EV Diagnostics: What Your Scanner Can (and Can't) Tell You

Your OBD-II scanner is brilliant on your Golf. Plug it in, read the codes, get a clear picture of what's wrong. Then you try it on an electric car and the thing basically shrugs at you.

I learned this the hard way last spring. A friend asked me to check his 2020 VW ID.3 before he sold it. I brought over my trusty Bluetooth adapter, connected my scanner app, and started scanning. The app pulled up a couple of generic P-codes (both old, both cleared) and some basic live data. But the one thing we actually wanted to know, how healthy the battery was after four years and 78,000 km, was completely invisible. The battery management system, the motor controller, the thermal management loop: all locked behind VW's proprietary protocols. My scanner might as well have been a paperweight for the questions we were asking.

That experience sent me down a rabbit hole that I'm still in. And if you're reading this, you're probably in the same spot: you own or you're buying an EV, you want to understand what's going on under the skin, and you've discovered that the consumer diagnostic tool ecosystem for electric cars is years behind what we've had for petrol and diesel vehicles.

Let's talk about what actually works, what doesn't, and where the gaps are.

What OBD-II Can and Can't Do on Electric Cars

Every EV sold in Europe still has a standard 16-pin OBD-II port (with one notable exception we'll get to). That port is legally required for emissions-related diagnostics, which is why it exists on EVs even though they have zero tailpipe emissions. Manufacturers still use it for certain powertrain fault codes and basic data streams.

Here's what a generic OBD-II scanner can typically access on an EV:

• Generic powertrain diagnostic trouble codes (P-codes)
• Some basic live data parameters (coolant temp, voltage readings)
• Readiness monitors
• 12V battery system data

Here's what it can't touch:

• Battery management system (cell voltages, state of health, temperature distribution)
• Motor controller data (inverter temps, power output, efficiency)
• DC fast-charging parameters
• Thermal management system status
• Regenerative braking calibration
• Most manufacturer-specific fault codes

That second list is basically everything that matters on an EV. The battery pack is worth €4,500 to €18,000+ on a passenger EV, it directly determines range and resale value, and your generic scanner can't tell you a single useful thing about it.

For ICE cars, we've had affordable, accessible consumer diagnostic tools for over twenty years. For EVs? We're starting from scratch, and the tools that do exist are fragmented across individual manufacturers. It's genuinely frustrating.

The 12V Battery: The One Thing Your Scanner CAN Help With

Before we get into the specialist tools, let's talk about something that catches a lot of EV owners off guard: every electric car still has a conventional 12V lead-acid (or lithium) battery. And when it dies, things get weird.

Unlike a petrol car where a dead 12V battery just means the engine won't crank, a dead 12V battery in an EV can produce bizarre symptoms. The dashboard goes dark. The car won't shift out of park. The charging port won't open. The high-voltage contactors can't close, so the car is completely immobilised even though the main battery pack has plenty of charge.

There's a thread on r/electricvehicles that gets linked constantly: someone's ID.4 or Model 3 goes completely dead in the driveway, they panic about a €15,000 battery failure, and the answer turns out to be a €90 12V battery that lasted three years instead of five.

This is genuinely the most practical thing a standard OBD-II scanner can do on an EV. Monitor the 12V system voltage, watch for slow cranking of the DC-DC converter output, and catch a failing 12V battery before it leaves you stranded. It's not glamorous, but it'll save you a tow truck call.

Vehicle-Specific Tools: What Actually Works

Since the generic OBD-II ecosystem falls short on EVs, the community has built model-specific solutions. Some are excellent. Others are expensive. Here's the landscape for the most common EVs in Europe.

VW Group (ID.3, ID.4, Skoda Enyaq, Cupra Born) + OBDEleven

The VW ID platform is the best-selling EV architecture in Europe, and thankfully it's one of the more open platforms for diagnostics.

