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SPN 84 FMI 10

Wheel-Based Vehicle Speed — Abnormal rate of change.
The value is changing faster than is physically believable.

What the SPN covers: Vehicle road speed calculated from a wheel or output-shaft speed signal. More on SPN 84.

What FMI 10 usually points to: Intermittent wiring, a sensor glitch, or a sudden real event such as a burst hose. More on FMI 10.

Severity

MEDIUM — fix soon

Speedometer, cruise and speed limiting may misbehave. Safe to move carefully to a shop.

Likely causes

  1. Damaged or dirty vehicle speed sensor
  2. Wrong sensor air gap or damaged tone ring
  3. Wiring damage
  4. Incorrect tire size or axle ratio programmed

Checks & fixes (easiest first)

  1. Inspect the speed sensor and tone ring for debris and damage
  2. Measure sensor resistance and AC output while turning
  3. Check the parameter programming for tire revs/mile and axle ratio
  4. Look for ABS codes that point to the same sensor

FAQ

What does SPN 84 FMI 10 mean?

Wheel-Based Vehicle Speed — abnormal rate of change. The value is changing faster than is physically believable.

Is SPN 84 FMI 10 serious?

Speedometer, cruise and speed limiting may misbehave. Safe to move carefully to a shop.

What should I check first for SPN 84 FMI 10?

Inspect the speed sensor and tone ring for debris and damage; Measure sensor resistance and AC output while turning; Check the parameter programming for tire revs/mile and axle ratio.