EV Diagnostics
Two things owners ask before anything else: what does it cost to find the fault, and is my battery actually degrading. Both have real answers. The first is a fixed price told to you on the phone. The second is a measurement, not an opinion.
Message us about your EV
Send the model and what it is doing. You will get a straight answer.
or call 01744 808586
WHERE TO START
Most dead EVs are a flat twelve volt battery
The cheap battery causes the expensive-looking problem.
The single most common reason an electric car will not start is the ordinary twelve volt battery. Not the expensive one under the floor — the small conventional battery that wakes the electronics, closes the contactors and lets the high voltage system come online at all.
When it goes flat the car does nothing. No lights, no response, no way in through the app, and a drive battery three quarters full makes no difference whatsoever. Owners understandably assume the worst and start pricing packs. It is the same battery, the same failure and roughly the same cost as on any petrol car.
That one fact reframes most of what arrives here. A great deal of what looks like an expensive electric car problem is an ordinary car problem wearing unfamiliar clothes, and it is diagnosed the same way. See car battery replacement and car diagnostics.
HOW WE WORK
What EV diagnostics actually involves
Three things that decide whether this costs you anything much.
A fixed price to find it
Told to you on the phone before you commit. Electric vehicle fault finding is not open ended here and it is not billed by the hour.
Battery health measured
A real capacity figure from the battery management system, not an estimate from the range display or an opinion about the weather.
Everything else still applies
Tyres, brakes, suspension, steering and an MOT every year. An EV needs all of it and none of it needs a specialist.
ev diagnostics
SYMPTOMS
Every EV symptom, and where the fault usually sits
Eight complaints, and how few are about the drive battery.
This is what electric cars actually arrive with, and where the fault usually sits. Note how much of it has nothing to do with the high voltage system.
| What the car does | What it usually is | What it means |
|---|---|---|
| Completely dead, app will not connect | The twelve volt battery | By far the commonest complaint. Ordinary part, ordinary price, and no relation to the drive battery. See car battery replacement |
| Several unrelated warnings at once | Low voltage, or one poor earth | On a car with this many modules a weak twelve volt battery produces alarming nonsense across systems that are perfectly healthy |
| Flat after standing a week or two | The twelve volt battery, or something not going to sleep | Measurable rather than a matter of opinion, and worth doing properly before buying anything. See battery drain diagnosis |
| Range has dropped noticeably | Cold weather, in the great majority of cases | Every EV loses usable range in winter and recovers fully in spring. Persisting through summer is different. See EV battery health check |
| Charging slower than it used to be | Temperature, the charge point, or state of charge | Charging slows deliberately as the pack fills and when cold. That is protection working. See EV charging fault diagnostics |
| Will not charge at one location only | The charge point, not the car | Charge points fail quietly and stay lit. If it charges elsewhere, the car is almost certainly innocent |
| Brakes fail the MOT with plenty of pad | Disc corrosion from regenerative braking | The discs are barely used so they corrode instead of wearing. Catches almost every EV owner out once. See MOT |
| Tyres worn out sooner than expected | Weight and instant torque, not a fault | EVs are heavy and deliver torque immediately. Tyre life is genuinely shorter. See tyres |
WORTH KNOWING
An electric car still needs an MOT every year
It surprises a number of owners, particularly those who came to electric cars through leasing and never dealt with a test. An electric car takes its first MOT at three years old and every year after, exactly like a petrol one.
The only part that does not apply is the emissions test. Everything else does: lights, brakes, tyres, suspension, steering, structure and any illuminated warning lamp. In practice brakes and tyres are where these cars get caught, for the reasons set out above, and both are worth checking before test day rather than on it. See MOT.
THE PROCESS
How EV diagnostics runs here
Six steps, and the expensive battery is not among the first.
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What the car is actually doing
Dead, warning, range or charging. Those four route the entire job, and three of them rarely involve the high voltage system at all.
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The twelve volt battery, load tested
Not a resting voltage reading. A proper load test, because this single item explains a large share of what owners arrive worried about.
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Full system scan
Every module rather than one. Warnings on these cars frequently originate somewhere other than where they appear on the display.
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Battery state of health where relevant
A measured capacity figure from the battery management system rather than an estimate from the range readout, which reflects weather and driving.
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Charging behaviour if that is the complaint
Whether the fault is the car, the cable or the charge point, established rather than assumed. See EV charging fault diagnostics.
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An honest line on what is ours
Where a job genuinely needs manufacturer level intervention you hear that plainly, with what we would do in your position. Ring 01744 808586.
COST
What electric vehicle fault finding actually costs
A fixed figure, told to you before you commit.
The honest answer is that the diagnostic is a set amount, quoted on the phone before you bring the car, and it folds into the repair if the work goes ahead with us rather than being charged twice. There is no hourly meter and no version of this where the figure moves once the car is here.
What surprises owners is how often it ends there. A twelve volt battery, a charge point that had already failed, a cable with a damaged pin, or a winter range drop that is not a fault at all — between them those account for a large share of what arrives. In those cases you pay for the hour and take the car away working.
Where genuine high voltage work is needed, you get the figure and the reasoning before anything starts, and you are free to go away and think about it. For larger repairs there is Payment Assist on a soft search rather than a full application. See repair costs.
BATTERY HEALTH
Has the battery degraded, or is it just winter?
A measurement settles it. The range display cannot.
This is the question behind most EV worry, and it is genuinely answerable. Cold does two things at once: it reduces the usable capacity of the pack, and it increases consumption because heating the cabin draws from that same pack. Together they take a real bite out of what the car will do on a charge.
