcan II to control, 1) Aux driving lights up front, 2) white emblem lights, 3 & 4) amber left and right turn on the emblem lights. All working fine.

I thought I'd like to add some extra stop/tail lights, so bought a strip of 12v red LEDs, cut it into 2 and fixed them vertically to the side of the number plate (UK, large yellow, at the rear).

As all 4 EZcan outputs were used up, I thought I'd chance tapping them off the bikes lights as spending another lump of money on another EZcan for just one circuit was too much for my wallet to bear!

Initially I wired them in parallel to the wire going in to the OEM rear stop/tail light (+ground) and they worked! I assumed that the small extra amperage wouldn't upset the bike's can bus and indeed they worked, dim on bike ignition, brighter, with the stop light when either brake is applied.

Then they stopped working, as did all the rear lights, with the dash error 'LAMPR !'
When I disconnected my added LED strips the fault goes away.

My question is:
Why did the strips work fine initially and now don't?
Do you know about the BMW GS can bus?
Why is it so upset all of a sudden? :)

Borgia

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Re: Odd BMW can-bus behaviour - any ideas?
« Reply #1 on: July 31, 2023, 06:16:44 PM »
Do the LED strips still work (i.e. did they short out?)?

I have yet to see any specs for the ZFE's (not the CAN-bus - this is a popular misconception) threshold parameters as to when it declares an open circuit or short circuit condition. Perhaps someone on here knows.
Hey BMW: No service manual = no new bike.

wimblejon

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Re: Odd BMW can-bus behaviour - any ideas?
« Reply #2 on: July 31, 2023, 08:11:15 PM »
Hey Borgia,

I did test the strips this morning and they still work fine (on 12v).

I also tested the voltage from the bike's stop/tail light wire (to ground) and on 'normal' rear running lights (the bike, not my strips) I was getting about 1.3 volts and on applying the brake, it went up to 12v and full brightness.

????

Borgia

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Re: Odd BMW can-bus behaviour - any ideas?
« Reply #3 on: July 31, 2023, 08:14:26 PM »
Well that may be normal as the taillight is Pulse Width Modulated (PWM) with the duty cycle being 100% when the brake light is illuminated and something less than 100% when the running light is illuminated. Just as your eye perceives the lower duty cycle as being dimmer a voltmeter would see the pulsed 12V as something less than 12V.
Hey BMW: No service manual = no new bike.

wimblejon

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Re: Odd BMW can-bus behaviour - any ideas?
« Reply #4 on: August 01, 2023, 11:22:23 AM »
Thank you Borgia.
I'm still confused as to why the lights worked fine and then stopped. . . but to ensure that one of the strips hasn't failed and drawing too much current, I'll try connecting a couple of spare strips and see what happens. I'll report back. Thanks.

wimblejon

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Re: Odd BMW can-bus behaviour - any ideas?
« Reply #5 on: August 21, 2023, 07:15:11 PM »
Hi all,
I added a 10ohm resistor in line to the positive (+) feed to the added LED strips and it now works!
Without the resistor, the bike canbus complains, none of the rear lights work and there is a warning on the driver display.
With the resistor, there is no error warning, and the additional LED strips operate with the rear/stop light as 'normal'!
Thank you all for your help.