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MITO EV Auto L5 study materials
MITO EV Auto L5 study resources

MITO EV Auto L5: Automotive: High-Voltage EV Diagnosis and Repair

MITO EV Auto L5 · Work through your exam, one topic at a time.

All guide sections

Automotive: High-Voltage EV Diagnosis and Repair

What this domain tests

The Automotive domain of MITO EV Auto L5 tests safe diagnosis and repair of high-voltage (HV) electric vehicle systems. Expect questions on HV isolation, personal protective equipment, service disconnect, insulation testing, battery management system (BMS) data and fault tracing. The exam treats the HV battery and orange cables as live until you prove otherwise.

Core rules and concepts

  • Identify HV by orange cable/conduit and warning labels; never assume a vehicle is de-energised because the key is off.
  • Follow the manufacturer de-energisation sequence: key off, remove service disconnect or HV interlock, wait the specified discharge time, then verify absence of voltage at the test points with a CAT III meter rated for the pack voltage.
  • Use insulated tools, class 0 gloves with proof test, face shield and barriers. Lock out/tag out the service disconnect.
  • Insulation resistance is measured between the HV bus and chassis. Compare with service information, often expressed in Ω/V; a common specification is 500 Ω/V, but always use the OEM value.
  • BMS data includes state of charge (SoC), state of health (SoH), cell voltages, temperature and isolation fault status. A weak cell shows as a voltage delta under load.

Worked example

A 400 V pack has an isolation fault DTC. The service information specifies a minimum of 500 Ω/V. Expected minimum = 400 V × 500 Ω/V = 200 kΩ. You isolate the pack, wait, verify dead, then measure 80 kΩ from HV positive to chassis. 80 kΩ is below 200 kΩ, so the vehicle fails the isolation test. You do not re-energise. Next, disconnect HV components one at a time-PTC heater, compressor, charger-and retest to locate the low-resistance path.

Traps that cost marks

Using a CAT II multimeter; skipping the wait time; probing orange connectors with standard probes; treating a 12 V key-off as HV safe; replacing the battery without checking isolation; ignoring heater/chiller isolation faults; and failing to record the measurement conditions.