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HEV and PHEV systems DR vs MG (2025): technical comparison, HV safety and diagnosis

Understanding how a hybrid manages energy is the key to repairing it effectively. In this guide, I compare the logic of HEV (full hybrid) and PHEV (plug-in hybrid) hybrid systems from the DR and MG brands, with a workshop perspective: architectures, high-voltage safety, vehicle networks, and practical diagnostic procedures. It's the same approach I adopt in the classroom when I train technicians on HEV/PHEV platforms imported into Europe.

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HEV vs. PHEV: Differences That Matter in the Workshop

HEVs and PHEVs share key components (HV battery, inverter, electric motor(s), gearbox, OBC/DC-DC in PHEVs), but differ profoundly:

• Available energy : PHEVs have larger batteries (higher kWh) and an On-Board Charger (OBC) for charging from the mains.
• Driving modes : HEVs optimised for automatic hybridisation; PHEVs offer pure EV, hybrid and active charging (charge/sustain).
• Maintenance and diagnosis : OBC, battery thermal management and charging connectivity (socket, relays, contactors) come into play on PHEVs.

For the auto repairer, the difference translates into specific procedures on HV, thermal management, and energy efficiency tests (braking regeneration, ICE-assist strategies, etc.).

Read Also: HV BATTERY COOLING SYSTEMS – DIFFERENCES BETWEEN HEV AND PHEV AND THERMAL FAULT DIAGNOSIS (2026)

Hybrid DR Platforms: What to Expect

The Chinese-derived DR platforms bring HEV/PHEV systems to Europe with a pragmatic approach: parallel/power-split architectures, compact HV modules, and CAN vehicle networks with gateways. In the workshop, this means:

• Modular diagnosis on inverter, reducer and battery pack with focus on contactors , HV sensors and cell balancing .
• Practical procedures for safety and recovery, with attention to the orange connectors and capacitor discharge time.
• Sometimes documentation is sparse: it is advisable to create internal cards with “good” values ​​detected in the workshop (current/voltage patterns).

MG Hybrid Platforms: Strengths and Cons

MG solutions stand out for their integration and quality of control strategies. Shopfloor users appreciate:

• Effective energy management (smooth ICE/EV transitions), with predictable PWM duties and frequencies on EGR/fans/control valves.
• Well-structured diagnostic interfaces (UDS on CAN) and consistent DTC logic.
• Caution : always check the battery/inverter cooling loop and the status of the insulation control (HVIL, sensors and wiring).

Architectures and networks: power-split, parallel, CAN/LIN

Typical architectures

• Parallel : ICE and electric motor act together on the drive axle; simple, efficient in constant motion.
• Power-split : intelligent power distribution with gears/planetary gears; excellent for urban use and transients.
• Series (extended hybrid) : ICE as generator; the axle is driven only by the e-motor (rarer in platforms treated in traditional workshops).

Vehicle networks (traction)

• CAN HS for powertrain and HV (hybrid ECU, BMS, inverter, OBC, DC-DC).
• CAN MS/LS and LIN for body and thermal (pumps, valves, fans, HVAC).
• Central gateway with security and message filtering functions between domains.

HV Safety: PPE, Lockout/Tagout and Securing

Working on HV requires specific disciplines . Maintain a standardized protocol:

1. PPE : certified insulating gloves, visor, insulating mat, suitable footwear.
2. Lockout/Tagout : Disconnects HV service/disconnect key, isolates 12V, applies security tag.
3. Discharge capacitors : respect the required times (minutes), then check for the absence of voltage with an approved instrument.
4. Work area : surround the vehicle, no liquids, isolated tools, informed assistant.
5. Reset : Recheck HVIL, tightening torques and log on hybrid ECU before starting.

Guided diagnosis: flows, measures and tools

Basic flow (valid for DR and MG)

1. Pre-check 12V : voltage, drops, battery condition. A weak 12V will cause strange codes on the HV.
2. Full DTC scan : powertrain, hybrid, BMS, thermal, body/gateway.
3. Live key data : State of Charge (SoC), battery/inverter/OBC temperatures, HV insulation, contactor status.
4. Actuator testing : HV coolant pumps, valves, fans, charging relays (PHEV).
5. Electrical measurements : ripple on DC-DC, drops during hybrid start-up, PWM duty for thermal control.
6. Instrumented road test : check EV/HEV transitions, regeneration, ICE/e-motor torque consistency.

Recommended tools

• OBD II/UDS diagnosis with special functions for hybrids (battery bleed loop, HV measurement, contactor test).
• Oscilloscope (4 channels): signal synchronization (e.g. PWM pumps, contactor controls), DC-DC/OBC ripple.
• Clamp meter and suitable CAT TRMS multimeter .
• Thermal imaging camera for hot-spots on inverters, OBCs, electric compressors and HV connectors.

Read Also: OSCILLOSCOPE - COMPLETE GUIDE: SETTINGS, CONNECTIONS, MEASUREMENT STRATEGIES AND REAL-WORLD CASES

Real recurring cases

1) PHEV: AC charging that stops

• Symptoms : Charging starts/stops, irregular timing.
• Probable causes : OBC overheated, cooling fan/pump, EVSE contact (socket), relay.
• Approach : OBC log, cooling actuator test, thermography, contact verification and socket communication protocol.

2) HEV: EV mode not available

• Symptoms : ECU in sustain , ICE always on.
• Causes : Low SoC, battery temp out of range, HVIL not perfect, inconsistent pedal/brake sensors.
• Approach : Live SoC/Temp data, sensor tests, adaptive resets, and road tests.

3) HV insulation alarm

• Symptoms : warning light, reduced power, DTC isolation.
• Causes : Moisture in connectors, damaged cables, faulty insulation sensor.
• Approach : Check orange connectors, measure with dedicated instrument, dry/recondition connectors.

Quick table: HEV vs PHEV in the workshop

Voice	HEV (DR/MG)	PHEV (DR/MG)	Workshop notes
HV Battery	Medium-low capacity	High capacity (kWh)	Always check SoC and cooling
Charging from the mains	No OBC	OBC 1-/3.3-/7.4 kW typical	EVSE Test and Connectors
EV Strategies	EV limited/assist	Pure EV + hybrid + charge	Check enabling conditions
Extra diagnosis	BMS/basic inverter	OBC, HV contactors, insulation	Add thermal tests

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