Originally Posted by
windancer
To start out, I want to say how valuable and informative this website is!! I have been “lurking” on SpyderLovers for quite awhile, but now have something to say….
My wife is on her 3rd Spyder (2018 F3t), while I have been riding BMW’s for almost 500,000 miles. My wife talked me into getting a Spyder. We bought a very nice pre-owned 2018 RTL from Proshop Motorsports in Henderson, Nevada. Good People!
The weather warmed up, and we went for a couple of rides. I noticed the cruise control wouldn’t engage. “Funny, it worked when I drove it home”. Then the bike went into “Limp Home Mode” a couple of times, with an code of C0040 and C006C. The bike then wouldn’t go faster than 59 MPH—not very safe when traffic is running at 70 MPH+! Anyway, I remember reading on Spyderlovers how to make “Limp Home” go away (turn key on/off three times, etc). The problem went away for a couple hundred miles, but reared its ugly head again yesterday. All this time the cruise control was DOA.
Researching on this site, I found that there are a few possibilities for this fault:
1. Blown fuse
2. Loose battery cable
3. Blown Brake Lite bulb
4. Bad Right-hand switchgear (Cruise Control)
5. Bad brake switch
6. ????
Now I’m a pretty good shade tree mechanic, and can fix most anything on a BMW. The idea of taking the RT back to the dealer for repair was the last thing I wanted to do. So I tackled the problem myself—with help from SpyderLovers and my downloaded Shop Manual.
Results:
1. Fuses were all OK
2. Battery cables were tight (new battery, kept on Tender)
3. Brake Bulbs are all LED, and functioning as they should.
4. Carefully took the Right-hand switchgear apart, sprayed it down with contact cleaner, and did a continuity test at the junction (located under RH fender). Everything was working fine.
5. Seems that the brake switch has been the problem for many folks. The Brake switch is located down there by the RH floor board. Gotta take off muffler, cat, etc – just to get to the (REALLY TIGHT) bolts holding the whole assembly to the frame. I learned a lot of new French-Canadian swear words, but eventually got to the switch. Actually, there are TWO microswitches on the 2018, both actuated by a ‘cam’ on the brake pedal. The one that typically fails is the one that controls the brake lite circuit and is triggered by the first little travel of the brake pedal—which is why you must make sure the pedal moves freely and completely returns to the ‘UP’ position, and that you don’t ‘ride the brake’. The other microswitch is actuated when the brake pedal goes all the way down (perhaps if your hydraulic system fails). Anyway both switches on my bike were clean and free from any debris. Cleaned with contact cleaner, bench tested with continuity tester, and everything check out OK. Lubed the moving parts, and buttoned it up. Bike didn’t throw a fault for several hundred miles, so I figgered it’s fixed. But still no Cruise Control. Oh well….
6. Then I read THIS THREAD started by Marvin2488485. A revelation!!
Here’s some help: the cruise control will not engage if there is anything amiss in the braking system. I studied the wiring schematic from my downloaded shop manual. I threw a voltmeter on the brake system wire (WHITE WIRE, located at the rear junction or one under the ass of the bike). It should read zero volts when bike is off or when the brake pedal is at rest (i.e. brake lights OFF). Then it should read 12-14 volts when brake pedal is depressed (i.e. brake lights ON). Well, it was showing ~ 5-6 volts ambient – brake pedal at rest/bike on. Hmmm. Why?? I reasoned that ANY voltage in that circuit when the brake is at rest will cause the computer to think that the brake is engaged, and thus prevent the cruise control to work. “If you’re braking, you can’t use the cruise control”. If the voltage is sufficient and consistent, the computer will think “Something is wrong. Let’s throw a fault for my owners safety, and slow him down to 59 MPH”.
Marvin mentioned that he had aftermarket brake lights on his bike, which were causing his fuses to blow (replaced by manufacturer, which solved his problem). I realized that my bike had two aftermarket brake lights: one on the tip of the rear fender, and a Custom Dynamics High-Mount Running/Brake light sold by Lamonster. Great lights. Real attention getters! Both are LED arrays. They are posi-tapped into the Brake Circuit (White Wire) for full brightness (BRAKE); The Running Lights use the same LED’s--via an in-line resister, tapping the Orange Wire circuit. Two diodes protect circuits from “backloading”. This in-line resister/diode set is very tiny, but essential.
I disconnected both auxiliary lights, and voila!! The White Brake Circuit tested 12 volts when brake pedal is engaged, and ZERO volts when at rest—as it should be!! ZER0, zilch, nada. The resister/diode thingy on the Custom Dynamics Light had failed--feeding voltage from the running light circuit back into the brake circuit. hence the computer thought the brake was always engaged, preventing the cruise control from even going on, and often causing the “Limp Home Mode”.
I buttoned everything up and took the bike for a test drive. Good News: I now have CRUISE CONTROL!!! I don’t expect to see the dreaded “Limp Home Mode” or the “C0040 and C006C” error code again.
Sorry this post is so long and technical. Hope this helps someone out there whose tearing their hair out. The rule: try removing aftermarket stuff to see if your problem goes away.
Did I mention how much I love SpyderLovers website??!!
