EV Won't Charge? Narrow It Down Before You Pay for Diagnosis

Who this affects

Universal triage rather than a model-specific defect. The order below runs cheapest and most common first, which is also the order a competent shop should work in.

The evidence

This page describes a diagnostic sequence rather than a single documented defect, so it carries no recall number. The ordering — 12V first, then the EVSE, then the port, then the on-board charger — reflects published guidance from EV diagnostic training and equipment sources, cited below. Where a specific model has a documented charging-related recall, that is covered on its own page and linked from here.

Likely causes

A weak or dead 12V auxiliary battery. The high-voltage system, including the on-board charger and battery management system, depends on the 12V for control power. If it is flat the car may not wake enough to initiate charging at all — dark dash, no charge-port light, apparently completely dead even with a charger plugged in.
The EVSE (the charging station or cable) rather than the car. Faulty units, tripped protection and damaged cables are common and are easy to rule out.
The charge port itself — a damaged connector, bent or corroded pins, a failed latch or a stuck port door. The port also carries pilot and proximity pins and an inlet temperature sensor, any of which can stop a session starting.
A failed on-board charger (OBC), which converts AC to DC. The tell is directional: if AC charging fails or is very slow but DC fast charging still works normally, the OBC is a prime suspect, because DC fast charging bypasses it.
A battery management system fault code withholding charge authorisation, or a fault in the high-voltage pack itself. These are the expensive end and should be the last conclusion, not the first.

How to tell them apart

A list of possible causes is only useful if you can narrow it down. These are the observations that discriminate — and they are the ones worth bringing to a shop.

Does it fail everywhere, or only at one charger? Try a different unit — ideally a different operator. A car that charges fine elsewhere has told you the problem was never the car.
Does AC fail while DC still works? That split points at the on-board charger, because DC fast charging bypasses it entirely. It is the single most useful observation you can make, and it costs nothing.
Does the car have 12V symptoms too — slow or dead infotainment, dim lights, a dashboard that will not wake? Then treat the 12V as the prime suspect rather than the charging hardware.
Look into the port with a torch before assuming anything electronic. Bent or corroded pins, or a latch that does not click, are visible and are more common than a failed on-board charger.
Does the session start and then stop within seconds, rather than never starting? That pattern more often points at a handshake or authorisation problem than at a physically broken component.

✅ Safe to check yourself

These leave the high-voltage system completely alone.

Test the 12V battery before anything else. It is the single most common cause and the cheapest fix, and skipping it is how people end up paying for HV diagnosis they never needed.
Try a different EVSE or public charger, and try your own EVSE on a different car if you can. This separates "the car will not charge" from "this charger will not charge".
Look into the charge port with a torch for bent, burnt or corroded pins, and for debris. Check the latch actually engages and the port door is not fouling.
Establish whether AC and DC behave differently. AC fails but DC works points at the on-board charger; both failing points elsewhere. This one observation saves a shop a lot of time.
Check for open recalls against your VIN before paying for anything.
Record the dash message verbatim, the charger type and power level, the ambient temperature and the state of charge. Charging faults are often intermittent and conditional.

⛔ Qualified technician only

Not a disclaimer — a genuine boundary. Knowing what sits on this side is also how you tell whether a quote is reasonable.

Opening, testing or replacing the on-board charger.
Any work on the high-voltage battery, its contactors or the junction box.
Reading and interpreting HV module fault codes, which are largely manufacturer-proprietary rather than standardised OBD-II — a generic scan tool will often show nothing useful.
All of the above require de-energisation, verified isolation, rated PPE and formal qualification.

Typical resolution

A 12V battery is an ordinary parts-and-labour job at any competent shop. An EVSE fault is a replacement, often under its own warranty. Charge-port damage ranges from cleaning to port replacement. An on-board charger is a significant component replacement and, on a car still in its warranty period, is exactly the kind of claim worth having service records for. Pack and BMS faults are dealer or HV-specialist territory.

What we could not verify

Failure-rate data by cause is not published in a form we can cite, so the ordering above reflects diagnostic guidance rather than measured frequency. Fault-code meanings vary by manufacturer and we are deliberately not publishing a generic EV DTC table, because most EV HV codes are proprietary and a generic table would be misleading.

Sources

Whatever the cause turns out to be, the thing that decides a warranty claim is usually evidence — a dated record of when the symptom started, the mileage, and the service history behind it. Intermittent faults get dismissed when an owner cannot demonstrate them. If you keep that record anywhere, keep it somewhere you will still have it in three years. Kotselog is a web app for exactly that: it logs services, mileage and fuel or charging so the history exists when you need it. It does not read fault codes or diagnose anything — that is what the shop and its tooling are for. Open the web app →

Other symptoms

← All EV problems & symptoms

EV won't charge: how to narrow it down