Helping the lady down the street with a Marathon

[rospaw]

Neighbor has a older 36v Ezgo marathon. She says for months it has been driving fine but only at 1/3 to 1/2 power. She said it just started one day after
her grandson drove it (10yr ish)

I drove it home and did some checking
Solenoid is clicking and reads battery V on both sides when pedal is pressed. (About 2v's less with no pedal.
Batteries 39v fully charged.
Wires seemed to be all snug and clean
Nothing looks out of place to these UNTRAINED eyes.

As long as you don't go past 1/3 / 1/2 pedal it will run all day long. Even pulled my driveway (very slowly) which is pretty steep. Once it drops out all you have to do is let off and press again and it will go again.
Where do i start?

Pictures ...... is this a factory dsc type controller?

Man code .... C1391 ...... sn 6214xx
p.s. i doing this as a favor / no money involved.

[rospaw]

Well, i thought i would put a pic ...... Not sure how to?

[orangeman6]

There's a little paper clip above the box you type in when you post. Click the little arrow next to it, then follow the prompts from there.

[cgtech]

Do the driveway check again, but floor it (since it will be crawling anyway), and monitor the voltage while climbing the hill. We want to see numbers at or above 31v. I think a battery may have crapped out. That would still allow the cart to run, but bad performance. Is this cart a resistor coil cart, or a solid state cart with a motor controller?

[JohnnieB]

Also might be the pot box type throttle is going over range.

Measure the resistance between the black and white wires with an Ohmmeter with the wires disconnected from the controller. Should be close to 0Ω with pedal up and about 5000Ω with pedal on floor. In reverse, it might be about half of that.

If the 0-5k throttle goes over about 7k, the controller will stop passing amps to motor.