ELECTRICAL SUBSYSTEMe.g. SPN 100 FMI 4
Electrical Diagnostic Guide
Electrical system diagnostics — ground continuity, voltage drop, connector integrity, and harness inspection.
Common Symptoms
- 1Intermittent fault codes that clear themselves
- 2Multiple unrelated fault codes active
- 3Sensor reading erratic or out of range
- 4Ground continuity above 5Ω threshold
- 5Connector corrosion or pushed-back pins
- 6Voltage drop across power or ground circuit
Root Causes (Ranked by Frequency)
- High-resistance ground connection
- Corroded or damaged connector
- Chafed or shorted harness
- Pushed-back or spread connector pins
- Battery negative cable corrosion
- Missing or loose ground strap
Diagnostic Process — Step Preview
Structured diagnostic sequence — evidence-gated at each step
4 steps locked behind Technician Mode- 1INTAKE → fault code FMI classification
- 2SENSOR_VALIDATION → reference voltage check
- 3GROUND CONTINUITY GATE → ≤5Ω required
- 4ACTUATOR_TESTS → circuit resistance test
- 5VERIFICATION → voltage within spec post-repair
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