Diagnostic Case Study

Degraded Pack, Dead Module Sensors & Warm A/C

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A 2020 Jaguar I-Pace EV (185k km) presented with a range complaint and an A/C that stopped getting cold. There were no warning lights or obvious DTCs on the dash.

The Challenge

This was a complex case featuring one component telling three connected stories. We had a degraded HV pack whose thermal sensing was compromised, on a car whose A/C shares the battery's refrigerant loop. Standard fault codes didn't reveal any of it.

To solve it, the workshop had to correlate live OBD channels across the thermal management systems.

Structuring the Diagnostic

By adopting a structured and documented approach, the workshop used the EVMetricsOBD Workshop Templates to guide the diagnostic process. These templates lead the technician through a strict hierarchy of tests, ruling out causes logically and preventing expensive misdiagnoses.

EV HV Battery Recall & Thermal Integrity

Correlate pack health, per-module thermal sensing and the shared cooling loop — for degraded packs, recall checks, and EV A/C-won't-cool complaints
  • Recall / TSB check
    Verify the VIN against open HV-battery recalls (e.g. I-Pace LG-cell fire risk) and record the current BMS software level
  • Capacity vs Power Health
    Read both from the BMS. Capacity fade with full power and tight cells = uniformly aged pack, not a single weak cell
  • Cell voltage spread
    Confirm highest-vs-lowest cell is within spec; a wide spread points at a failing cell rather than even aging
  • Module temp sensor sanity
    Compare every per-module temperature against pack Min/Avg/Max; flag any stuck/floor (e.g. −15 °C in a warm pack) or flapping channels as failed thermistors
  • HV isolation / sense rails
    Check the BECM HV-sense voltages are steady and consistent; intermittent 0↔400 V flapping indicates an isolation or sense-wiring fault
  • Battery chiller & cooling loop
    Confirm the refrigerant/coolant loop is cold AND that cooling actually reaches the pack; check the chiller and expansion/thermal-management valve
  • Cabin-cool cross-check
    If the A/C won't cool but the refrigerant line is cold, suspect the shared battery-chiller valving or air-side distribution before any regas. Mark N/A if there's no A/C complaint.
  • Gate: HV De-energization
    Before any module or pack work, complete the HV System De-energization protocol (PPE, isolation, capacitor bleed, zero-volt verification)
The Outcome The structured approach exposed a battery pack with uniform aging and failing thermistors, perfectly matching a known recall profile. Because the A/C loop is shared with the battery chiller, diagnosing the thermal side explained the cabin symptoms without a pointless A/C regas. The owner got a data-backed reason to push for a warranty/recall assessment.