I’ve had family visiting and the 2008 GEM has been great fun for them until last night immediately after unplugging from a full charge on the SDI battery pack.
Has anyone else had this happen and ID the source(speed sensor, MM or controller)? This is not the first time I’ve fully charged the battery. Symptom was: the GEM immediately dropped to Turf speed, display showed 81 and the wrench indicator was showing. Power cycle never showed any KPH number other than zero and quickly drops to Turf speed.
Instead of testing the speed sensor with a DMM I figured I could just swap out the Magic Magnet and see if the display will show speed and it does.
So it looks like the Magic Magnet failed. I did put it back in the circuit and tried it and got the 81 code again and 0 speed. Looked and found it’s potted so I can’t figure out what failed nor repair it.
I will look more closely at the pins and sockets with a light and a magnifier.
I’ve also worked the 3 switches back and forth and will retest once I finish charging the EV in the driveway.
@Inwo I checked all pins and sockets and all are shiny metal and saw now water ingress indications. I also retested after working the switches and still zero kph when moving.
As can be seen in the pic above, it has been secured to the frame and resting against the shock tower so couldn’t move much. I’ll box it up and send it out once someone verifies I have the address correct.
My guess is something right on the edge of not working. The MM requires power from red wire. You could check voltage with and without MM. The controllers are skimpy supplying power to the hall effect.
I measured 12.7V(black to red wires) from the car(disconnect from speed sensor) and then with the MM connected and at the speed sensor end I measured 11.6V
I didn’t want to probe into any wires or through any seals to get measurements with the speed sensor connected.
Use a sharp pin in the red. It will heal well enough. The important measurement is fully loaded.mm connected to motor sensor. It will pull down below10v. Then with only motor sensor connected. Est to be over 10v.
In theory oem sensor should work down to a little over 5v.
These are tests that I can’t do on the bench. If yours tests bad, it’s an easy fix. If tests good, a replacement may not work either.
It’s been a couple years since I found a bad one. Similar to your dilemma. Tested fine here. Haven’t heard back after replacement.
At least we know mm is not shorted or open.
“measured 12.7V(black to red wires) from the car(disconnect from speed sensor) and then with the MM connected and at the speed sensor end I measured 11.6V”
That doesn’t sound good. @AssyRequired . The voltage should not change when contactor pulls in. IMO
There is no electrically common components, between driving and the speed sensor. Let me think.
The sensor 12v comes from the internal 12v regulated bus. Regulated down from B+ 72v battery. The bus has a 5v regulator connected to 12v bus for supplying power to throttle and internal 5v housekeeping. There is no lack of voltage available (72v source). I can test throttles and speed sensors with only 30v B+ at pin 1.
I don’t know minimum voltage requirement for the 12v hall sensor. The MM will work down to 7.5v. From your test, 11.6v with mm connected, and now 8.5v after connecting hall sensor. It could be either the controller aging power supply or the sensor drawing a little more current. Or possibly 8.5v is ok and MM just died. We will soon know.
ps. 8.5v is still enough to supply 5v circuits in controller and 5v throttle.
I think this is a 2008, Yes? If someone else with a MM will post red wire volts, it will help me out. Test between MM and motor. Use B- or black wire as reference.
It’s all worked fine upto the other night just after it had finished fully charging the SDI battery.
I pulled out of the driveway, a car was coming down the street behind me(on a slight hill) so the only thing I did which I don’t do often is I went from Reverse to Forward without a stop in between. As I started down the hill it went into Low speed instead of the normal High speed it was switched into. Headlights were on and didn’t change brightness to my understanding.
Is there any chance the motor shaft could have moved so much it damaged the sensor? A fully charged SDI usually gives me a good amount of torque… I just don’t see what could have triggered any of this to happen after working great for so long.
