EV Charger Fault Codes and Fault Families

Insulation fault (IMD trip)

The insulation monitoring device watches resistance from DC positive and DC negative to protective earth and trips when it falls below roughly 100 ohms per volt, about 100 kilohms on a 1000 volt system.

Isolation or insulation fault code at session start or once current flows

Session terminates within seconds of the cable check or precharge stage

Fault clears in dry weather and returns after rain

Moisture in a conduit body, fitting, or the dispenser cable vault

A stray copper strand touching a grounded enclosure or terminal plate

Damaged or pinched output cable insulation

Capacitive leakage from a long run of shielded DC cable

Failed surge protection device leaking to ground

Treat the fault as a live ground fault until proven otherwise

Isolate, lock out, verify absence of voltage, and allow DC link capacitors to discharge

Megger DC positive to PE and DC negative to PE at the dispenser and at the cabinet; compare against the manufacturer threshold

Open and inspect the lowest conduit bodies and fittings for water

Inspect terminations for stray strands and creepage paths

If readings float with cable length and weather, suspect capacitive leakage and consult the manufacturer

STOP WORK posture. This is a possible energized ground fault on high voltage DC. Isolate and verify before touching conductors. Only a qualified person proceeds.

UL 2231

NFPA 70E 130.4

IEC 61851 protection requirements

True

Personnel ground fault protection trip (CCID)

AC side charging circuit interrupting devices per UL 2231 trip on milliamp scale leakage to protect people. Frequent trips mean real leakage somewhere downstream, not a nuisance to bypass.

Charging stops with a ground fault or CCID code on an AC station

Trips repeat with a specific vehicle or in wet weather

Trips immediately on plug in before any current flows

Moisture in the connector holster or cable

Damaged cable jacket leaking to ground

Vehicle onboard charger leakage

Miswired neutral or ground bond downstream of the device

Never bypass or jumper a personnel protection device

Retest per the manufacturer test procedure and record the trip

Dry and inspect the connector and cable, then retest

Try a known good vehicle to split vehicle versus station

Verify grounding and bonding continuity back to the source

The device is doing its job. Find the leakage path. Bypassing personnel protection is prohibited.

UL 2231

NEC 625.54 GFCI requirements

SAE J1772

True

DC contactor fault

Output contactors switch the DC bus to the cable. Loose secondary wiring, feedback line issues, or terminal problems cause erratic behavior; frequent cycling under load welds or burns contacts.

Contactor feedback or mirror contact fault codes

Loud chatter or repeated clicking at session start

Session blocked at cable check even though the vehicle is healthy

Charger reports an output voltage with the session off, a welded contact signature

Loose coil secondary wiring or connector vibration

Feedback or auxiliary contact circuit fault

Welded main contacts from cycling under load or high inrush

Burned or pitted contacts near end of life

Coil driver board failure

Isolate, lock out, verify absence of voltage, and wait out DC link discharge before opening the contactor box

Check coil connections, secondary wiring, and feedback wiring torque

Measure contact resistance and compare poles

Verify the mirror contact state matches the main contacts in both positions

A welded contactor means the cable can be live when it should be dead. Treat the whole output as energized until proven otherwise

A welded contactor can leave the connector energized. Verify absence of voltage at the connector pins before handling.

Manufacturer service manual

NFPA 70E 120.5 verification

True

Precharge circuit fault

Before the main contactors close, a precharge resistor path brings the cable and vehicle side up to match the DC link so the contacts do not close across a large voltage difference. A failed precharge blocks every session at the same early stage.

Every session fails at the same point right after cable check

Precharge timeout or voltage mismatch fault codes

Audible click sequence stops before the main contactor thunk

Open or drifted precharge resistor

Failed precharge relay or its driver

Voltage sense divider fault reporting a false mismatch

Vehicle refusing because measured voltage differs from announced voltage

Isolate, lock out, verify absence of voltage, and allow capacitor discharge

Measure the precharge resistor against its rating

Verify the precharge relay coil and contacts

Cross check both voltage sense chains against a trusted meter reading

Watch the handshake log for the voltage the vehicle reports versus what the charger measures

DC link capacitors hold charge after isolation. Verify discharge before touching the precharge circuit.

Manufacturer service manual

NFPA 70E stored energy provisions

True

Power module fault or derate

DC fast chargers stack rectifier and converter modules. A failed module usually removes a slice of output power rather than killing the unit, so the classic signature is a charger that works but caps well below nameplate.

Output caps at a fraction of nameplate, for example 100 kW from a 150 kW unit

Module communication loss or module over temperature codes

One module fan bank silent while the others run

Failed rectifier or DC converter module

Module internal fan or blocked module airflow

Module comm bus wiring or termination fault

AC input phase loss reducing module capacity

Read the per module status page before opening anything

Verify all three input phases and phase to phase voltages

Isolate and lock out before module extraction, then follow the manufacturer swap procedure

Check module bus connectors and seating

After replacement confirm firmware compatibility across modules

Modules hold stored energy and are heavy. Isolate first, use the documented extraction procedure, and mind lifting.

Manufacturer service manual

True

AC input problem

Phase loss, undervoltage, or upstream protection issues starve the whole unit. The charger may boot on control power yet refuse sessions or derate heavily.

Input undervoltage, phase loss, or phase rotation codes

Charger boots but refuses every session regardless of vehicle

Breaker or fused disconnect found tripped or single phasing

Utility side sag or lost phase

Tripped upstream breaker or blown fuse on one phase

Loose lugs heating and dropping a phase under load

Incorrect rotation after upstream electrical work

Measure all three phases at the input terminals, phase to phase and phase to ground

Thermal scan lugs and terminations under load if possible

Verify rotation with a phase rotation meter after any upstream work

Inspect and torque terminations to specification with the circuit isolated

Input work is energized electrical work until isolated and verified. Follow the energized work permit process if isolation is impossible.

