Electric/Hybrid Vehicle System Repair and Replacement
This subtopic focuses on the safe repair and replacement of high-voltage systems in electric and hybrid vehicles, equipping technicians with the skills to follow manufacturer procedures, use specialist tools, and record work accurately. It ensures compliance with IMI Level 3 standards, preparing learners for real-world scenarios where safety and precision are paramount.
Assessment criteria
Topic Overview
The IMI Level 3 Technical Specialist in Electric/Hybrid Vehicle System Repair and Replacement (Award) is a specialised qualification designed for experienced technicians who want to advance their expertise in high-voltage (HV) vehicle systems. This award focuses on the safe diagnosis, repair, and replacement of electric and hybrid vehicle components, including HV batteries, electric drive motors, inverters, and charging systems. It goes beyond basic awareness, requiring a deep understanding of HV system architecture, energy management, and the use of diagnostic equipment to interpret live data from vehicle control units.
This qualification is critical as the automotive industry rapidly transitions to electrification. Technicians with this specialist status are in high demand to service and repair the growing fleet of electric vehicles (EVs) and plug-in hybrids (PHEVs). The course covers not only technical procedures but also the legislative and environmental considerations, such as the Waste Electrical and Electronic Equipment (WEEE) Directive and the End-of-Life Vehicles (ELV) Directive. Mastery of this content ensures you can work safely on HV systems up to 1,000 V AC or 1,500 V DC, complying with the Electricity at Work Regulations 1989 and IMI Code of Practice.
Within the wider Motor Vehicle & Transport sector, this award represents a key step towards becoming a Master Technician or a specialist EV/HV repair centre manager. It builds on Level 2 and 3 knowledge of conventional vehicles but shifts focus to the unique challenges of HV systems, such as capacitive discharge, thermal runaway risks, and the need for insulated tools and personal protective equipment (PPE). By the end of this award, you will be able to independently perform complex repairs like HV battery module replacement, inverter diagnostics, and motor drive testing, all while maintaining rigorous safety protocols.
Key Concepts
Core ideas you must understand for this topic
- →High-Voltage Safety Protocols: Understanding the five-step safety process – isolate, secure, prove dead, discharge, and test – using a voltage tester (e.g., Fluke 1587) and ensuring the vehicle is in a safe state before any work begins.
- →HV Battery Construction and Management: Knowledge of lithium-ion (Li-ion) and nickel-metal hydride (NiMH) battery chemistries, cell balancing, battery management system (BMS) functions, and thermal management systems (active cooling/heating).
- →Electric Drive Systems: How the electric motor (e.g., permanent magnet synchronous motor) and inverter work together to convert DC from the battery to AC for the motor, including regenerative braking and torque vectoring.
- →Charging Systems and Infrastructure: Differences between AC (Mode 2/3) and DC (Mode 4) charging, onboard charger operation, CHAdeMO vs. CCS standards, and the impact of charging speed on battery health.
- →Diagnostic Techniques: Using manufacturer-specific diagnostic tools (e.g., BMW ISTA, Tesla Toolbox) to read HV system fault codes, interpret live data (e.g., battery voltage, insulation resistance), and perform actuator tests on contactors and coolant pumps.
Learning Objectives
What you need to know and understand
- 1. Be able to work safely on an electric/hybrid vehicle2. Be able to use information to carry out the task3. Be able to use appropriate tools and equipment4. Know how to carry out repairs on high energy electrical systems5. Be able to carry out repairs on high energy electrical systems6. Be able to record information and make suitable recommendations
Assessment Criteria
Key criteria assessors look for in your portfolio
- Award credit for thorough risk assessment including isolation of high-voltage system and use of appropriate PPE before starting work.
- Expect evidence of correctly interpreting vehicle technical data, wiring diagrams, and repair instructions.
- Require demonstration of proper tool selection and usage, such as insulated tools and testing equipment, with calibration checks.
- Look for a systematic approach to diagnosing and repairing high energy systems, including post-repair functional tests.
- Assess ability to complete repair records clearly, noting measurements, repairs performed, and parts replaced, with recommendations for future maintenance.
Assessment Guidance
Guidance for achieving higher grades
- 💡Always start by referencing the specific vehicle safety guide and follow the manufacturer's isolation procedure step by step.
- 💡Practice using manufacturer diagnostic tools and interpreting live data to strengthen your fault-finding skills.
