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SPN 168 FMI 1

Battery Potential / Power Input 1 — Value too low (most severe).
The reading is valid but far below the normal operating range, at the most serious 'too low' level.

What the SPN covers: Voltage the engine computer sees on its main power supply. More on SPN 168.

What FMI 1 usually points to: A real under-condition such as very low oil pressure or low fuel pressure, or a sensor that has drifted low. More on FMI 1.

Severity

MEDIUM — fix soon

Low or unstable voltage can cause many unrelated codes and no-starts. Fix power first.

Likely causes

  1. Weak batteries
  2. Loose or corroded battery cables
  3. Charging system fault (alternator)
  4. Bad ECM power or ground connection

Checks & fixes (easiest first)

  1. Load-test batteries
  2. Clean and tighten battery and ground cables
  3. Check charging voltage at the alternator and at the ECM
  4. Voltage-drop test the ECM power and ground circuits

FAQ

What does SPN 168 FMI 1 mean?

Battery Potential / Power Input 1 — value too low (most severe). The reading is valid but far below the normal operating range, at the most serious 'too low' level.

Is SPN 168 FMI 1 serious?

Low or unstable voltage can cause many unrelated codes and no-starts. Fix power first.

What should I check first for SPN 168 FMI 1?

Load-test batteries; Clean and tighten battery and ground cables; Check charging voltage at the alternator and at the ECM.