SPN 558 FMI 2 — Accelerator Pedal / Idle Validation Data Erratic
Idle validation erratic faults are correlation diagnostics between switch or logic state and APP. Limp mode from intermittent idle validation disagreement — when the switch or wiring was the cause — is the most documented pattern.
Fault Overview
SPN 558 FMI 2 indicates idle validation or related APP validation data is erratic or implausible. Failing validation switch, APP correlation issues, harness intermittents, and misadjusted pedal stops where applicable are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Failing idle validation switch with intermittent contact
- 2.APP correlation issues producing disagreement at rest and tip-in
- 3.Harness intermittents at pedal assembly connector
- 4.Misadjusted pedal stops affecting validation window
- 5.Water intrusion at validation switch or pedal connector
Wiring & Circuit Notes
Monitor APP and validation state together at rest and through tip-in transitions. Unstable transitions at rest or first-travel positions indicate switch or wiring issues. Circuit wiggle tests at the pedal assembly connector and validation switch wiring.
DVOM Specs & Sensor Tests
Monitor APP and validation state simultaneously at rest and through tip-in. At rest and first-travel positions, validation state should match APP. Unstable transitions indicate switch or wiring issues. Circuit wiggle tests at pedal connector. Adjust or replace pedal components after proof.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Monitor APP and validation state simultaneously at rest and tip-in
- 2Check rest and first-travel transition stability
- 3Circuit wiggle tests at pedal assembly connector and validation switch
- 4Check pedal stop adjustment per OEM specification where applicable
- 5Replace validation switch or pedal assembly after proof
- 6Verify stable transitions at rest and tip-in after repair
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
4 steps locked- 1Monitor APP and validation state simultaneously at rest and tip-in
- 2Check rest and first-travel transition stability
- 3Circuit wiggle tests at pedal assembly connector and validation switch
- 4Check pedal stop adjustment per OEM specification where applicable
- 5Replace validation switch or pedal assembly after proof
- 6Verify stable transitions at rest and tip-in after repair
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
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Related Resources
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Summary
SPN 558 FMI 2 is a correlation diagnostic between validation switch state and APP. Switch and circuit proof are required before any module conclusions.