SPN 1172 FMI 3 — Turbocharger Turbine Inlet Temperature Circuit Voltage Above Normal
Turbine inlet temp high-voltage codes are open-circuit heat-zone diagnostics first. Turbo or fueling work performed due to invalid turbine inlet temp data from an open circuit is the most documented misdiagnosis.
Fault Overview
SPN 1172 FMI 3 indicates the turbocharger turbine inlet temperature sensor circuit voltage is above the normal maximum — an open circuit or high-signal class fault. Open circuit, failed probe, unplugged connector, and heat-zone harness damage near the turbine housing are the primary causes. An open turbine inlet temp circuit typically reports an extreme cold value — correlate with manifold and EGT neighbors when available.
Engine & Platform Coverage
Possible Causes
- 1.Open circuit from brittle insulation failure near turbine housing
- 2.Failed turbine inlet EGT probe with internal open element
- 3.Unplugged connector after turbo or exhaust service
- 4.Burnt pins at connector near turbine housing
- 5.Clamp abrasion on heat sleeves near turbine inlet
Wiring & Circuit Notes
Inspect brittle insulation and burnt connectors near the turbine housing — heat-zone harness damage is the most common cause of SPN 1172 FMI 3. Correlate with manifold and EGT neighbor sensors when available to identify the dead sensor quickly.
DVOM Specs & Sensor Tests
Confirm 5V reference, ground, and signal at the turbine inlet temp sensor connector. An open circuit often reads extreme cold while neighbor sensors read plausible values. Replace the sensor and pigtail/harness after circuit is proven. Reassess high-load thermal behavior after sensing is valid.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Correlate turbine inlet temp PID with manifold and EGT neighbor sensors — extreme cold confirms open circuit
- 2Inspect connector for burnt pins and heat sleeve for abrasion damage near turbine housing
- 3Verify 5V reference and ground at turbine inlet temp sensor connector
- 4Check signal wire continuity from sensor to ECM
- 5Replace turbine inlet EGT sensor and pigtail/harness after circuit is proven
- 6Reassess high-load thermal behavior after sensing is valid
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
4 steps locked- 1Correlate turbine inlet temp PID with manifold and EGT neighbor sensors — extreme cold confirms open circuit
- 2Inspect connector for burnt pins and heat sleeve for abrasion damage near turbine housing
- 3Verify 5V reference and ground at turbine inlet temp sensor connector
- 4Check signal wire continuity from sensor to ECM
- 5Replace turbine inlet EGT sensor and pigtail/harness after circuit is proven
- 6Reassess high-load thermal behavior after sensing is valid
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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Common Symptoms
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Summary
SPN 1172 FMI 3 is an open-circuit turbine inlet temp diagnosis. The sensor circuit must be proven valid before any turbo or fueling thermal-path conclusions.