Gem Car Code 51 Help

Hi. I have a 2013 Gem Car. It’s 72v.

I initially had a failed motor so the controller was throwing a code, replaced the motor and then I got a different code that was suggesting I had a controller issue so I changed the controller then got a code 40 something sent it for warranty came back now I got a code 51 I can Not get to go away. I’ve sent this back to FSIP which is the company who makes the controller and they said that they have been tested it for a whole entire day and there is nothing wrong with the controller as is so they sent it back and I still have the same problem.
New battery’s.
New controller.
New key switch.
New motor

Apparently a code 51 is suggesting that I am not getting 72 V on pin one at the controller so I unplugged the connector took the pin out and inspected it and it looks fine and I also however have 72 V when I turn on the Key so I don’t know why it’s saying code 51 - I have no voltage at the controller unless I’m missing something. I’m hoping someone has come across something before and guide me in any direction cause I’ve exhausted all my resources…


Code 51 can be a vague one.

The contacts on the 23p controller plug need to be quite clean. If not they can cause a wild array of stray codes and many frustrated hours of chasing wild geese.
→ Give the controller plug and socket a spritz of spray contact cleaner. Skritch it on and off a bunch of times. Follow it up with a good blast with compressed air(plug and socket) and try it again. You may need to repeat this deep clean cycle a couple of times and finish it off with a light coat of dielectric grease and push it back on firmly.

I also however have 72 V when I turn on the Key so I don’t know why it’s saying code 51 - I have no voltage at the controller unless I’m missing something.

This is a confusing/conflicting statement. Can you clarify what you were trying to say here?

Which pin did you pull/check out of the controller?
Pin 1?
→ Also check for ~72 on P2.

→ Check fuse F13 on the PSDM. It powers the Main Contactor coil. Check for power at the coil (orange wire and B- ref). The controller Precheck might be looking ahead for power there. You should have close to ~72v all the way back to the controller at P17 (Key ON and no pedal press). When all codes clear P17 goes to 0 and contactor closes.

When does the code appear?

  • At key on? - then it is possible the code is not fully clearing. I have conflicting info on if this code is retained or tested every power up.
    → Try powering off with the main disconnect for several minutes(the manual says 15? but that sounds wayyyy long)

  • At pedal push?- Try removing one of the wires off your motor (A1 or A2), power cycle the car and try with the motor disconnected. Measure the resistance of the motor again. I know you said your motor was just rebuilt/replaced but the controller may still be detecting a problem downstream.


Thanks for reply

It happens as soon as I turn on the key.

Ive turned off the master for hours and still as the code.

Ive diagnosed this with a FSIP tech on the phone and all my readings are what they are supposed to be
::Key On::
Pin 1 to ground = 72v
Pin 2 to ground = 72v
Pin 3 to ground = 4.8v
Pin 4 to ground = 72v in fwd
PIN 5 to ground = 72v in reverse
Pin 6 to ground = 0v nothing in Fwd or Rev
Pin 7 to ground = .39v no pedal press, 3.6v pedal to floor
Pin 8 to ground = 0v
Pin 9 to ground = 5v
Pin 10 to ground = 72v
No pin 11 or 12
Pin 13 to ground = 5v
Pin 14 to ground = 0v
Pin 15 to ground = 10v
Pin 16 to ground = 0v
Pin 17 to ground = 72v
No Pin 18 and 19
Pin 20 to ground = 0v
Pin 21 to ground = 72v
No pin 22
Pin 23 to ground = -7.6v

Ive taken apart the connector and pulled out pins 1 and 2 and bent the contacts on them inwards to make sure they were seating and still nothing.

I found my PDSM yesterday smelt burnt when I put my nose to it so I decided to take it apart and did find a burnt section leading to the connector that goes out to the controller so I need to get another one of those fuse box assy’s. Don’t know if that’s going to solve my problem or if its just apart of the problem.

I Ohm’d out my motor with tech as well said readings were good and did all sort of wire disconnecting, wire swapping and still no luck.

How can I get a wiring schematic for this unit?

Post pic of PSDM internals.

Depending on what is burnt you may be able to jump that section and get lucky.
But otherwise this is a box full of magic that GEM has kept their cards fairly close to their chests about. Wiring diagrams show which pins go where, and somewhat relates to where it comes back out, but inside this box is a blank on how it is done. I don’t know why.

A visual inspection would expect some sort of processor in there, but only finds a few little tiny chips doing all the switching. To further the mystery, the builders even wiped most of the component ID numbers off the chips. Even running the traces is tough and doesn’t make sense most of the time so I think it is even a multi layer board.

In your case it doesn’t make sense as most of the PSDM is just for switching the 12v section of the car. If your pins on the controller all meter out fine then there is still something wrong.
**** BUT ****
(It is probably just a typo, but verify- )
In all of your tests noted above you ref to ground. This is incorrect. When measuring 72v you should always ref B-. When testing for 12v, you ref a gnd wire in that component or chassis ground.