How do you troubleshoot 4-20 mA current loop problems?

4-20 mA troubleshooting: verify loop voltage (24 VDC supply, check at transmitter terminals), measure loop current (insert mA meter in series), check for shorts (current too high), check for opens (current zero or erratic), verify transmitter configuration (range, damping), check wiring (continuity, proper connections), and test with loop calibrator (source or simulate). Common problems: wrong range configuration, loose connections, water in junction boxes, and ground loops. Systematic approach: check from power supply through transmitter to input module. Document as-found and as-left readings.