OBDEleven (€60 for the basic device, €115 for the Pro) is the go-to tool for VW Group EVs. It can read battery state of health, individual module voltages, thermal management data, and a deep list of manufacturer-specific codes. It also handles coding and adaptations if you want to tweak comfort features.

For ID.3 and ID.4 owners specifically, OBDEleven gives you the battery SOH percentage that VW hides from the dashboard, cell group voltages, coolant temperatures, and charging history data. The community on the VW ID forums has documented most of the useful PIDs, so you're not starting from zero.

One caveat: OBDEleven's EV coverage is still evolving. Some parameters that work on an ID.4 Pro don't work on the ID.4 GTX. Check their compatibility list before buying, and expect periodic app updates as they expand coverage.

Nissan Leaf + LeafSpy Pro

The Nissan Leaf has been on European roads since 2011, and it has a well-known weakness: battery degradation. The pre-2018 models (24 kWh and 30 kWh) lack active thermal management, which means hot climates and frequent fast-charging take a real toll on the pack.

LeafSpy Pro (€15-20 app plus a €25-40 compatible Bluetooth adapter like the OBDLink LX) is the definitive tool for Leaf diagnostics. It reads individual cell voltages, precise SOH percentage, temperature data across the pack, cumulative quick-charge counts, and total energy throughput.

I ran LeafSpy on a used 2017 Leaf 30 kWh that a colleague was considering last autumn. The dashboard showed 11 out of 12 bars, which could mean anything from 78% to 85% SOH. LeafSpy reported 72.4% SOH with two cells significantly weaker than the rest. At 72%, that 30 kWh pack was effectively a 21.6 kWh pack. The range in winter would be around 100 km, maybe less. My colleague walked away from the deal.

The consensus on SpeakEV (the major UK/EU EV forum) is simple: any used Leaf without a LeafSpy report is a gamble. The app costs less than a single tank of petrol. There's no excuse for skipping it.

My honest opinion? LeafSpy should be considered mandatory for any used Leaf purchase, full stop. Not "recommended," not "helpful." Mandatory. The difference between a 85% SOH Leaf and a 72% SOH Leaf is thousands of euros in value and the difference between a usable car and a city-only runabout.

Tesla + Scan My Tesla

Tesla is the most locked-down platform for consumer diagnostics. And this is a real problem for used car buyers.

First, the hardware situation. Tesla Model 3 and Model Y don't use a standard OBD-II port for their primary diagnostics. They have a proprietary diagnostic connector that requires a specific adapter cable (around €20-35) to convert to a standard interface. Model S and X pre-2021 had more accessible OBD-II ports, but post-2021 models also moved to different connectors.

Scan My Tesla (roughly €10 for the app) is the most popular consumer tool for Tesla battery diagnostics. It reads cell voltages, pack temperatures, SOH estimates, motor and inverter data, and various other parameters that Tesla's own app doesn't expose. But here's the total cost people get wrong: you need the app (€10), the proprietary adapter cable (€20-35), and a compatible Bluetooth OBD adapter like the OBDLink MX+ (€75-95). All in, you're looking at roughly €100-140, not the €45-90 figure you'll see quoted on some blogs.

For a Tesla owner monitoring their own car over time, Scan My Tesla is worth the investment. For a used Tesla buyer doing a one-off inspection, the cost and complexity of the setup is a barrier. And Tesla's general attitude toward third-party diagnostics (locking down data, requiring proprietary connectors) makes the used Tesla market less transparent than it should be.

Strong opinion here: Tesla's locked-down diagnostic approach is anti-consumer. When you're spending €35,000+ on a used Model 3, you should be able to verify battery health without buying €140 worth of adapters and cables, or paying a Tesla service centre for the privilege. Every other major EV manufacturer provides at least some battery data through standard tools. Tesla makes you jump through hoops, and used buyers pay the price in uncertainty.

Hyundai-Kia (Ioniq 5, EV6, Kona Electric, Niro EV)

Good news for Hyundai-Kia EV owners: these are among the most open platforms for third-party diagnostics. The Ioniq 5 and EV6 even display an estimated battery SOH in the infotainment system (look under EV settings, then battery information).

