SPN 111 FMI 2 — Coolant Level Data Erratic
Erratic coolant level is volume proof plus header and sensor integrity first. Unnecessary cooling-system tear-downs for intermittent false low-level warnings is the most documented misdiagnosis.
Fault Overview
SPN 111 FMI 2 indicates the coolant level signal is unstable or implausible — an erratic or data-validity class fault. Failing level sensor, contaminated surge-tank header, intermittent harness, connector fretting, and actual intermittent aeration are the primary causes. Sensing issues are far more common than actual intermittent aeration — physical level verification is the required first step.
Engine & Platform Coverage
Possible Causes
- 1.Failing coolant level sensor with intermittent internal element
- 2.Contaminated surge-tank header producing unstable level readings
- 3.Connector fretting at coolant level sensor connector
- 4.Intermittent harness at flex points near surge tank
- 5.Actual intermittent aeration — less common than sensing issues
Wiring & Circuit Notes
Physical level verification is the required first step — confirm actual coolant volume before any electrical or pressure work. Inspect the surge-tank sensor connector for corrosion and harness flex points for intermittent continuity. Monitor PID stability parked and under load — electrical dropouts are abrupt.
DVOM Specs & Sensor Tests
Confirm physical coolant level first. Then monitor coolant level PID stability parked and under load. Abrupt electrical dropouts differ from gradual level changes from actual loss. Perform wiggle tests at the sensor connector and nearest harness flex points while monitoring the PID. Pressure-test the cooling system only if actual volume loss is confirmed after sensing is proven stable.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
6 steps locked behind Technician Mode- 1Verify physical coolant level — confirm actual volume before any electrical work
- 2Inspect surge-tank sensor connector for corrosion and harness flex points
- 3Monitor coolant level PID stability parked and under load
- 4Perform wiggle tests at sensor connector and nearest harness flex points
- 5Service connector and harness if intermittent source is identified
- 6Replace level sensor or header if sensing is unstable after connector service
- 7Pressure-test cooling system only if actual volume loss is confirmed
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
5 steps locked- 1Verify physical coolant level — confirm actual volume before any electrical work
- 2Inspect surge-tank sensor connector for corrosion and harness flex points
- 3Monitor coolant level PID stability parked and under load
- 4Perform wiggle tests at sensor connector and nearest harness flex points
- 5Service connector and harness if intermittent source is identified
- 6Replace level sensor or header if sensing is unstable after connector service
- 7Pressure-test cooling system only if actual volume loss is confirmed
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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Summary
SPN 111 FMI 2 is volume proof plus header and sensor integrity. Physical level must be confirmed before any pressure testing or cooling-system conclusions.