Check for no click when the relay is energized
Check for intermittent clicking or chattering
Check for burnt, melted, or discolored housing
Check for corrosion or loose terminals
Check for a broken or stuck armature
Measure coil resistance for open or shorted coil
Verify the coil gets the correct control voltage
Test continuity across the switched contacts
Check for high resistance or no continuity on closed contacts
Check for contacts stuck open or stuck closed
Check for excessive heat during operation
Swap with a known good relay to confirm failure