Relay testing
Relay clicks, component still dead. Is the relay actually working?
What this lesson covers
CORE TEACHING Relay coil; magnetic field; contact resistance; 30/85/86/87/87a; normally open/closed; internal failure. Add suppression diodes/resistors across the coil, why some relays are polarity-sensitive, flyback voltage and why blindly swapping relays can be unsafe. PRACTICAL DEMONSTRATIONS AND TESTS Bench energise coil; continuity/contact-resistance test; voltage drop through loaded contacts; swap only when pinout/rating matches. Identify a diode-protected relay from its diagram and demonstrate correct coil polarity. ADVANCED / SCAN TOOL LAYER Scope relay command if ECU pulses it; show suppression diode/resistor considerations briefly. KEY DIAGNOSTIC QUESTIONS Does the coil energise? Do contacts close? Can contacts carry current under load? MUST-COVER CHECKPOINTS Identify 30/85/86/87/87a from diagram; coil test; control-side test; contact-side loaded test; socket terminal tension; suppression device.
What you will be able to do
Relay clicks, component still dead. Is the relay actually working?
Where it sits in the programme
- Builds on
- Lesson 13: Voltage drop across fuses and finding active circuits
- Feeds into
- Lesson 15: Testing the relay socket