How to Use the AI Diesel Tech Diagnostic Engine
Everything you need to get from fault code to confirmed root cause — fast. Read this before your first session or keep it open as a reference.
Important — Read Before Every Session
- AI Diesel Tech is a diagnostic aid — not a substitute for qualified technician judgment.
- All repair procedures must be verified against OEM service manuals before execution.
- Never perform electrical tests on live circuits without proper PPE and training.
- Voltage, resistance, and pressure values provided are reference ranges — actual specs vary by engine serial number, calibration, and operating conditions.
- AI Diesel Tech is not liable for misdiagnosis, vehicle damage, or personal injury resulting from use of this platform.
- By using this platform you confirm you are a trained technician or working under qualified supervision.
The disclaimer modal appears at the start of every new session. You must click "I Agree & Continue" before the diagnostic engine activates. A persistent reminder banner remains visible throughout your session.
The User Manual button in the disclaimer modal links directly to this page — so you can review it before agreeing.
AI Diesel Tech is a professional-grade AI diagnostic platform built specifically for heavy-duty diesel technicians. It combines a structured finite state machine (FSM) with a large language model trained on J1939, OBD-II, and OEM service data to guide you through a systematic, test-family-based diagnostic process.
Phase 2 FSM v7.0
VIN-aware, multi-code, test-family-based diagnostic orchestration with cheapest-first test ordering.
Tech Mode
Unlocks DVOM voltages, PSI/ohm specs, pinout data, and OEM-level procedures for subscribers.
Reference Panel
Auto-populated wiring diagrams, procedures, fault data, and technician notes — all in one panel.
Extended Reference
Expanded multi-circuit sensor value tables to confirm good vs. bad readings across systems.
Quick Reference Bar
Instant access to +/−/Ground/Ω definitions, test methods, and expected values.
Dark / Light Mode
Full dark and light theme support — toggle anytime from the toolbar.
- DieselVision™ photo accuracy system — multimodal photo-based mechanical assistance
- Technician Chat™ multimodal photo input — snap a photo and get an instant answer
- Phase 2 FSM v7.0 — faster test-family selection and improved code clustering
- Improved wiring diagram auto-fetch — more SPN/FMI coverage
- Extended Reference sensor value tables — expanded system coverage
- Faster cascade-code clustering — root-cause identification in fewer steps
The Start Diagnosis form is your launchpad. The more information you enter here, the faster and more accurate the AI's first response will be. Every field feeds directly into the Phase 2 FSM vehicle profile.
Enter VIN (optional but recommended)
The VIN unlocks VIN-aware diagnostics — the FSM uses it to resolve engine family, fuel system type, induction type, and emissions tier automatically. Without a VIN, you can still diagnose but must select fields manually.
Year, Make, Model
Enter the vehicle year, manufacturer (e.g. Freightliner, Kenworth, Peterbilt), and model (e.g. Cascadia, T680, 579). This builds the vehicle profile used throughout the session.
Select Engine Platform
Choose from the dropdown — grouped by OEM (Cummins, Detroit Diesel, PACCAR, Volvo, International, CAT). Selecting the correct engine platform gives the AI access to platform-specific fault data, threshold values, and test families.
Always select the engine platform. It is the single biggest factor in diagnostic accuracy.
Vehicle Mode — Diesel or Auto
Toggle between Diesel (J1939 / heavy-duty) and Auto (OBD-II / light-duty). This switches the fault code format and the underlying knowledge base.
Primary Fault Code
Enter the fault code that triggered the diagnosis. For J1939 use SPN/FMI format (e.g. 3719 31). For OBD-II use the standard code (e.g. P0171).
Related / Cascade Codes
Add any other active codes that appeared at the same time. The Phase 2 FSM uses code clustering to identify root-cause relationships between codes — entering cascade codes dramatically improves the diagnostic path.
Enter all active codes, not just the one you think is the problem. The FSM may identify a master code driving multiple symptoms.
