SPN 2630 FMI 4 — Charge Air Cooler Outlet Temperature Circuit Voltage Below Normal
CAC outlet temp low-voltage codes need short isolation before cooler work. False hot charge-air conclusions from shorted outlet temp sensors leading to unnecessary CAC replacement is the most documented misdiagnosis.
Fault Overview
SPN 2630 FMI 4 indicates the charge air cooler outlet temperature sensor circuit voltage is below the normal minimum — a short circuit or low-signal class fault. Signal short to ground, failed sensor with internal short, crushed harness at charge pipe clamp edges, and moisture bridging are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Signal wire short to ground at clamp edges on charge pipes or CAC end-tank areas
- 2.Failed CAC outlet temp sensor with internal short to ground
- 3.Crushed harness at charge pipe clamp edge
- 4.Moisture bridging at connector body near CAC outlet
- 5.Insulation damage from abrasion at charge pipe clamps
Wiring & Circuit Notes
Inspect clamp edges on charge pipes and cooler end-tank areas — these are the highest-probability short locations for the CAC outlet temp circuit. Check for moisture in the connector body.
DVOM Specs & Sensor Tests
Disconnect the CAC outlet temp sensor and check the signal wire for short to ground. If the short clears with the sensor disconnected, the sensor is internally shorted. If the short persists, inspect the harness at charge pipe clamp edges. After repair, compare CAC outlet temp to ambient and IAT under load — values should rise in a plausible way.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Disconnect CAC outlet temp sensor connector
- 2Check signal wire for short to ground with sensor disconnected
- 3If short clears with sensor disconnected, replace sensor
- 4If short persists, inspect harness at charge pipe clamp edges
- 5Repair harness short at identified location
- 6Evaluate true CAC efficiency only if temperature remains high after circuit is clean
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
4 steps locked- 1Disconnect CAC outlet temp sensor connector
- 2Check signal wire for short to ground with sensor disconnected
- 3If short clears with sensor disconnected, replace sensor
- 4If short persists, inspect harness at charge pipe clamp edges
- 5Repair harness short at identified location
- 6Evaluate true CAC efficiency only if temperature remains high after circuit is clean
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 2630 FMI 4 requires short isolation before any CAC efficiency or cooler-package work. The sensor circuit must be proven valid first.