Diagnosing Heated grips problem

Your trouble shooting looks intelligent.

BMS-K and ZFE are tough to trouble shoot if not impossible
mechanically.

In theory they should "solve" the problem electronically. (Factory/Dealer
G1 computer or maybe GS 911.

I doubt that the power wires carry any digital code but only respond to
analogue output from BMS-K or ZFE.

Check the ground for the "on" button...often a electrical achilles heel.

The heated grips over the last couple of years seem to be pretty trouble
free.

Wild Guess: The load or draw from the grips is to much for your alternator
output and the ZFE is just kicking the grips off line. This is prevalent in
some other scenarios where the BMW computers are logic driven to have plenty
of electrical power available for the combustion cycle to insure
smog compliance. If your running heated clothes unplug and see if grips
come back on line.

Actually two of your facts would feed into my wild guessing. 1) Both
grips go at same time. 2) Your having one hell of a cold spell.

Let us know what happens.

Unplug the switch at X9080. Measure between pin 8 (BROR) and pin 1 (SWBL) looking toward the switch. It should read open when the switch is off, closed when the switch is in position 1 AND position two. Between pin 8 and pin 5 (SWBR) should only be closed at when the switch is in position 2. That will tell you if the switch is OK.

X9080 is at the back of the switch. I don't know how hard it is to get access.

BROR = Brown/Orange wire
SWBL = Black/Blue wire
SWBR = Black/Brown wire

At least that is how I'm reading the diagram. I'm also assuming that it is the same for your '08 model. I know changes were made over the years but I've not seen an updated diagram (and I've looked!)

If the switch is OK then my GUESS is that you should see a voltage on pin 8 looking toward the BMS-K when the ignition is running. Again, that is only a GUESS.

If you have access to a GS-911 it might give you some diagnostics to help you figure out your issue.

pdxrmccgs/marc, thanks for taking the time to reply.

I'd already done initial testing on the switch so I knew that was OK. Also, I don't use any heated clothing or run any accessories that draw significant current (Starcom intercom and a small power socket for a GPS and that's it)

Over the last few days I've had the tank off and done some further investigations.

Before I started, there was no voltage at the heating elements regardless of the switch position and the engine running, revs etc.

The cold resistance of the left/right heating elements was measured at 7.2/7.4 ohms (which would draw around 2 Amps @ 14 Volts, producing around 30 Watts of heat per grip)

After removing the tank, I managed to locate the relevant connector (top one) on the ZFE controller. and checked all the wires from the switch and heating elements and confirmed there were no open circuits. all the connectors and harness were in excellent condition, no signs of corrosion, damage etc.

Unfortunately, as the tank was off, and also owing to the design of the ZFE connectors, it was impractical to try and run the engine and measure connections, so I gave up and put everything back together.

Once everything was back in place but just before I reconnected the heating elements, I took a further voltage reading on the heating element connectors and this time I measured 14+ Volts (Engine running) with the switch in position 2. When the switch was moved to position 1 (low power) the voltage remained at 14+ BUT was 'pulsing' at a frequency of around a second or so (difficult to say as I was just using a digital voltmeter) so it looks like the reduced heat mode is achieved by alternately switching the power on/off.

The final result is the grips are now working again.

I'm not particularly happy, because I found no problems in all the testing I done. My only explanations are that...

1) There is possibly a faulty connection on one of the wires and by removing/replacing the connectors and disturbing the harness etc, then I've temporarily made the connection again.

2) The removal of the connectors from the ZFE has removed power and possibly reset any error code in the unit.

3) There was some condition detected by either the ZFE or BMS-k module which inhibited the heaters and this condition has gone (for now), but in the abscence of any documentation I'll never know what these could be.

I've been for a long ride with a friend today, and the grips worked fine every time I tried them. The bike goes in for it's anual service in a few weeks, I'll ask them to check error codes etc, but I don't hold out any hope of getting a proper explanation.

Thanks again for taking the time to read/respond.

Regards,

Glenn

Hi Glen,

Just read your post, and you describe the exact same problem my 2008 GS had last november when temperatures dropped to near zero here in holland.

When ambient temperatures were above 10c the grip heaters were working fine.

I bought my bike in september last year and was covered by bmw warranty, so I went back to the dealers. They replaced the right hand side multi switch and everything was fine. Alas, for just 100 km. I went back again, the entire system was diagnosed much the same way you describe. Nothing was found wrong and when everything was put back together the heaters worked, just as yours did.

Again, after an hour driving they failed again. This time i called the dealer, and they got in touch with the berlin factory. And guesss what?

For the 2008 model (not the 2009 model) the factory has received a batch of grip heater resistors with a just too low resistance. They should be 7.8 to 8.2 ohms. Like mine yours are below that. Hence the current becomes too high according to the ZFE, which drives and monitors them.

There is a software update available for the ZFE that your dealer can install for you. I had it installed and since then the heated grips have worked flawlessly.

Regards,
Gert