How do you diagnose an electric vehicle?

Webmaster's picture

Hello all,this may sound like a silly question but, I am just curious as I have never owned an EV before, how do you all diagnose an electric vehicle when you run into a problem with the computer, especially when you get a "yello wrench" error message. Is there some special computer that you all use to diagnose? Now I work in an automotive shop and all we work on is ICE's and I am aware of how to diagnose an ICE vehicle because they have computers in the cars to diagnose them properly. Is it the same as diagnosing an ICE?
Just curious! Thanks for everyone's time.

Lisa ~

before comments


Mik's picture

And how do you diagnose a subtle spammer?

This information may be used entirely at your own risk.

There is always a way if there is no other way!

And how do you diagnose a subtle spammer?

Possibly true Mik, but on what basis do you ascertain that Lisa is a spammer?


reikiman's picture

And how do you diagnose a subtle spammer?

Possibly true Mik, but on what basis do you ascertain that Lisa is a spammer?

FWIW the posting fits some of the criteria of posters who join and make postings just so they can post a link to their website. However in this case Lisa is a friend of mine and it's probably 99% likely she's not spamming us, but is really interested in the question she posted.

In any case the answer to her question of course depends on the design of the specific vehicle.

A homebrew conversion like the ones I've done (and she's seen) -- well -- diagnosing that is done with simple tools like a multimeter or visual inspection of cables.

But one hopes the commercially made vehicles have better diagnosis features. CAN Bus etc. On cars there is the OBD-II port that's a standard that I've never used, and is the way to hook into onboard computers. I wonder if that port exists on commercially made electric cars? A quick search indicated that it is.

For the EV's from major car companies there is training going on for repair and maintenance. Shops like the one owned by Lisa's family might not be seeing these cars for awhile, however.

THANK YOU David for standing up for me.
Yes I am a real person not a spammer hahahah.
Don't worry I am not offended. I was just curious on how ya'll diagnose electric vehicles. The only electric vehicles my shop has seen are the Toyota Prius. My shop also is not equipped to handle full electric vehicles.
We are only equipped to handle ICE's.
I have been a service writer for my shop for over a year now. I used to deliver auto parts from a distributor warehouse. But my background is primarily law enforcement and security. I am learning quite a bit while working for my family's shop. I have never even heard of electric vehicles till I met my friend David again. He introduced me to them and I got somewhat involved in them with David.
They are very interesting to me and I hope to learn more on this amazing website that David created.

Yes I am a real person not a spammer hahahah.

Well, there y'go. Welcome Lisa! I hope you will forgive Mik his sceptism, but spammers do seem to be becoming more prolific.


Hiya Lisa,

As a beta-tester of a new electric scooter model, I've now got some first-hand experience with this exact problem. The engineers were up in Ann Arbor, MI, and I'm down in Atlanta GA. So I had to do the first round of diagnosis myself, just to get the process started.

First, this type of problem is going to be very different depending on how the bike is built. Simpler bikes will just fail, more complex ones may have some sort of onboard diagnostics that tell you where the problem is. But even reading onboard diagnostics may involve things like counting blink codes. I had a problem with the controller, and I had to look under the plastic bodywork and observe a LED that flashed 4 times, paused, and then flashed twice more. This code indicated a failure in the hall sensors, meaning that I needed a repair to the electric motor itself. My bike also has a flashing LED on the dash, which can indicate about a half-dozen other locations for possible errors.

Mostly, diagnosing is just a matter of carefully observing what works vs what fails. For example, if the bike won't move, are the 12-volt power systems still working? If you still have headlights and instrumentation, then power is flowing in at least part of your electrical system. That narrows down the possible locations of a failure. There are often safety switches on the bike, to disable the electric motor when the brake levers are pulled, or when the side-stand is down. I verified that the brake lever switches were working by checking the tail lights. Maybe the bike will drive in reverse but not forward? Or it runs fine when the bike is cold but rapidly loses power after 10 minutes of riding? Maybe you can climb a steep hill on a cold day but not on a hot one? I had a brief loss of power under heavy throttle when the bike was really cold, problem went away when the battery pack was warmer. (This was a combination of voltage sag from load and cold-weather voltage drop combining to trigger LVC.)

The nice thing about electric vehicles is that they are an order of magnitude simpler than your standard internal combustion driven vehicle. So most problems can be isolated with a little bit of careful observation, and possibly a simple tool like an electrical multi-meter.

When dealing with errors coming from a onboard computer, there's no real standard yet. A nicer computer will have a way of giving an error code to the user, either with an indicator on the vehicle dash or by using some type of plug-in diagnostic port. And while there's a standard interface for diagnostic ports in automobiles, that standard isn't often used on motorbikes. Ideally, a modern onboard computer would have a small wifi chip, and send it's diagnostic information directly to an app on my smartphone, but that's probably got to wait until these vehicles are a little more mature.

My electric vehicle: CuMoCo C130 scooter.

:) Thanks Marcopolo

Hi Mike! Thank you for the info I do appreciate it. It is very interesting stuff compared to what I normally deal with at the shop when you diagnose an ICE. Pretty cool thanks :)

Lisa ~

I appreciate everyone's comments! Thank you (as I am still learning)


The shop protocols you see everyday with your ICE's are the end result of 100 years of development and refinement. Electric vehicles today are much more like the world of 1911, when each vehicle was the result of its own technology. I had a neighbor that was a boy around 1911 when a customer brought a Stanley Steamer into his father's blacksmith shop and asked him how to operate it. His father sat back and traced the elements, finally firing it up and taking it out for a ride with his son (to the son's everlasting thrill) to verify that he knew how to operate it.

There are two sorts of vehicles you'll be dealing with: homebuilts and major manufacturers'. In practice, the Chinese scooters are far closer to homebuilts.

For the homebuilts, you will have to diagnose and repair based on first principles. You will need to know the design and function of all the relevant parts, and how they interact.

For the majors, you will have to study their diagnostic literature and/or get their certification to understand the individual design. Having a cert for a Prius will not help you a lot with a Volt.


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