SPN 3511 FMI 2 — Sensor Supply Voltage 2 Data Erratic
Erratic Supply 2 is bank-specific isolation under vibration and load. Technicians replacing Supply 1 sensors by mistake during a Supply 2 intermittent event is the most documented pattern on this fault class.
Fault Overview
SPN 3511 FMI 2 indicates sensor supply bank 2 is unstable or implausible. Intermittent short on a Supply 2 sensor, fretting connector on that bank, moisture intrusion, and a failing supply driver are the primary causes. Bank-specific isolation prevents cross-bank parts replacement.
Engine & Platform Coverage
Symptoms
- •Supply 2 bank sensors dropping out together intermittently
- •Vref 2 unstable under vibration
- •Supply 1 remains stable while Supply 2 collapses
- •Bank 2 sensor codes that come and go with vibration
- •Intermittent fueling or boost errors from Supply 2 sensors
Possible Causes
- 1.Intermittent short on a Supply 2 sensor collapsing the bank under vibration
- 2.Fretting connector on Supply 2 branch
- 3.Moisture intrusion at a Supply 2 branch connector
- 4.Failing ECM supply driver for bank 2 — less common
- 5.Chafed harness on Supply 2 routing
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Single Action Gate — Graph Both Supply Banks: Connect a scan tool or DVOM to monitor both Supply 1 and Supply 2 voltages simultaneously. Graph both banks while operating the vehicle or duplicating the conditions that trigger the fault. If Supply 2 collapses under vibration and Supply 1 stays stable, the fault is bank-2 specific.
- 2Binary Decision Gate — Wiggle-Isolate Supply 2 Branches: While graphing Supply 2, wiggle and flex each Supply 2 branch harness individually. If Supply 2 collapses only when a specific branch is disturbed, that branch contains the fault. Narrow to the smallest harness section.
- 3Override Manager — Repair Offender: Repair the identified intermittent shorted sensor, fretting connector, or chafed harness on Supply 2. Confirm Supply 2 stabilizes after repair before reconnecting all other Supply 2 loads.
- 4Safety Interceptor — Confirm Bank Stability and Code Cleanup: After repair, verify Supply 2 is stable under all operating conditions including vibration. Confirm all related Supply 2 sensor codes clear. Verify Supply 1 was not affected.
- 5Resume Point — ECM Only If Supply Remains Unstable With Loads Removed: Proceed to ECM diagnosis only if Supply 2 remains unstable with all sensor loads removed and power/grounds are confirmed perfect. This confirms the ECM supply driver is the source.
- 6Verification Loop — Post-Repair Supply Confirmation: After repair, verify Supply 2 is stable under vibration and all operating conditions. Confirm all related codes remain clear over extended operation.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Repair intermittent shorted sensor at identified Supply 2 branch.
- 2Repair fretting connector at identified Supply 2 branch location.
- 3Repair chafed harness at identified Supply 2 flex point.
- 4Replace ECM only if Supply 2 remains unstable with all loads removed and power/grounds are perfect.
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 3511 FMI 2 is a bank-specific isolation diagnosis. Erratic Supply 2 requires graphing both banks simultaneously, wiggle-isolating Supply 2 branches, and repairing the offender before any ECM replacement.