xEV Diagnosis, Scan Tool Use, and Shop Safety Procedures
Scan tool capabilities
A capable scan tool reads HV battery data (state of charge, individual cell voltages, module temperatures, isolation resistance, contactor status), inverter and motor data, and OEM-specific DTCs with freeze frames. It may also command service mode, run active tests (contactor close, coolant pump), and perform battery/component initialization. Generic OBD-II typically will not display HV PIDs or support HV service functions.
Diagnostic approach
Start with the basics: a weak 12 V battery causes many false HV and communication faults. Record freeze frames and battery data before clearing codes. An isolation fault may originate in the pack, motor, A/C compressor, PTC heater, charger, or a chafed cable-use the OEM isolation test procedure and disconnect sections to isolate the branch. Do not clear codes to "see if it comes back" without documenting the original data.
Shop safety procedures
Work in a designated HV bay with barriers, warning signage, and locked access. Keep a fire extinguisher suitable for Li-ion fires and follow OEM emergency response guides; large volumes of water are often recommended to cool a thermal event, but only after de-energizing and with proper PPE. No metal tools on the pack, no sparks, no smoking, and no unqualified helpers in the area.
Traps
Using a non-OEM tool to disable HV; clearing codes and losing freeze frame; condemning a pack on one low cell reading without checking sense wiring; and forgetting to re-enable the HV system and clear the service mode before delivery.
Rule of thumb
Record first, clear last, and verify the repair with a road test and a full DTC scan.