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2009 Miles ZX40ST; barely moves troubleshooting

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Recently purchased ZX40ST that will move forward at about 1mph unless there is an incline which brings it to almost a complete stop unless the grade is to steep which will keep it from moving forward at all. It seems to perform only slightly better in reverse.

I have power at top of the controller: 13.7vdc B+/-, ~68vdc B+/- (havent charged since I brought home last week), ~30vdc B-/U,V,W. Haven't tested at motor poles.

I do not hear a contactor when I press throttle down, should it be audible when first pressing on pedal? Vehicle moves barely, almost not at all, which tells me I have an issue somewhere in the control, tps, contactor, ac motor or perhaps Regen circuit.

I'm learning as I go. All systems seem to be untampered with and it has just under 3k miles. Looks like the batteries where replaced mid 2012 and seem to be holding up to at least get this thing operating at normal speed.

First thought is bad coil in contact or perhaps bad contact armature.
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· Registered
1,024 Posts
Sounds like it has failed batteries, voltage should be 76 volts plus.

Also these cars commonly have wire coorsion issues along the steering column and pedals, new grounds are a pretty common need as well.

Start cleaning plug in connectors and rerunning grounds, the main contactor can coorode our as well making it useless

Good Luck

· Registered
3 Posts
Discussion Starter · #3 ·
Thanks for the quick response!

I am charging now, haven't done this yet because when I bought it key on had +70vdc at B+/- and the aux 12v battery has maintained 13.7vdc for about six days with me checking all the systems.

The batteries are going to need replacing soon, I just wanted some more time to see if all other circuits, relays/switches, and components are good before I decide to buy $2600 oem replacement batteries. Or if other main components are in good working order I may feel confident enough to invest in my first Lithium ph pack and peripherals.

So I guess because I bought this in the condition it's in I want to trouble shoot the main traction components from least expensive to batteries because I'm not sure what normal operation sounds like, feels like, or looks like.

When I turn key on can hear contactor (sounds weak imo) if it is the 72v contactor under ebrake near bus bar. I can't tell if its coming from the DC/DC inverter or Curtis control but for such a large contactor it sounds weak.

The service manual says the contactor relay is closed when the key is on but that does not sound like a HV contactor or main contact. My only reference for the whole gas pedal pressed equals contactor drop is a golf cart, the only thing I can barely hear when pushing down pedal is the tps plunger NO contactor. Shouldn't I hear a contactor drop?

I will be cleaning all terminal and a replacing some of the 32v fuses because they are visibly corroded but not broken or burnt.

Thank you for your experience and time!

Because it moves at all makes me feel good about stepping out to learn more about this system and hopefully when I grow up I will be better educated so I can start converting and building other ideas.

I'm a beginner and learning as I go.

· Registered
16 Posts
I owned a 2009 ZX40ST in San Diego for about a year before I sold it a few months ago. I'm a dealer and saw it at a local Copart and bought this mostly out of curiosity.

Your 1mph speed is just a matter of low batteries. Mine used to do this after I let it sit for a while. That 72V->12V DC/DC converter is constantly on, which does drain the large batteries. I wish there was some advanced electronics to stop overcharging. I guess charging it nightly was supposed to be a OEM solution for this

Getting to the batteries wasn't easy. Required a car lift, removing the driveshaft and then a hydraulic table/jack to bring them down.

I had my truck on scales with one driver and this camper top on it, and it scaled at 2980 lbs. And it has the GVWR of 2,990 lbs, so it makes you wonder...

$2600 is a lot of money for just 6 lead acid batteries, I hope you find a cheaper or better solution.


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