- 💡Document all actions contemporaneously in the logbook to ensure accurate records for assessment.
- 💡Prepare a personal checklist of PPE and tool requirements before each repair task to avoid omissions.
- 💡When answering questions about HV safety, always reference the specific regulations (e.g., Electricity at Work Regulations 1989) and the IMI Code of Practice. Examiners look for evidence that you understand the legal framework, not just the practical steps. For example, state that you must 'isolate the HV system using the service disconnect and then lock-off/tag-out (LOTO) according to your employer's procedures.'
- 💡For diagnostic questions, demonstrate a systematic approach: start by gathering customer concerns, then use a diagnostic flow chart to isolate the fault. Mention specific tools like a megohmmeter for insulation testing or a thermal imaging camera for identifying hot spots in battery packs. Avoid vague statements like 'check the battery'; instead, say 'perform a capacity test on the HV battery using a diagnostic tool to compare state of health (SOH) against manufacturer specifications.'
- 💡In written answers, use correct terminology: 'traction battery' not 'main battery', 'inverter' not 'converter', 'contactors' not 'relays'. Also, show awareness of different EV architectures (e.g., series hybrid vs. parallel hybrid) and how they affect repair procedures. For example, a series hybrid may have a smaller engine but a larger generator, affecting the cooling system layout.
Common Mistakes
Common errors to avoid in your coursework
- Failing to verify the vehicle is fully powered down and capacitors discharged before beginning repairs.
- Misinterpreting wiring diagrams, leading to incorrect component replacement.
- Using non-insulated tools or attempting repairs without proper isolation procedures.
- Neglecting to torque high-voltage connections to manufacturer specifications.
- Providing vague or incomplete repair records, missing essential diagnostic data.
- Misconception: 'Once the HV system is isolated, it's safe to touch any component.' Correction: Even after isolation, capacitors in the inverter and DC-DC converter can hold a lethal charge for several minutes. Always follow the manufacturer's specified discharge time and use a voltage tester to confirm zero voltage before touching any orange cables or components.
- Misconception: 'A hybrid vehicle's HV battery is the same as a standard 12V battery.' Correction: HV batteries operate at 200-800V and contain hundreds of cells. They require specialised handling, including the use of insulated tools (rated for at least 1,000V), HV gloves (Class 0), and a fire extinguisher rated for lithium-ion fires (e.g., Class D or water mist). Never short-circuit an HV battery terminal.
- Misconception: 'Regenerative braking means the brake pads never wear out.' Correction: While regen reduces brake pad wear, the friction brakes are still used, especially at low speeds or during emergency stops. The brake system must still be serviced according to the manufacturer's schedule, and the regen system can affect brake pedal feel, requiring specific bleeding procedures.
Frequently Asked Questions
Common questions students ask about this topic
Pass / Merit / Distinction Evidence Checklist
How your portfolio evidence is graded for THE INSTITUTE OF THE MOTOR INDUSTRY Electric/Hybrid Vehicle System Repair and Replacement
Every vocational unit is marked against named criteria rather than an exam percentage. Your tutor's brief lists the exact codes for this unit — here is what each band is asking you to do.
Demonstrate baseline knowledge, accurate terminology, and core practical application.
Provide detailed analysis, structured explanations, and clear workplace reasoning.
Deliver thorough evaluation, original problem solving, and fully justified recommendations.
Before You Start
Prior knowledge that will help with this topic
- •A solid understanding of Level 2 and 3 automotive principles, including 12V electrical systems, basic engine operation, and vehicle mechanical systems. You should be comfortable using multimeters, oscilloscopes, and diagnostic software.
- •Completion of an IMI Level 3 Award in Electric/Hybrid Vehicle System Repair and Replacement (or equivalent) that covers the safe isolation and basic maintenance of HV systems. This specialist award builds on that foundation with advanced diagnostics and component-level repair.
- •Practical experience working on live HV systems under supervision, including the use of HV PPE and insulated tools. You should have a current IMI TechSafe registration or equivalent evidence of competency in HV safety.
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Key Terminology
Essential terms to know
- 1. Be able to work safely on an electric/hybrid vehicle2. Be able to use information to carry out the task3. Be able to use appropriate tools and equipment4. Know how to carry out repairs on high energy electrical systems5. Be able to carry out repairs on high energy electrical systems6. Be able to record information and make suitable recommendations
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