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SPN 655 FMI 2

Injector Cylinder #05 — 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: Circuit or performance fault for the cylinder 5 fuel injector. More on SPN 655.

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

HIGH — limit use, diagnose now

Misfire and rough running are likely. Avoid heavy load; a stuck or leaking injector can wash down the cylinder or dilute the oil.

Likely causes

  1. Injector solenoid circuit open or shorted
  2. Chafed harness or loose terminal nut under the valve cover
  3. Worn, sticking or leaking injector
  4. Connector (feed) tube or seal problem
  5. ECM injector driver fault

Checks & fixes (easiest first)

  1. Check the FMI — open/short FMIs point to wiring and the coil first
  2. Read balance rates and run a cylinder cutout / contribution test
  3. Measure injector return flow, isolating cylinder 5 per the OEM procedure
  4. Inspect the harness under the valve cover and check oil level for fuel dilution

Troubleshooting guides

FAQ

What does SPN 655 FMI 2 mean?

Injector Cylinder #05 — data erratic, intermittent, or incorrect. The signal jumps around, drops in and out, or disagrees with other information the controller has.

Is SPN 655 FMI 2 serious?

Misfire and rough running are likely. Avoid heavy load; a stuck or leaking injector can wash down the cylinder or dilute the oil.

What should I check first for SPN 655 FMI 2?

Check the FMI — open/short FMIs point to wiring and the coil first; Read balance rates and run a cylinder cutout / contribution test; Measure injector return flow, isolating cylinder 5 per the OEM procedure.