66 error code

I have a 2002 Gem Car that did something very strange today. Started down a decent steep hill today, and it picked up good speed. All the sudden the dash indicator lights started flashing and it just quit.

Now it will go into reverse, but every time I switch to forward, it kicks out and a -66 error code pops up.

Tried it several times but no luck. Rode home on a flat bed wrecker…

Im new to Gem cars, but I feel it had something to do with maybe going down hill too fast. But I may be 100 % wrong.

Any advise would be greatly appreciated.

Anything can push a failing part to die.
It seems field transistors are shorted in controller.
Full bridge uses a different pair for F and R.
Repairable if you know someone handy with electronics.

Rodney can get it rebuilt.

In this thread it lists -66 as “Field Current High” inspect motor controller. Here is a link to all the GEM codes

Took the dash out this morning and when the units kicks out and then shows the error code 66. The Main Contactor is whats kicking out. Like I stated this stays engaged if I put in reverse.

Forward and reverse are seporate citcuits

Shorted field transistors. See second post.

so an option I did get from a local guy that also has a Gem car is to send my controller to RIDEFORFUN they will rebuild it for $500.00 dollars.

Seems pretty high for a rebuild. But is this my only option?

I can replace them for $150 but it’s not a rebuild. Just replace the parts.
As in post 2, if you know someone handy with electronics, Ill show you how.

Thank you INKO…that obviously sound much better. I have to be out of town for a couple of days, and if its ok, I will reach out to you when I return to see if we could accomplish this.

Thanks again, I really appreciate your help.

I had the car shut down earlier this year when going down hill. It was a -76 voltage too high regenerative braking. I couldn’t get it going again for awhile. Had to shut the car off I think then it would go forward. That got me worried for awhile. So I can go exactly 31 mph but when it hits 32 bam, it shuts down. That’s actually plenty fast in this thing so I try to keep it at 30 or below.

Maybe a thermal switch is engaged? It indicates cleaning contacts or yeah, you might have a damaged controller. I had mine rebuilt at RFF, 500.00 but I knew mine was bad because it popped. Sat too long.

INWO repaired my 66 error a couple of years ago


I backed out of my driveway yesterday and when I placed it in forward, it stopped and gave me the 66 code…can you help me?

INWO can repair your controller cheaper than FSIP. This is a common problem.


It can be a simple fix if a field transistor is shorted. Do you know an electronic hobbyist that might tackle it?
@MikeKC is attempting a repair. If he’s successful it may be something that he would take on.

Strange timing. This happened to me today too.
I drove down to the corner store for beer and came back to a code 66 and then a code 51. Had to tow strap it home.
I gotta be more careful. I’m pushing things too hard. Good thing I have a backup controller so I can tear this one apart and look for poopie stains.

4 on one side and 2 on the other in parallel groups. If shorted, clip leads until you find which it is. Or change them all. Look for higher voltage mosfets with lowest on-resistance you can afford.

From my notes:
80amps 120v .018ohms are stock.


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Unfortunately I do not…I’m not even sure where the controller is???

What year Gem?..

I diode checked all the mosfets and one of them reads nothing. The rest all read .46 - .40.
So I need to replace the 4 and 2 for this grouping?

They are in parallel groups as I recall. Meaning more than one should show shorted.
First 4 on one side and 2 on the other side should be the same part number for the field.
The only way I’m confident is to clip a lead. If it still shorted, you know for sure it’s that one.