SPN 595 FMI 2 — Cruise Control Enable Switch Data Erratic
Erratic cruise enable data is usually an intermittent switch or conflicting interlock signal. Correlate all related inputs before replacing the switch.
Fault Overview
SPN 595 relates to cruise control enable or related switch status. FMI 2 indicates the data is erratic, intermittent, or implausible relative to other inputs (brake, clutch, vehicle speed).
Engine & Platform Coverage
Symptoms
- •Cruise control erratic
- •Cruise won't set
- •Cruise enable switch fault
- •Intermittent cruise
- •Cruise drops out
Possible Causes
- 1.Intermittent enable switch
- 2.Wiring chafe or loose connector
- 3.Brake or clutch switch interaction creating conflicting signals
- 4.Aftermarket switch or wiring
- 5.ECM input circuit noise
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Step 1 — Monitor Cruise Enable and All Interlock Statuses Simultaneously: Monitor cruise enable status and all related switches (brake, clutch, neutral) simultaneously in live data. Identify which input is creating the conflict.
- 2Step 2 — Perform Wiggle Test on Switch and Harness: Perform a wiggle test on the enable switch and harness while monitoring live data. Dropouts during wiggling confirm an intermittent connection.
- 3Step 3 — Measure Voltage Stability on Signal Circuit: Measure voltage on the signal circuit while operating the switch and wiggling the harness. Voltage dropouts confirm a wiring or connector issue.
- 4Step 4 — Check for Conflicting Interlock Signals: Verify brake, clutch, and neutral switch states are correct and not creating false inhibit signals that appear as erratic enable data.
- 5Step 5 — Isolate Aftermarket Devices: Disconnect any aftermarket cruise switches or devices and retest. Aftermarket installations frequently introduce noise or poor contact.
- 6Step 6 — Verify Vehicle Speed Signal Quality: Verify the vehicle speed signal is stable and within the range required for cruise enable.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Replace intermittent switch.
- 2Repair chafed wiring.
- 3Correct aftermarket installation.
- 4Clean or replace corroded connectors.
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.
Start Diagnosing This Fault Now
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Related Resources
Related Fault Codes
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Summary
Erratic cruise enable data is usually an intermittent switch or conflicting interlock signal. Correlate all related inputs before replacing the switch.