SPN 3512 FMI 3 — Aftertreatment DEF Pump Outlet Pressure Circuit Voltage Above Normal
DEF pump outlet pressure high-voltage codes are open-circuit electrical diagnostics first. DEF pump replaced because the outlet pressure circuit was open and the dosing strategy went irrational is the most documented misdiagnosis.
Fault Overview
SPN 3512 FMI 3 indicates the aftertreatment DEF pump outlet pressure sensor circuit voltage is above the normal maximum — an open circuit or high-signal class fault. Open signal wire, failed sensor, unplugged connector, and harness damage near the DEF pump are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Open signal wire from damage near DEF pump or module
- 2.Failed DEF pump outlet pressure sensor with internal open element
- 3.Unplugged connector after DEF system service
- 4.5V reference supply anomaly affecting sensor output
- 5.Damaged harness at DEF pump harness clamps
Wiring & Circuit Notes
Inspect the DEF pump outlet pressure sensor connector and harness near the DEF pump. Confirm connector is fully locked after any recent DEF system service. Verify 5V reference and ground at the sensor connector.
DVOM Specs & Sensor Tests
Confirm 5V reference and ground at the DEF pump outlet pressure sensor connector. An open circuit will not respond to actual pump pressure changes. DEF pump pressure evaluation is only appropriate after the sensor circuit is proven valid.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Confirm 5V reference and ground at DEF pump outlet pressure sensor connector
- 2Check signal wire continuity from sensor to ECM/dosing module
- 3Inspect connector for damage or loose lock — confirm fully locked after any recent DEF service
- 4Replace DEF pump outlet pressure sensor after circuit is proven clean
- 5DEF pump pressure evaluation only after sensing is confirmed valid
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Confirm 5V reference and ground at DEF pump outlet pressure sensor connector
- 2Check signal wire continuity from sensor to ECM/dosing module
- 3Inspect connector for damage or loose lock — confirm fully locked after any recent DEF service
- 4Replace DEF pump outlet pressure sensor after circuit is proven clean
- 5DEF pump pressure evaluation only after sensing is confirmed 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.
Start Diagnosing This Fault Now
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Summary
SPN 3512 FMI 3 is an open-circuit DEF pump outlet pressure diagnosis. The sensor circuit must be proven valid before any pump pressure or dosing conclusions are drawn.