SPN 3511 FMI 3 — Sensor Supply Voltage 2 Above Normal
Supply 2 high is a bank isolation and intrusion diagnosis. Mis-pinned connectors after repairs feeding battery voltage into one reference bank is the most documented pattern on this fault class.
Fault Overview
SPN 3511 FMI 3 indicates sensor supply bank 2 voltage is above the maximum threshold. Short to higher voltage on the Supply 2 branch, failed supply regulator, and miswire after service are the primary causes. Bank intrusion isolation is required before ECM replacement due to high risk of sensor damage on the elevated bank.
Engine & Platform Coverage
Symptoms
- •Multiple Supply 2 sensor FMI 3 high-voltage codes active
- •Supply 2 voltage above OEM reference
- •Supply 1 remains healthy
- •Bank-specific high-voltage cascade
- •Sensor damage after recent harness repair near Supply 2
Possible Causes
- 1.Short to battery or ignition voltage on Supply 2 branch
- 2.Failed ECM supply regulator for bank 2 — less common
- 3.Mis-pinned connector after harness repair feeding battery voltage into Supply 2
- 4.Backfeed from a damaged sensor on Supply 2 bus
- 5.Jump-start miswire event affecting Supply 2 circuit
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Single Action Gate — Identify Supply 2 Sensors: Map which sensors are on Supply 2 using OEM wiring diagrams. Measure Supply 2 voltage at the ECM reference output and at a known Supply 2 sensor. Compare to Supply 1 voltage. A high Supply 2 with normal Supply 1 confirms a bank-specific condition.
- 2Binary Decision Gate — Measure Voltage and Isolate Branch: Disconnect Supply 2 sensors one branch at a time. Recheck Supply 2 voltage after each disconnection. If voltage drops to normal after disconnecting one branch, that branch contains the intrusion source.
- 3Override Manager — Repair Short or Miswire: Inspect the identified branch for mis-pinned connectors, battery or ignition voltage intrusion, and damaged sensors. Repair the short or miswire before reconnecting any Supply 2 loads.
- 4Safety Interceptor — ECM Only If Unloaded Supply Still Incorrect: Proceed to ECM diagnosis only if the unloaded Supply 2 voltage remains above normal with all sensor loads disconnected and power/grounds are confirmed good. This confirms the ECM internal regulator is the source.
- 5Verification Loop — Post-Repair Supply Confirmation: After repair, verify Supply 2 is within OEM specification. Confirm Supply 1 remains healthy. Verify all related sensor codes clear. Inspect for sensor damage if elevated Supply 2 was sustained.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Repair mis-pinned connector or harness miswire at identified Supply 2 branch.
- 2Repair backfeeding sensor or harness branch.
- 3Replace damaged sensors if elevated Supply 2 caused sensor damage.
- 4Replace ECM only if unloaded Supply 2 remains high with proven good power and grounds.
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 3511 FMI 3 (Sensor Supply Voltage 2) is a bank intrusion and isolation diagnosis. High Supply 2 requires measuring the bank, isolating branches, and repairing the voltage intrusion source before any ECM replacement.