Pro Tips for the Start Form
- Include mileage and recent repairs in the first chat message
- Note whether the code is active, pending, or historical
- Mention any derate level (25%, 5 mph, shutdown)
- Describe symptoms — smoke color, noise, power loss
- The more detail you provide, the faster we can fix it
Once you submit the start form, you land in the diagnostic chat session. The AI acts as your AI diesel technician — asking targeted questions, ordering tests cheapest-first, and building toward a confirmed root cause.
Answer every question completely
The FSM advances states based on your answers. Vague answers like "it seems low" slow the process. Give exact readings: "fuel rail pressure reads 18,500 PSI at idle, drops to 14,200 under load."
Provide test results as you go
When the AI asks you to perform a DVOM test, do it and report the exact value. The FSM uses real measurements to confirm or rule out fault paths.
Sessions are saved automatically
Your session is saved with a unique ID. You can close the browser and resume later — the full conversation, reference panel, and FSM state are preserved.
The more details you provide upfront, the faster we can fix it. A complete first message can skip 3–4 back-and-forth questions.
Tech Mode is the subscriber-only layer that unlocks the full depth of the diagnostic engine. Toggle it with the Tech Mode button in the chat toolbar.
Tech Mode OFF
- • Symptoms and root cause overview
- • General repair guidance
- • Severity and derate information
- • Component location descriptions
Tech Mode ON (Subscribers)
- • DVOM voltage specs (V, mV)
- • Pressure specs (PSI, bar, kPa)
- • Resistance values (Ω, kΩ)
- • Connector pinout data
- • OEM-level test procedures
- • Wiring diagram references
The Tech Mode toggle is visible in the top toolbar of the chat session. When active, a green indicator confirms it is on. The v7.0 badge next to it confirms you are running the latest Phase 2 FSM model.
The Phase 2 Finite State Machine (FSM) v7.0 is the intelligence layer that drives every diagnostic session. It wraps the Phase 1 base FSM and adds VIN-aware, multi-code, test-family-based orchestration.
How it works
Flagship Diagnostic Flows
P0171 NAVacuumLeakFamily → AirflowFamily → FuelDeliveryFamilyP0171 TurboBoostTurboFamily → FuelDeliveryFamily → AirflowFamilyP0420ExhaustO2Family → SensorSanityFamilySPN 3719AftertreatmentFamily → BoostTurboFamily → SensorSanityFamilyIf the FSM returns INCONCLUSIVE, provide more test data. Conflicting readings usually mean a wiring fault — check for intermittent opens and high-resistance connections.
The chat toolbar runs across the top of the session and gives you quick access to all session controls.
The Quick Reference Bar is the thin bar at the bottom of the chat panel. It gives instant access to the four core electrical measurement concepts every diesel tech needs at their fingertips.
Tap any icon to expand a popup with the full definition, how-to-test instructions, common failures, and expected values for that measurement type.
The Reference Panel is the right-side panel in the split-screen layout. It auto-populates as the AI pushes reference data during the session — wiring diagrams, procedures, fault data, and more.
Wiring diagrams are automatically fetched and pushed to the Reference Panel when the AI identifies the active SPN/FMI. You can also upload your own diagrams directly in the session.
Auto-fetch
When a primary fault code is entered, the system queries the wiring diagram database for matching SPN/FMI. Available diagrams appear in the Wiring tab of the Reference Panel automatically.
Upload your own
Use the wiring diagram upload button in the chat toolbar to add your own diagrams — OEM PDFs, photos of schematics, or annotated images. Uploaded diagrams are stored with the session.
Lightbox view
Click any diagram thumbnail to open it in full-screen lightbox mode for detailed inspection. Pinch-to-zoom is supported on mobile.
If no diagram auto-loads, upload a photo of the relevant circuit from your OEM service manual. The AI can reference uploaded diagrams in its analysis.
The Extended Reference panel is an expanded version of the Quick Reference Bar. Where the Quick Ref gives you the four core measurement types, the Extended Reference gives you a full multi-circuit, multi-system sensor value table — so you can quickly determine good vs. bad readings across every major diesel system.
