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Old 02-28-2013, 10:24 AM   #1
ixab OP
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Question Heated grip voltage WTF

So, here's a good story. In trying the grip swap shown in another thread, I might have damaged the left element. It has a tiny scratch that is suspicious. The left grip stays cold, so that's likely what happened. However, that's not my WTF moment.

As part of diagnosing the lack of heat on that side, threw the multimeter on the wires that are attached to the element. This is where things get cra-cra-crazy. Powered off, I get 0.0 on the meter. Turn the bike power on, I get 7.4 on the meter, regardless of the heated grip switch setting. What? High, low, or off, same reading on the meter, dead on. Keep in mind that the grips should remain off when the bike isn't running. Also keep in mind that a normally operating grip get's 12-13 at full power, and a PWM 12-0-12 at 1/2 power. So, 7.4 makes no sense at all . It gets better. Turn the ignition off, and the 7.4 stays on the meter for about 30 seconds. Wow! So the CANBUS system sends power to that wire even after the bike is switched off? Why?

Luckily I found a left grip used, so I can just replace the whole thing and see if that helps. I'll report back once I get the part.

Another detail. In doing the swap on the right side, I cut through the (+) wire that attaches to the element. I managed to splice it back together, and the right side is working normally. Not sure if that would somehow freak out the left side, but with the magical BMW electrical system, who knows?

As an side rant; how can BMW persist in putting exceptionally crappy grips on the GS, and worse, grips that the user can't swap for something that's much more off road appropriate. If I ever get another GS, I'll skip the factory heated grips. The integrated bar switch is nice, but the rest of the system is a nightmare to deal with.

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Old 02-28-2013, 11:39 AM   #2
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My Canbus keeps most stuff on for 60 secs after removing the key. It is a nice feature for GPS's, heated gear, lighting etc.

No idea about the 7.4v
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Old 03-03-2013, 03:04 PM   #3
JoelWisman
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Your looking at the ping the basic module sends out to see if the heated grips are there and flags a code if not. Since you understand thats its PWM controlled i'm guessing that will make sense to you which it fill to few others. If you look at the wave form on a scope things get truly interesting. The basic module sends a pulse somewhere around 100KHZ for some interesting feedback loop to estimate grip temperature and even powers down when it needs to for battery charging.
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Old 03-03-2013, 03:24 PM   #4
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Quote:
Originally Posted by JoelWisman View Post
Your looking at the ping the basic module sends out to see if the heated grips are there and flags a code if not. Since you understand thats its PWM controlled i'm guessing that will make sense to you which it fill to few others. If you look at the wave form on a scope things get truly interesting. The basic module sends a pulse somewhere around 100KHZ for some interesting feedback loop to estimate grip temperature and even powers down when it needs to for battery charging.
Wow, that's badass. I only know the high level concepts around CANBUS, but I think it's pretty cool. Maybe not the best thing for a bike that needs to be totally bulletproof, but I like not having a fuse box to worry about. I'm still waiting on the used grip to see if that sets things right, but knowing that the low voltage ping is normal makes me feel like it probably will.
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Old 03-03-2013, 03:48 PM   #5
JoelWisman
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Quote:
Originally Posted by ixab View Post
Wow, that's badass. I only know the high level concepts around CANBUS, but I think it's pretty cool. Maybe not the best thing for a bike that needs to be totally bulletproof, but I like not having a fuse box to worry about. I'm still waiting on the used grip to see if that sets things right, but knowing that the low voltage ping is normal makes me feel like it probably will.
Theres not actually any CANtalk to the grips though there is to the switch. The interesting functions are just how BMW programed the basic module and they really did put a lot of programming into the basic modules functions with respect to the heated grips.

If you want to know more about basic modules, root around on the web with reference to car basic modules. Basic modules have been used on cars since the early 1980's and are off the shelf control modules manufactures program for quite interesting functions of which replacing fuses, dumping copper weight by being remote controlled switches and self diagnosis are just a few.

In the world of industry the Programable Logic Controller (PLC) is the equivalent of a Basic module for cars trucks and motorcycles. Just a computer module that has a lot of generic inputs and outputs (digital and linear) that a manufacture then programs to do various things.

As for reliability, basic modules are old and trusted technology that is far more reliable then a bunch of manual power switches and fuses and gives you self diagnosis that manual switches will never have.

CANbus is just a communication standard that is also very old and very reliable though extremely slow and its not the only protocol BMW is using.

The vast majority of motorcycles have a basic module and have for a long time. Aprilia and Moto Guzzi installed basic modules 6 years before BMW did and they do happen to use CANbus as their main communication protocol.

You never hear anyone lament "new fangled CANbus systems" causing problems with Aprilia and Moto Guzzi because neither company has ever advertised that they use CANbus for anything.

BMW was years late to the game but chose to advertise old technology as something new and special and therefore has filled the web with comments about CANbus not being reliable LMAO

What BMW did do is put out some pretty buggy basic module firmware and even though it's not related to the CANbus communication protocol, people often blame CAN for their problems. They also did a poor job of training their sales and service staff what a CANbus is and therefore you read a lot of misinformation about what you can and can't do with a bike that uses CANbus protocol communication.

Aprilia and Moto Guzzi staff never misinform about what CANbus protocol does cause Piaggio group never bothered to communicate to franchises that their bikes use CAN
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