ISO 15118 explained: how your EV and charger talk through the cable

Published 06/11/2026 · By Voldt® product team

ISO 15118 is the standard that lets an electric car and a charger exchange data through the charging cable. It uses the same thin signal wire that every Type 2 charge already relies on. DC rapid charging can’t work without it, although UK rules don’t require it.

The narrowest part sets the flow

Cable

rated 32 A

Charge point

offers 16 A

Car

accepts 32 A

16 A

Charging runs at the lowest limit: 16 A, about 11 kW on three phases.

Every Type 2 plug has two small signal pins next to the big power pins. Even without ISO 15118, the charger and the car use one of them, the Control Pilot (CP), to talk in a very simple way. The charger sends a fast on-off signal, and the length of each “on” tells the car how much current it may take. The car answers by changing the voltage when it’s ready to charge.

ISO 15118 adds a second, much richer conversation on the same wire. Small modems in the car and the charger send data at a far higher frequency than the on-off signal, so the two don’t get in each other’s way. The basic signal can only say how much current is available. A very short pulse of 5% is the charger’s signal to start this data link. With ISO 15118, the car and charger can agree on limits, share the battery level and plan the charge around your departure time. The 2022 version, ISO 15118-20, adds charging in both directions.

A charging cable has no chip or electronics inside, but it still tells the charger something important. Each plug has a small resistor on the Proximity Pilot (PP) pin, and the charger measures it the moment you plug in. Each value stands for a rating: 1,5 kΩ means 13 A, 680 Ω means 20 A, 220 Ω means 32 A and 100 Ω means 63 A (IEC 61851-1). The charger never sends more current than that rating allows.

Apart from that, the cable simply passes the signals along, unchanged. That makes the two signal pins the part to look after: they’re the smallest contacts in the plug, so water, dirt or a bent pin can stop a charge before it starts. Voldt® plug housings are moulded in one piece, with silver-plated copper pins.

With AC charging, the car’s built-in charger turns the power into what the battery needs, so the charge point only has to say how much current is available. With DC rapid charging, that conversion happens inside the rapid charger and the power goes straight into the battery. The car has to ask for an exact voltage and current and keep adjusting as the battery fills. An on-off signal can’t carry that, so every CCS rapid charge uses ISO 15118 or its older German version, DIN SPEC 70121.

Before any power flows, the charger checks that its cable is safe and matches its voltage to the battery. When the charge ends, the car checks that its own power switches have opened before it releases the plug. The cable on a rapid charger is tethered to it, so your own cable plays no part here.

If nothing happens when you plug in, the car isn’t getting a clean signal from the small pins. Look at both ends of the cable for water, dirt, or a bent or blackened pin. Dry them and plug in again. Push each plug in all the way: a charge point with a socket locks the plug before it switches on, and a plug that isn’t fully in won’t lock.

An adapter adds extra contacts the signal has to pass through, so leave it out if you can. If a different cable works on the same charge point, the first cable is the problem, and one with a damaged pin should be replaced. If neither works, the fault lies with the charge point or the car, and the operator or your garage can check the error log.

Home and workplace chargers sold in Great Britain since 30 June 2022 must be smart under the Electric Vehicles (Smart Charge Points) Regulations 2021. They have to keep working if you switch energy supplier, charge off-peak by default and add a short random delay before starting, so that not every car on the street starts at once. Public chargers follow the Public Charge Point Regulations 2023: contactless payment on new chargers of 8 kW and up, 99% reliability on rapid networks and prices shown in pence per kWh.

The EU has gone further: from 1 January 2027, new wallboxes and public chargers there must support ISO 15118-20 (Delegated Regulation (EU) 2025/656). In the UK it’s a feature to look for on the spec sheet, and rapid chargers use it or DIN SPEC 70121 anyway.

• Push both plugs fully home and wait for them to lock.
• Stop using a cable with cracked insulation, bent pins or scorch marks.
• Where your car’s manual differs from this guide, follow the manual.

Voldt® cables and portable chargers are UKCA and CE marked and TÜV certified, with a 3-year warranty. Terms and exclusions are on the warranty and complaints page.