Theory and operation
Auxiliary feedback may report mechanical position while voltage comparison detects welded or failed-open contacts; a pyrofuse is normally a one-time crash device.
Battery & High Voltage / Diagnostic guide
CONTACTORS, PRECHARGE & PYROFUSE.
Interpret positive, negative, precharge and crash-disconnect devices as one controlled sequence.
EV GUIDE10/24
Use this guide to organize evidence. Vehicle-specific high-voltage access, measurements and component isolation require OEM procedures, appropriate qualifications, rated PPE and approved test equipment.
GUIDE PURPOSE
Diagnose the system—not one isolated value.
Confirm vehicle state, operating conditions and the full DTC record before clearing evidence or opening the high-voltage system.
Diagnostic evidence
Graph pack voltage, DC-link voltage, coil command, auxiliary feedback, precharge time and crash/isolation permissions together.
Safe diagnostic path
Confirm the exact sequence, then decide whether the failure is permission, coil/control, contact resistance, precharge path or downstream load.
Boundary and common error
Do not command contactors repeatedly into an unresolved short or bypass a pyrofuse.
Specifications, connector access, disable sequences, wait times and allowable tests vary by model and voltage architecture.