PHEV Range Collapse in February

Most of it is explainable physics; the engine start is not yet explained.

Cabin heat: 4.8 kW from an 18.4 kWh pack is roughly 26% of nameplate capacity per hour. A 45-minute commute consumes about 3.6 kWh for heat alone - before traction. That is a large fraction of a 28 km display.

Cold pack: at 1 °C, available capacity is reduced (commonly 10–25% versus 25 °C) and internal resistance is up, which also cuts regenerative recovery. A display that adapts to recent consumption will show a big drop.

Degradation: 16.1 vs 16.9 kWh is about 5% - normal for the age.

The engine start at 60% SOC is not the temperature threshold, which is −10 °C and ambient is 2 °C. So find the actual reason from the engine-run-request data rather than guessing. Candidates: cabin heat request (many PHEVs fire the engine to make heat), battery warm-up strategy, catalyst or emissions maintenance, fuel/oil maintenance mode, or an HVAC fault forcing engine heat. Read the request-reason PID while reproducing the condition.

Collect:

• Cell voltage spread at rest and under load, and per-module temperatures versus ambient.
• AC energy in versus SOC change over a full charge - this is the number the learned capacity is derived from, and it is only meaningful with a temperature correction.
• Battery heater operation: commanded versus actual, coolant flow, and whether the heater valve is stuck. A pack that never warms charges slowly and shows poor cold range.
• Charge-time complaint history - long DC or AC sessions at low temperature support a heater problem rather than a capacity problem.
• Compare against the OEM's temperature-versus-available-capacity curve, or a like vehicle, rather than against the window sticker.

Justify replacement only if: voltage spread grows materially under load, measured capacity is well outside the temperature-corrected expectation, or there is an isolation/heater/coolant fault inside the pack. A 5% learned-capacity loss in winter is not a warranty pack.

Also rule out a calibration update or technical service bulletin for range estimation before promising anything - the display is an estimate, and fixing the estimate is not fixing the car.

Handle it as a documented, measured case rather than an argument.

1. Record ambient, pack temperature, heater draw, and the displayed range at arrival. Reproduce the engine-start condition and capture the request reason.
2. Run the temperature-corrected capacity check and put the number on the repair order next to the nameplate and the new-vehicle value.
3. Explain the mechanism in plain terms: cold pack holds less energy, cabin heat comes out of the same battery, and both effects are largest on short trips where the pack never warms.
4. Give him the levers he controls: precondition while plugged in, use seat heat instead of cabin heat where possible, and expect the display to recover in spring.
5. Only then, if the measured capacity still falls outside the OEM's criteria, submit the claim with the data attached.

Do not promise a pack, and do not dismiss him. If the engine is starting because of a heat-request strategy, that is worth showing him explicitly - it is the part of the complaint that feels like a defect and is actually a design choice.