It is temporary. Nothing has been lost and it all comes back as the weather warms, which is why so many owners worry through a winter for nothing. The trouble is that the range estimate on the dashboard is a prediction shaped by recent driving and temperature, so it confirms the fear rather than settling it.
State of health is different. It reports the percentage of the pack original capacity remaining, measured from the battery management system, and it does not move with the seasons. That figure is worth having when you are selling, when you are buying, and when you are deciding whether to keep the car another few years. See EV battery health check.
SERVICING
What an electric car still needs servicing for
Fewer moving parts is not no moving parts.
An electric car has fewer moving parts, not none. Everything below still wears, still fails an MOT and still needs somebody to look at it, and none of it requires a manufacturer service point.
Brakes
Used less because of regenerative braking, so they corrode rather than wear. That is an MOT failure with plenty of pad left. See MOT.
Tyres
Heavier car, instant torque, shorter tyre life. Correct load rating matters more than on a petrol car. See tyres.
Suspension and steering
Carrying significant extra weight over the same components. Bushes and bearings work harder than the mileage suggests.
Cabin filters and fluids
Brake fluid, coolant for the battery and motor, and cabin filters all still have intervals. See car servicing.
The twelve volt battery
The commonest failure on the whole car, and an entirely conventional part. See car battery replacement.
The annual MOT
From three years old, exactly as any other car, minus the emissions element. See MOT.
GO DEEPER
EV diagnostics by make and by fault
Where a specific page covers it in more detail.
- Battery health check — A measured capacity figure you can keep and show a buyer. See EV battery health check.
- Charging faults — Whether it is the car, the cable or the charge point. See EV charging fault diagnostics.
- Tesla — Model specific faults and what an independent can and cannot do. See Tesla diagnostics.
- Polestar — Very few service points nationally, and a lot of ordinary work that never needed one. See Polestar diagnostics.
- Hybrids and plug-ins — A different set of questions again, and often a cheaper answer. See hybrid diagnostics.
- Battery drain diagnosis — For a car flat after standing rather than a charging fault. See battery drain diagnosis.
Owner questions
EV owner questions, answered
Fifteen questions electric car owners actually ask us. If yours is not here, ring 01744 808586.
Almost certainly not the one you are worried about. On an EV the usual cause is the ordinary twelve volt battery, which wakes the electronics and brings the high voltage system online.
With that flat the car does nothing at all, however full the drive battery is. It is a conventional part at a conventional price. See car battery replacement.
A set figure quoted on the phone before you commit, and it folds into the repair if the work goes ahead here rather than being charged twice.
There is no hourly meter. A fair share of EV complaints end with no parts at all, in which case you pay for the hour and drive away. See repair costs.
Yes, for the great majority of what one needs: brakes, tyres, suspension, steering, filters, fluids, the twelve volt battery, the MOT and reading the car properly.
Where a job genuinely needs manufacturer level intervention we say so plainly rather than have you bring the car for nothing. See car servicing.
Yes, from three years old and every year after, exactly like any other car. The only difference is that the emissions element does not apply.
Everything else does, and brakes and tyres are where EVs actually get caught. Worth checking before test day. See MOT.
Usually not. Cold reduces usable capacity and raises consumption at the same time, and it all comes back when the weather warms.
The range display is a prediction, not a measurement. State of health gives you a real figure that does not move with the seasons. See EV battery health check.
By having it measured from the battery management system rather than estimated. It reports the percentage of original capacity remaining.
It is the number worth having before you sell, before you buy, or when deciding whether to keep the car. See EV battery health check.
Because regenerative braking does most of the slowing, so the discs are barely used and corrode rather than wearing.
It feels wrong because the car stops perfectly well, and it catches almost every EV owner out once. See MOT.
Weight and instant torque rather than any fault. An electric car is considerably heavier than its petrol equivalent and delivers its pull immediately.
Fitting the correct load rating matters more than on a petrol car, and the wrong tyre is a false economy. See tyres.
Try a different location first, because that single test costs nothing and resolves a large share of charging complaints.
Charge points fail quietly and often stay lit as though working. If it charges elsewhere the car is very likely fine. See EV charging fault diagnostics.
Frequently nothing is wrong. Charging slows deliberately as the pack fills and in cold conditions, and it drops steeply above about eighty percent.
That is protection rather than degradation. If it has genuinely changed in like for like conditions, that is worth reading. See EV charging fault diagnostics.
Either the twelve volt battery has reached the end of its life or something is staying awake and drawing from it. Both are measurable.
A proper drain test separates them rather than guessing, which matters because otherwise people buy two batteries. See battery drain diagnosis.
No, provided the schedule is followed with the correct parts and the work is documented properly, which is how we do it.
That applies to electric cars exactly as it does to petrol ones. Ring 01744 808586 with the model and we will tell you what the schedule asks for. See car servicing.
Most of them, and we will tell you honestly on the phone where we cannot rather than after you have made the journey.
There are dedicated pages for Tesla diagnostics and Polestar diagnostics covering what is model specific about each. Ring 01744 808586.
They can be very good value, and the one thing worth establishing before you commit is the battery state of health rather than the mileage.
Check the brake discs too, because low pad wear on a high mileage EV is not the good news it looks like. See EV battery health check.
The model and year, and which of four things it is doing: dead, warning, range or charging. Those four route the whole conversation.
If it is dead, say how long it stood beforehand, because that points immediately at the twelve volt battery. See car diagnostics.