Grounds and bad earths
Starter turns slowly, lights behave strangely, multiple systems complain — yet every positive feed looks good.
What this lesson covers
CORE TEACHING Battery negative; chassis/body grounds; engine straps; ground points; corrosion; loose fasteners; shared grounds; why European brown wires are commonly ground but colour must never replace a diagram/test. PRACTICAL DEMONSTRATIONS AND TESTS Measure battery negative to engine block during crank; battery negative to body under load; inspect/clean strap; compare before and after. ADVANCED / SCAN TOOL LAYER Scope can later reveal ground offset/noise. Scan-module low-voltage codes can be tied back to shared grounding faults. KEY DIAGNOSTIC QUESTIONS Can current get back to battery negative? Is the ground good under load? Is one shared ground affecting several modules? MUST-COVER CHECKPOINTS Circuit must be loaded; positive side; ground side; connection-by-connection split; compare post-to-terminal; retest after repair.
What you will be able to do
Starter turns slowly, lights behave strangely, multiple systems complain — yet every positive feed looks good.
Where it sits in the programme
- Builds on
- Lesson 2: Voltage on a real vehicle
- Feeds into
- Lesson 4: Voltage-drop testing properly