Fuel System
Rail pressure (PSI/bar), injector return flow (mL/min), lift pump pressure, filter restriction
Aftertreatment
DPF differential pressure (kPa), SCR inlet/outlet NOx (ppm), DEF quality (%), reductant pressure (PSI)
Air / Boost
Boost pressure (PSI/kPa), intake manifold temp (°F/°C), MAF (g/s), VGT position (%)
Electrical Supply
12V/24V supply voltage, 5V reference, ground voltage drop, CAN bus voltage (H/L)
Coolant / Thermal
Coolant temp (°F/°C), oil temp, EGR temp, DPF bed temp, SCR catalyst temp
Sensors / Signals
Sensor supply (V), signal voltage range, frequency signals (Hz), PWM duty cycle (%)
Access the Extended Reference from the Ext. Ref button in the chat toolbar. It opens as a slide-over panel with tabbed system categories, searchable values, and color-coded good/marginal/bad ranges.
Use the Extended Reference when the AI asks for a sensor reading and you want to pre-check whether your value is in range before reporting it.
Technician Chat™ is AI Diesel Tech's instant-answer assistant for diesel technicians. Ask it anything — fault code meanings, wiring questions, test procedures, torque specs, sensor locations, fluid capacities, firing orders, or general troubleshooting guidance. It maintains context across the conversation and is available on all paid plans.
What Technician Chat™ can answer:
- Torque specs — injectors, head bolts, turbo mounting, and more
- Sensor locations — where is the MAP sensor on a DD15?
- Fluid capacities — coolant, DEF, oil, transmission fluid
- Firing orders — any engine platform
- DEF system details — dosing rates, NOx thresholds, regen logic
- Common failure patterns — what usually causes SPN 3364?
- Quick code lookups — what does FMI 5 mean on a fuel injector circuit?
How to use Technician Chat™:
- Navigate to Technician Chat™ from the header or dashboard.
- Type your question in plain language — no special syntax needed.
- Technician Chat™ maintains context across the conversation, so you can ask follow-up questions naturally.
- Use the quick-prompt chips at the top for common question types.
- Access Technician Chat™ from inside a diagnostic session via the Reference Panel — no need to leave your active diagnosis.
- Technician Chat™ now supports DieselVision™ photo input for instant recognition of sensors, connectors, VIN plates, dash fault screens, and wiring diagrams.
Powered by ASE-Certified Logic
Technician Chat™ is trained on heavy-duty diesel systems — Cummins, Detroit, PACCAR, Volvo, and Navistar — and validated by an ASE Certified Diesel Technician. It is a reference tool; always verify specs against OEM documentation before performing work.
DieselVision™ is fully integrated into Technician Chat™, allowing multimodal photo-based mechanical assistance. It is AI Diesel Tech's advanced photo-accuracy system that enhances technician-uploaded photos using multi-pass vision analysis, glare reduction, OCR enhancement, and confidence scoring. DieselVision™ reads scanner screens, wiring diagrams, connectors, sensors, part numbers, and VIN plates with unmatched clarity — giving technicians cleaner, safer, more accurate diagnostics.
How to use DieselVision™:
- Tap the camera or gallery button in the Technician Chat™ input bar.
- Select what you're photographing from the type selector (scanner screen, wiring diagram, connector, etc.).
- Follow the pre-capture tips shown for your photo type to maximize accuracy.
- Take or upload the photo — DieselVision™ runs automatically.
- Review the extracted data (fault codes, VIN, pin assignments) with confidence badges.
- Confirm or correct any medium-confidence values, then tap Send to Diagnosis.
What DieselVision™ can read:
- Scanner screens — SPN/FMI codes, P-codes, live data PIDs
- Wiring diagrams — component nodes, wire colors, circuit paths
- Connector close-ups — connector ID and pin-by-pin assignments
- VIN plates and part number labels
- Dashboard clusters — warning lights and gauge readings
- Oscilloscope and multimeter screens
Confidence scoring
Every extracted value is scored high, medium, or low confidence. Medium-confidence values show an editable field so you can verify before sending. Low-confidence values are flagged — a retake prompt appears if photo quality is too poor to read accurately.
Ready to Diagnose?
You have everything you need. Start a session and let the Phase 2 FSM v7.0 guide you to the root cause.