Primary fault reference: SPN 168 FMI 1 — Full Fault Code Reference — This page covers the step-by-step repair workflow. For the complete fault definition, symptoms, causes, and derate risk, see the primary reference above.
Fix SPN 168 FMI 1 — Battery Voltage Below Normal
Battery, alternator, and charging system diagnosis
Overview
This fix guide covers the diagnosis and repair procedure for Fix SPN 168 FMI 1 — Battery Voltage Below Normal. Follow the steps below to identify the root cause and restore normal operation.
Safety Warnings
- ⚠Allow engine and exhaust to cool before working on related components.
- ⚠Disconnect battery before working on electrical circuits.
- ⚠Wear appropriate PPE — safety glasses, gloves, and hearing protection.
Step-by-Step Repair
Read all active fault codes
Connect OEM diagnostic software and document all active and inactive fault codes. Related faults must be diagnosed together.
Review live data
Monitor relevant live data parameters to identify the fault condition. Compare actual values to expected specifications.
Perform electrical tests
Test sensor or actuator circuits per the electrical test specifications for this fault code. Check reference voltage, ground, and signal circuits.
Inspect components
Physically inspect the sensor, actuator, wiring harness, and connectors for damage, corrosion, or contamination.
Replace faulty components
Replace the faulty sensor, actuator, or wiring as indicated by your diagnosis. Use OEM or equivalent quality parts.
Clear codes and verify
Clear all fault codes and perform a drive cycle or functional test to verify the repair. Confirm no fault codes return.
Verification Checklist
- No active fault codes after repair
- Live data parameters within normal range
- System operating normally under all load conditions