For deeper data, both Autel and LAUNCH scanners have decent Hyundai-Kia EV coverage, including cell group voltages and thermal data. OBDEleven is expanding support too. For most owners, the built-in battery health display combined with a standard OBD-II scanner for fault codes covers the basics.

Other Platforms (Brief Notes)

Renault Zoe / Megane E-Tech: CanZE (free Android app) provides battery data for Zoe. Coverage for the newer Megane E-Tech is still developing in the aftermarket tool space. BMW iX / i4 / iX3: BimmerCode and BimmerLink offer some EV-specific parameters. BMW's factory tool (ISTA) is available to enthusiasts through community channels, though the learning curve is steep. Peugeot e-208 / Opel Corsa-e (Stellantis): Largely locked-down for third-party tools. PSA-COM is the only real option and it's not beginner-friendly. If you're buying a used Stellantis EV, a dealer or specialist diagnostic session is your best bet.

EV Diagnostic Tools Comparison

Battery Health: What the Numbers Actually Mean

Battery health is the single most important metric for any EV, whether you're an owner watching degradation over time or a buyer evaluating a used car. Let's break down what the data means in practical terms.

State of Health (SOH)

SOH is the headline number: the percentage of original battery capacity remaining. A new EV starts at 100% (sometimes slightly above, as manufacturers build in a small buffer). Over time, capacity drops as the lithium-ion cells age through charge cycles, calendar ageing, and thermal stress.

What's normal? According to Geotab's 2025 study of over 22,000 EVs across multiple makes and models, the average degradation rate is approximately 2.3% per year. That's the global average. Some vehicles do better (Tesla Model 3 averages around 1.8% per year), some do worse (early Nissan Leafs without thermal management can hit 4-5% per year in warm climates).

Anything above 3-4% per year warrants investigation, especially if the car hasn't been heavily DC fast-charged. More than 20% total loss in five years is a red flag. Less than 15% loss in five years is solid.

The old version of this article said "10% loss in five years indicates a problem." That's wrong. 10% in five years is 2% per year, which is perfectly normal and actually slightly below the global average. Don't let outdated numbers scare you.

Cell Balance

A battery pack contains hundreds or thousands of individual cells grouped into modules. Cell balance tells you whether all those cells are ageing at the same rate.

A healthy pack shows cell voltages varying by only 10-20 mV when measured at the same state of charge. If one cell group is 50 mV or more below the others, that's a problem. The weak cells will continue diverging, the BMS will limit total pack capacity to protect the weakest link, and you'll see accelerating range loss.

Cell imbalance is one of the strongest predictors of future battery trouble. It's also one of the data points that only model-specific tools can show you.

Temperature Data

Lithium-ion cells degrade faster at temperature extremes. The thermal management system (liquid cooling on most modern EVs, air cooling on older Leafs and a few others) keeps the pack in its optimal range, typically 20-35°C during operation.

If your tool shows pack temperatures consistently above 40°C during normal driving, or large temperature differences between modules (say, 8°C+ spread), the thermal management system might be underperforming. Low coolant, a degraded pump, or a failing heat pump can all cause uneven heating, and the battery pays the price over time.

Battery Replacement Cost by EV Type (EU Market)

Costs include parts and labour. Refurbished packs can be 30-50% less. Most EVs carry 8-year/160,000 km battery warranties covering degradation below 70% SOH.

High-Voltage Safety: This Part Is Not Optional

EV battery packs operate at 400-800 volts. That voltage kills. Not "can be dangerous." Kills.

Under no circumstances should you open high-voltage battery enclosures, disconnect any orange-coloured cables or connectors, or attempt to service anything in the high-voltage circuit without proper training and insulated safety equipment rated for the voltage.

