AI Diesel Tech
Proof in the Shop

Real Diagnoses.
Real Results.

See how AI Diesel Tech identified root causes faster, prevented unnecessary parts replacement, and saved shops real time and money.

Case Study 001

2019 Kenworth T680 — Cummins X15

SPN 3251 FMI 0 — DPF Differential Pressure High

~45 minutes saved

Problem

Truck entered the shop with a check engine light and a derate condition. The driver reported low power and increased fuel consumption over the past two weeks.

Symptoms

  • Active SPN 3251 FMI 0 — DPF differential pressure above threshold
  • Visible black smoke under load
  • Fuel economy down approximately 12% over 3 weeks
  • Regen cycles increasing in frequency

Tests Performed

  • DPF differential pressure sensor voltage check — within spec
  • DPF inlet and outlet pressure measurement at idle and under load
  • DPF visual inspection — heavy soot loading confirmed
  • Regen history review — 4 failed forced regens in past 30 days
  • Exhaust back pressure measurement — elevated at 8.2 inHg

Final Repair

DPF removed and sent for professional cleaning. Exhaust system inspected for restrictions. EGR cooler flow tested and found within spec. DPF reinstalled, forced regen completed successfully. Fault cleared, truck returned to service.

How AI Diesel Tech Helped

The FSM engine immediately flagged the failed regen history as the primary diagnostic path, bypassing the sensor voltage check that would have been the first step in a generic diagnostic flow. This saved approximately 45 minutes of unnecessary testing and correctly identified the DPF loading as the root cause rather than a sensor fault.

Time saved: ~45 minutesAvoided unnecessary DPF pressure sensor replacement ($180)

Case Study 002

2017 Peterbilt 579 — PACCAR MX-13

SPN 157 FMI 18 — Fuel Rail Pressure Low

~2 days of diagnostic time saved

Problem

Intermittent no-start condition reported by fleet manager. Truck would start normally on some attempts and crank without starting on others. No consistent pattern observed.

Symptoms

  • Intermittent no-start — cranks but does not fire
  • SPN 157 FMI 18 active during failed start attempts
  • Fuel rail pressure dropping below 200 bar during cranking
  • No active faults when truck starts normally

Tests Performed

  • Fuel rail pressure monitoring during multiple start attempts
  • Primary fuel filter restriction test — 22 psi restriction found (limit: 10 psi)
  • Secondary fuel filter restriction test — within spec
  • Lift pump output pressure test — 65 psi (within spec)
  • Fuel tank suction line inspection — no kinks or restrictions
  • High-pressure pump inlet pressure test — marginal at 45 psi

Final Repair

Primary fuel filter replaced. Secondary filter replaced as preventive maintenance. System primed and bled. Fuel rail pressure verified at 1,800 bar under load. Truck started on first attempt on 10 consecutive tests. Returned to fleet service.

How AI Diesel Tech Helped

The intermittent fault submodule activated immediately, adjusting the test sequence to capture data during both successful and failed start attempts. The engine identified the primary filter restriction as the root cause within 3 test steps — a diagnosis that had stumped the shop for two days because the filter appeared clean on visual inspection.

Time saved: ~2 days of diagnostic timeAvoided high-pressure pump replacement ($2,400 + labor)

Case Study 003

2021 Freightliner Cascadia — Detroit DD15

SPN 3936 FMI 2 — NOx Sensor Rationality

~3 hours saved

Problem

Truck in DEF/SCR derate with multiple active fault codes. Shop had already replaced the downstream NOx sensor twice with no resolution. Customer frustrated after $800 in parts with no fix.

Symptoms

  • SPN 3936 FMI 2 — downstream NOx sensor rationality fault
  • SPN 4364 FMI 18 — SCR NOx conversion efficiency low
  • DEF quality fault intermittently active
  • Truck in 5 mph derate

Tests Performed

  • DEF quality test — DEF concentration at 28% (spec: 32.5% ± 1.5%)
  • DEF tank drain and refill with verified DEF
  • SCR catalyst temperature monitoring during regen
  • Downstream NOx sensor voltage and response test
  • DEF dosing system flow rate test
  • DEF injector spray pattern inspection

Final Repair

DEF tank drained and refilled with fresh, verified DEF from a sealed container. DEF quality fault cleared. SCR efficiency monitored over 50-mile test drive — NOx conversion efficiency returned to 92%. All faults cleared. No sensor replacement required.

How AI Diesel Tech Helped

The multi-code cascade handler identified that the NOx sensor rationality fault was a downstream effect of the DEF quality issue — not a sensor failure. The engine's test sequence prioritized DEF quality verification before sensor testing, which the previous two repair attempts had skipped. This saved the customer a third unnecessary sensor replacement.

Time saved: ~3 hoursAvoided third NOx sensor replacement ($380 + labor)

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