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EV & Hybrid Systems
The next 10 years of automotive work.
24 skill areas
60 key concepts
$0 to learn
EV & Hybrid Systems covers high-voltage safety, hybrid system diagnosis, and pure EV service. As of 2026 this is the fastest-growing service category and a durable differentiator. Everything below is free — no login, no paywall. Work through the skill areas, drill them in Study Mode, and when you're ready, prove it with the certification exam.
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What you'll be able to do
- High-voltage safety protocols: PPE, disable procedures, lockout
- Hybrid system architecture (parallel, series, series-parallel)
- Battery pack diagnosis at the module level
- DC-DC converter diagnosis
- Electric motor and inverter fundamentals
- EV-specific service: regenerative brakes, thermal management
- Level 2 charging equipment troubleshooting
- Common failure modes on Tesla, Nissan Leaf, Chevy Volt/Bolt, Rivian
Skill areas
Jump to any area — each one distills the concepts you need to master it.
Fundamentals
3 concepts- HEVs combine an ICE and electric drive. BEVs are pure electric with no combustion engine. PHEVs are HEVs with plug-in charging capability.
- Series hybrids (like Chevy Volt's early modes) have the engine as a generator only — never mechanically connected to the wheels. Common in EREVs.
- Parallel hybrids let both the ICE and motor drive the wheels via a shared transmission. Simpler than series but less flexible.
High Voltage
2 concepts- Prius Gen 2/3 traction battery is ~201-207V nominal (NiMH). Boost converters increase this to ~500-650V for the motor.
- BEV traction packs are 350-400V on most (Tesla Model 3, Bolt, Leaf). Newer 800V architectures (Porsche Taycan, GM Ultium, Hyundai E-GMP) improve fast-charging speeds.
Safety
6 concepts- Standard procedure: pull the service disconnect (loop or plug), wait the OE-specified interval (5-15 min), then verify 0V with a CAT III/IV meter at test points.
- Class 0 insulating gloves rated 1000V are the minimum. Must be inspected before use, air-tested, and within the 6-month test period.
- Orange is the universal color for HV. Never touch or cut orange-jacketed cables until de-energized and verified.
- Isolation is only proven by verified measurement. Use a CAT III/IV multimeter on a known-live source first to prove the meter works, then measure the target.
- Damaged HV packs can spontaneously ignite hours or days later. NFPA guidelines specify quarantine areas, water suppression, and awareness for towing/storage.
- Lithium fires are difficult. NFPA guidance is large water volumes to cool and drown. Reignition risk requires prolonged monitoring.
Cell Chemistry
3 concepts- Li-ion dominates: NCA (Tesla), NMC (many OEMs), LFP (cheaper, safer, longer-lived — increasingly common).
- LFP is thermally stable, cycles more times, but has lower energy density. Tesla, Ford, and others use LFP for standard-range packs.
- NCA offers high energy density but higher fire risk and higher cost. Tesla uses it extensively for long-range performance.
BMS
2 concepts- BMS is the pack's brain. It monitors every cell, balances them, manages thermal limits, and disconnects the pack if faults exceed safe limits.
- A pack's usable capacity is limited by the weakest cell. Imbalance causes early shutoff. BMS balances cells during charge to maximize usable capacity.
Cooling
3 concepts- Liquid cooling with coolant plates or channels handles the higher power densities of modern EVs. Air cooling only works for smaller packs (older Leaf).
- Pack coolant leaks can cause isolation faults. Use only OEM-approved coolant (some special dielectric formulas); improper coolant can conduct and short cells.
- Motor temp is monitored. Overheating triggers derating to protect windings. Verify pump operation and coolant flow, especially on repeated heavy loads.
Motor
4 concepts- PMSMs use rare-earth magnets for high efficiency; induction motors use squirrel-cage rotors. Some vehicles combine both (Tesla dual-motor).
- Regenerative braking runs the motor as a generator, converting motion back to electricity. Recaptures energy that would otherwise be lost to friction brakes.
- Dual-motor and quad-motor EVs can vary torque per motor precisely. Improves cornering, stability, and off-road capability without mechanical differentials.
- Regen recovers energy during deceleration. Efficiency depends on speed, battery temp, and available capacity.
Regenerative Braking
2 concepts- A full battery can't accept charge; a cold battery has restricted charge acceptance. Both reduce regen. Vehicle blends in friction brakes as needed.
- Regen does most braking. Brake pads on EVs can last 100k+ miles. Common issue: rusted rotors and pistons from disuse.
Inverter
2 concepts- Inverters bidirectionally convert between DC (battery) and AC (motor). Modern inverters use SiC (silicon carbide) semiconductors for efficiency.
- EVs still have 12V systems for lights, ECUs, and accessories. The DC-DC converter replaces the alternator, stepping HV to 12V continuously.
