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SPN 520 FMI 2

Actual Retarder – Percent Torque — Data erratic, intermittent, or incorrect.
The signal jumps around, drops in and out, or disagrees with other information the controller has.

What the SPN covers: How much braking torque the retarder or engine brake is actually producing, as a percentage. More on SPN 520.

What FMI 2 usually points to: Loose or corroded connectors, chafed wiring, a failing sensor, or two redundant sensors that do not agree. More on FMI 2.

Severity

MEDIUM — fix soon

Your engine brake or retarder may not work. Drive with extra caution on grades.

Likely causes

  1. Retarder or engine brake control problem
  2. Network message missing or invalid
  3. Faulty retarder module or sensor

Checks & fixes (easiest first)

  1. Check retarder/engine brake operation and switch inputs
  2. Check for J1939 network codes
  3. Check codes in the retarder or transmission module

FAQ

What does SPN 520 FMI 2 mean?

Actual Retarder – Percent Torque — data erratic, intermittent, or incorrect. The signal jumps around, drops in and out, or disagrees with other information the controller has.

Is SPN 520 FMI 2 serious?

Your engine brake or retarder may not work. Drive with extra caution on grades.

What should I check first for SPN 520 FMI 2?

Check retarder/engine brake operation and switch inputs; Check for J1939 network codes; Check codes in the retarder or transmission module.