Bad Boy Buggies - No Rear Drive, 4 flashes - FIXED

Golf Cart Wizard

Cartaholic - V.I.P.
Posting this in case it helps someone else. Even if you don't have a BBB this is still a good example why you can't just trust a code and replace the related part but should do a diagnostic.

Got a 4x4 electric BBB in, around 2007 I think. Has the dual Sevcon controllers. Customer complaint was no drive from the rear axle. First thing I did was pull the cover for a visual inspection. I noticed one controller had a steady green light, but the other was blinking 4 times. So I looked up the code and it said "Contactor welded or wiring fault giving a high voltage between M1 and B- before closing the contactor"

Now the first thing that I did was check the solenoid since that was what the code said. However, upon testing I found the contactor was indeed working properly, with 0 volts on the large post then going to 48v when the key was turned on. The rear contactor would then turn off after a few seconds and the controller showed the fault, whereas the front contactor remained engaged.

Now is when I had to start getting creative. If there is no voltage before the solenoid closes then why does the code say there is? You have to think about what parameter is the code looking for, "high voltage between M1 and B-". So I measure there and it is zero volts with the contactor open or closed. Now that alone should give away the problem, but let's think about the code some more first. So what does the controller define as high voltage then, and how is it measuring that? Maybe it is checking for change in voltage rather than absolute voltage, and it defines "high voltage" with the contactor open (zero) relative to the voltage with the contactor closed (still zero) rather than a minimum value, thus triggering the code due to no change in voltage.

But let's get back to the problem, if there is 48v at the solenoid output but 0v at M- what is in the circuit where the voltage could be lost? Obviously the wiring itself, as well as the electric motor armature. So I continuity checked between A1 and A2 and sure enough got "open circuit". Rebuilt the motor and now everything is happy, 4x4 and solid green lights on both controllers. Just goes to show why replacing a part just because a code shows that as the problem can be a waste of time