Fuel Filter Restriction — Differential Pressure High / Supply Pressure Low
Fuel filter restriction is confirmed with differential pressure gauges. Inspect the element and supply system before repeating filter changes.
Fault Overview
Covers codes or data indicating fuel filter restriction — high differential pressure across the filter or low downstream pressure under load. The ECM or sensor detects restriction that limits fuel delivery.
Engine & Platform Coverage
Symptoms
- •Fuel filter restriction code
- •Plugged fuel filter indication
- •High fuel filter pressure differential
- •Low power with clean filters
- •Hard start with restricted filter
Possible Causes
- 1.Plugged primary or secondary fuel filter
- 2.Incorrect filter installed
- 3.Fuel contamination or algae growth
- 4.Waxing in cold weather
- 5.Collapsed filter element
- 6.Restriction in supply lines or tank pickup
Wiring & Circuit Notes
If a dedicated restriction switch or pressure sensor is used, inspect its connector and circuit for faults that could give false high readings.
DVOM Specs & Sensor Tests
Measure pressure before and after the filter under load or during a restriction test. Differential should remain within OEM limits. Restriction switch should open/close at specified pressure. Sensor voltage or data should correlate with mechanical gauge.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Step 1 — Install Mechanical Gauges: Install mechanical gauges before and after the filter if possible. This is the definitive test for actual restriction.
- 2Step 2 — Operate Under Load: Operate under load or perform OEM restriction test. Record differential pressure at idle and under load.
- 3Step 3 — Inspect Filter Element: Inspect filters for contamination type — water, debris, wax, algae. The contamination type identifies the source.
- 4Step 4 — Check Tank Pickup and Supply Lines: If filters are clean but restriction remains, check tank pickup and supply lines for restriction or collapse.
- 5Step 5 — Verify Sensor/Switch Circuit: If gauge data does not match scan data, verify the restriction sensor or switch circuit for false readings.
- 6Step 6 — Replace Filters and Retest: Replace filters and retest differential pressure. Confirm restriction is resolved before returning to service.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Replace primary and secondary filters $80–200; clean or replace tank pickup $100–300; address contamination source variable; repair sensor circuit $50–150. Total typical $80–350.
Start Diagnosing This Fault Now
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AI Diesel Tech — The Technician's Diagnostic Engine
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Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.