Charging
7 concepts- Level 1 uses 120V outlets. Slow (2-5 mi/hr). Level 2 is 240V (10-40 mi/hr). Level 3 is DC fast charging (100+ mi in 15 min).
- DC fast chargers do the AC-to-DC conversion externally, sending DC directly into the battery. Bypasses the onboard AC charger, allowing much higher power.
- Battery life is best when kept in the middle range. Frequent 0-100% cycles with high heat (fast charging) age cells faster.
- NACS (formerly Tesla connector) is being adopted by Ford, GM, Rivian, and most OEMs. Adapters bridge NACS and CCS. CHAdeMO is the older Japanese standard.
- Fast charging is heavily throttled if the pack is too hot or too cold. Communication faults between EVSE and vehicle also stop charging. Check pack temp and DTCs.
- OBC handles AC-to-DC for slower charging. Failure = no home charging. DC fast charging often still works. Confirm before replacing.
- EVSE is the charger box on the wall or in the ground. The actual charger (for AC charging) is onboard the vehicle. EVSE controls power delivery and safety.
Diagnostics
7 concepts- Isolation faults are dangerous because they can energize the chassis. HV systems monitor for isolation resistance continuously. Trace to component and repair.
- An insulation tester (megger) applies a controlled DC voltage (e.g., 500V) to measure resistance to chassis — detecting insulation degradation.
- HV connections have specific torque specs (both under- and over-torque are dangerous). Isolation test verifies no faults before re-energizing.
- Batteries degrade gradually. Most OEMs consider 20-30% capacity loss expected over 8-10 years. Measure SOH with a scan tool to confirm and compare to warranty threshold.
- HEVs favor engine-off when possible. Constant engine running suggests low SOC, faults, or cold-start warm-up cycles. Scan tool data confirms.
- P0AA6 is a hybrid isolation fault. Requires insulation resistance testing to trace the source. Do NOT operate the vehicle until resolved.
- Bent pins, damaged latch, or moisture in the charging port produces faults. Inspect visually before diving into pack diagnostics.
12V System
2 concepts- 12V wakes the vehicle's control system. Dead 12V = no HV enable. Jump-starting is fine (per OE), but the 12V battery must be diagnosed/replaced.
- Most EVs use AGM; some use small lithium 12V. Charged from the HV pack via DC-DC when vehicle is Ready. Some vehicles wake periodically to top off.
Motor Cooling
1 concept- High-performance motors often use oil directly on the windings (like Tesla Model Y). Others use liquid jackets. Motors that overheat lose power and self-limit.
Toyota Hybrid
3 concepts- THS uses the planetary gearset as an eCVT (electronic continuously variable transmission), splitting power between motor and engine electronically.
- Prius NiMH modules degrade over 150k+ miles or in high heat. Signs: reduced regen, ICE running more, battery light. Module replacement or full pack rebuild fixes it.
- P0A80 is a generic 'replace HV battery pack' code. Confirms battery degradation. In some markets, replacement modules or refurbished packs are common repairs.
Tesla
2 concepts- Tesla restricts most HV service to Tesla Service. Some independents specialize in Tesla, but access to service info and parts remains challenging.
- Early Model S drive units had gear noise and bearing failures. Later revisions improved this. Tesla-specialist rebuilders offer alternatives to full replacement.
Emissions
1 concept- HEVs/PHEVs still have emission requirements for their ICEs. States may have EV-specific fees (replacing gas tax revenue) or incentive requirements.
Regen
1 concept- Cold packs have restricted charge acceptance. Regen is reduced or disabled until the pack reaches operating temperature. Educate customers, don't misdiagnose.
HV Contactor
1 concept- Contactors are the pack's disconnect. Stuck open = no HV. Stuck closed = HV present when it shouldn't be — a safety hazard.
Heater
1 concept- Early EVs used resistive heaters (huge energy draw). Modern EVs increasingly use heat pumps (2-3x more efficient), leveraging the A/C circuit.
Range
2 concepts- Cold-weather range can drop 30-40%. Heat pump vehicles fare better. Pre-conditioning while plugged in preserves range.
- Pre-conditioning uses grid power for heat/cool. Saves battery for driving. Also warms battery for better regen and performance.
Regulation
2 concepts- State and federal incentives vary. Check current programs for tax credits, rebates, and HOV access — often expiring or changing yearly.
- OSHA 1910.269 electrical safety rules apply. Most OEs offer HV training with certification. ASE has EV/hybrid certifications. State licenses may apply for HVAC/HV work.
Tools
1 concept- CAT ratings define transient voltage protection. HV work requires CAT III (industrial) or CAT IV (utility) rated meters and leads. Lower-rated meters explode under fault conditions.
Range Test
1 concept- SOH tests read the BMS's calculated state, comparing to new pack capacity. Reveals cell-level imbalance or degradation and estimates remaining life.
Documentation
1 concept- HV work documentation supports safety, warranty, and liability. Detailed procedures protect the shop and technician if incidents occur later.
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