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SPN 168 FMI 15

Battery Potential / Power Input 1 — Value too high (least severe).
The reading is above normal, but only at the lowest warning level.

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

What FMI 15 usually points to: An early warning: mild over-temperature or over-pressure, or a sensor starting to drift high. More on FMI 15.

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 15 mean?

Battery Potential / Power Input 1 — value too high (least severe). The reading is above normal, but only at the lowest warning level.

Is SPN 168 FMI 15 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 15?

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