NFPA 70E 130

NEC 110.14 terminations

False

Vehicle handshake failure (CCS or NACS)

The pilot goes to state C but the high level handshake dies before energy flows. This localizes the problem to the charger to vehicle link: pilot wiring, PLC comms, the connector, contactors, precharge, or ISO 15118 certificates.

Session ends during SLAC, cable check, or precharge

Works with some vehicle makes and fails with others

Vehicle shows a charging error while the backend shows the charger online and idle

Stuck or damaged DC contactor blocking cable check

Precharge fault causing a voltage mismatch abort

Faulty charge port or connector temperature sensor ending the session

Comms or PLC modem board fault

ISO 15118 Plug and Charge certificate problem, expired or wrong chain

Worn connector pins or a damaged pilot line in the cable

Confirm the backend link is up; a live backend with a dying session points at the vehicle side

Read the stage where the handshake stops from the session log; each stage names its subsystem

Try a known good vehicle or a CCS test rig to split vehicle versus charger

Check pilot voltage and PWM at the connector against the J1772 table

Inspect connector pins and the cable for damage and heat marks

If only Plug and Charge sessions fail, fall back to RFID and flag certificates

Follow isolation practice before touching the connector internals; a welded contactor can leave pins live.

SAE J1772

ISO 15118

IEC 61851

DIN SPEC 70121

True

Control pilot fault

The 1 kHz plus and minus 12 volt pilot line is the heartbeat of every AC session and the front door of every DC session. Wrong voltage levels, a failed diode check, or a broken pilot conductor stop everything before it starts.

No response at plug in, as if nothing is connected

Pilot or diode check fault codes

Intermittent session drops when the cable is moved

Broken pilot conductor inside a flexed or crushed cable

Worn pilot pin not making contact

Vehicle inlet damage or a failed vehicle diode

Pilot board failure on the charger side

Wrong proximity resistor reading from a damaged latch

Measure pilot voltage at the connector: near 12 V standby, 9 V connected, 6 V charging per the J1772 ladder

Verify PWM duty cycle matches the advertised current

Wiggle test the cable while watching the pilot to catch intermittents

Inspect the pilot and proximity pins under magnification

Swap test with a known good cable or vehicle when available

Pilot circuits are low voltage but live in an energized cabinet. Keep clear of the power terminals while probing.

SAE J1772

IEC 61851 Annex A

False

Thermal derate or termination

A session that starts clean and dies after a few percent, or output that tapers far below nameplate on a hot day, points to a thermal limit: cable cooling, connector temperature, module airflow, or a real insulation issue that only crosses threshold once current flows.

Session terminates a few percent in, repeatably

Output tapers hard in hot weather or after back to back sessions

Connector or cable warm to the touch beyond normal

Coolant level or pump fault codes on liquid cooled units

Low coolant, failed pump, or air in a liquid cooled cable loop

Blocked intake filters or failed cabinet fans

Worn connector contacts heating under current

Charge port or cable temperature sensor drift

An insulation fault that only appears at current, mimicking thermal

Pull the temperature telemetry for the failed sessions before touching hardware

Inspect coolant level, pump operation, and loop pressure on liquid cooled cables

Check filters, fans, and airflow paths

Thermal scan the connector and cable during a supervised session

If temperatures look normal but sessions still die under load, pivot to the insulation fault family

Hot connectors and cables can burn. Let hardware cool before handling and never defeat a temperature interlock.

Manufacturer service manual

UL 2202 temperature provisions

True

Connector and cable wear

Public connectors take thousands of drops, drive overs, and yanks. Worn contacts raise resistance and heat; damaged latches break proximity detection; crushed cables break pilot and comm lines.

Sessions only start when the connector is held or wiggled

Heat discoloration on the connector face or pins

Latch does not click or the release button sticks

Repeated user complaints on one dispenser while its twin runs fine

Worn or spread power contacts

Broken latch spring changing the proximity resistance

Cable crushed by vehicles driving over it

Holster damage letting water into the connector

Liquid cooled cable jacket damage and coolant weep

Inspect pins for wear, spread, heat color, and debris

Verify proximity resistance through the latch positions

Flex the cable along its length feeling for crush points while watching pilot continuity

Compare contact resistance against a healthy twin dispenser

Replace as an assembly per manufacturer procedure; connector rebuilds in the field rarely hold

Verify the output is dead before pin level inspection. A welded contactor upstream can keep pins live.

SAE J1772

Manufacturer cable and connector service bulletin

True

Backend or network failure

The charger is healthy but cannot reach or hold its OCPP backend: authorization times out, sessions never start for app users, or the station shows offline to the network while lights are on locally.

App or RFID authorization spins and times out

Station shows offline in the network portal while powered locally

Sessions start with a local card whitelist but not from the app

OCPP boot notification loops or websocket reconnect cycling

Cellular signal degradation or a failed antenna connection

SIM deactivated, data plan lapsed, or APN change

Backend URL or certificate change after a network migration

Firewall or carrier NAT closing the websocket

Backend outage at the charge point operator

Check signal strength and the modem status page first

Verify the backend URL, charge point id, and OCPP version against the network record

Watch for a boot notification acknowledgment in the local log

Power cycle the router or modem once, not repeatedly

Confirm whether the operator allows offline authorization; the charger may accept a cached whitelist while disconnected

Call the network operations center with the charge point id before replacing hardware

Network faults are not electrical hazards by themselves, but never leave a charger energized with protection features disabled while troubleshooting comms.

OCPP 1.6

OCPP 2.0.1

Operator network requirements

True