Starter relay and start-control circuits
Starter itself is good, but the trigger terminal never receives 12 V.
What this lesson covers
CORE TEACHING Relay 30/85/86/87; coil vs contacts; ignition/start request; clutch/neutral switches; BCM/ECU control; immobiliser authorisation. PRACTICAL DEMONSTRATIONS AND TESTS Identify relay pins; test socket 30; test coil command/ground; bridge 30–87 only when circuit is understood and safe; check starter trigger. ADVANCED / SCAN TOOL LAYER Use scan tool to observe start request, clutch/neutral status and ECU output. Scope relay-control/PWM if relevant. KEY DIAGNOSTIC QUESTIONS Is the relay fed? Is its coil commanded? Does the contact close? Does output reach the starter? MUST-COVER CHECKPOINTS Separate control circuit from high-current circuit; prove battery first; B+ feed; trigger; positive drop; ground drop; current; mechanical result.
What you will be able to do
Starter itself is good, but the trigger terminal never receives 12 V.
Where it sits in the programme
- Builds on
- Lesson 7: Complete starter motor diagnosis
- Feeds into
- Lesson 9: Alternator testing properly