The capacitors in the inverter hold lethal charge even when the vehicle is completely powered off and the key is removed. They can retain dangerous voltage for minutes after shutdown. Professional EV technicians undergo dedicated high-voltage safety certification (in Europe, typically ECE R100 or equivalent national standards) before they're allowed to touch these systems. They use insulated gloves rated to 1,000V, insulated tools, and follow strict lockout procedures.

What you CAN safely do yourself:

• 12V battery replacement
• Tyre work, including rotation
• Cabin air filter replacement
• Brake fluid service
• Coolant level checks (on systems with accessible reservoirs)
• Wiper blades, bulbs, and cabin maintenance
• OBD-II diagnostics through the standard port
• Software updates through manufacturer apps

Everything involving orange cables, high-voltage labels, or the battery enclosure: leave it to the professionals. This isn't overcautious, this is basic electrical safety. High-voltage injuries cause severe burns, cardiac arrest, and death. Every year, there are incidents involving untrained people working on EV battery systems. Don't become one of them.

When to See a Professional (And How to Find One)

Some EV issues require specialist equipment and training regardless of what consumer tools you own.

Go to a professional for:

• Rapid range loss (more than 5-8% drop in a short period that isn't temperature-related)
• Battery or thermal management warning messages
• DC fast-charging speed dramatically reduced from baseline
• High-voltage isolation faults (these are serious and should not be driven on)
• Intermittent "turtle mode" or reduced power events
• 12V battery draining repeatedly (could indicate a parasitic draw from the HV system)
• Any collision damage near the battery enclosure, even minor

Finding an EV-capable independent shop in Europe:

The dealer isn't your only option, and EV-specialised independent shops are growing rapidly. In Germany, organisations like the ZDK (Zentralverband Deutsches Kraftfahrzeuggewerbe) maintain directories of EV-certified workshops. In the UK, the IMI (Institute of the Motor Industry) runs an EV technician certification programme with a public register. France has the GNFA certification. Most countries have equivalent programmes.

Ask specifically whether the shop has high-voltage safety certification, manufacturer-level scan tools (or at least professional multi-brand EV tools like Autel MaxiSys EV), and experience with your specific platform.

What to expect cost-wise: Professional EV diagnostic fees in Europe typically run €90-270 for a comprehensive evaluation, which includes battery health assessment, thermal system check, full module scan, and a written report. That's comparable to ICE diagnostic fees and well worth it when something seems off, considering what's at stake with battery pack values.

A Note on Right to Repair

The diagnostic tool gap on EVs isn't just a consumer inconvenience. It's becoming a policy issue. The EU's right-to-repair legislation (strengthened in 2024) aims to ensure that independent workshops and consumers have access to the same diagnostic data that dealers get. In practice, enforcement is uneven, and some manufacturers are better than others at providing open access.

This matters because the EV transition is creating a new generation of vehicles where the diagnostic data is more locked-down than ICE cars ever were. If you care about having choices for where you service your car (and not paying dealer-only prices for basic diagnostics), the right-to-repair movement is worth paying attention to. SpeakEV and r/electricvehicles have active threads tracking which manufacturers are cooperating and which are dragging their feet.

Closing Thoughts

The EV diagnostic tool landscape is messy right now. There's no single tool that does what a €30 Bluetooth adapter and a good app can do for a petrol car. Instead, you're dealing with a patchwork of model-specific solutions, locked-down manufacturer protocols, and a consumer tool market that's still catching up to the cars themselves.

But it's getting better. OBDEleven's EV coverage expands with every update. Autel and LAUNCH are adding new EV modules regularly. Community tools like LeafSpy and CanZE keep improving. And as the EU's right-to-repair framework gains teeth, manufacturers will face increasing pressure to open up diagnostic access.

In the meantime, know your tools. A generic OBD-II scanner still earns its keep on 12V monitoring and basic fault codes. Model-specific tools fill in the battery health gaps for the platforms that matter most.

The cars are brilliant. The tools will get there. We just need to push them along.

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Related: Tesla Error Codes: Complete Guide | Best Car Diagnostic Tools