Stop Guessing
and Start Testing.
Enter any fault code — SPN/FMI, OBD-II, or OEM dash code — and receive the exact test sequence to run next. Structured, step-by-step process of elimination engineered by an ASE Certified Diesel Technician.
Diagnostic Search
Works on all SPN/FMI and OBD-II codes. Plans from $12.95/mo.
Got fault code P0087 on my T680. Truck is losing power under load.
AI Diesel Tech
P0087 — Fuel Rail Pressure Too Low. The high-pressure fuel rail maintains 23,000–26,000 PSI for injection.
Step 1: Connect your scan tool and monitor live fuel rail pressure (PID: FRP) at idle. Note the reading.
Is the fuel rail pressure reading below 20,000 PSI at idle?
ASE Certified
Diesel Tech — not a startup guess
1,830+ Fault Codes
SPN/FMI & OBD-II — free to search
40+ Platforms
Class 8 to diesel pickups
From $12.95/mo
Cancel anytime
Get DVOM Certified.
Test like a pro.
A complete 8-module DVOM and multimeter training course built for diesel technicians. Real SPN/FMI scenarios, interactive quizzes, and a printable certificate issued by AI Diesel Tech.
DieselVision™ Photo Diagnostics
Inside Technician Chat™
Snap a photo of anything on the truck. DieselVision™ reads it instantly — no typing required. The fastest way to get mechanical info from the shop floor.
Snap a photo of
VIN plates
Auto-fills vehicle info
Dash fault screens
Extracts SPN/FMI codes
Warning lights
Identifies active faults
Sensors & connectors
Names components
DPF/SCR labels
Reads part numbers
Any diesel component
Instant identification
What DieselVision™ does
What's this fault on my dash?
DieselVision™ Analysis
SPN 3364 — NOx Sensor Downstream. FMI 5 = open circuit or voltage below normal.
Step 1: Inspect the NOx sensor harness connector at the tailpipe outlet for corrosion or spread pins.
No typing required
Snap → instant answer
1,830 Codes — Free, No Login, No Paywall
The Fault Code Reference Built for the Shop Floor
Every SPN/FMI and OBD-II code includes symptoms, root causes, derate risk, and inducement flags — the same depth any experienced diesel tech needs on a hard fault. Bookmark it. Use it daily. It's free.
1,830 codes — no account required
Three steps to a clean repair
The same systematic process an experienced diesel tech uses on the floor — one physical test at a time, every step confirmed before moving on.
Takes 10 seconds
Enter Code or VIN
Type any DTC, SPN/FMI, or scan your VIN. Upload a photo of your scanner screen — the AI reads it directly.
One step at a time
Follow the Tests
The diagnostic engine walks you through a strict process of elimination — one physical test at a time. No shortcuts, no guesswork.
Professional PDF export
Get Repair Summary
Generate a professional repair summary with all steps, findings, and verification — ready for your records or the customer.
Enter your SPN/FMI or OBD-II code and get a step-by-step repair path.
Works on all SPN/FMI codes.
AI-Powered Diagnostics
SPN/FMI, OBD-II, photo upload
DVOM Training Academy
8 modules · certification
Repair Summaries
Professional PDF export
Why Techs Choose AI Diesel Tech
Designed for hands-on technicians, with training that reinforces real diagnostic logic.
Every diagnosis follows the same systematic process an experienced diesel tech uses — one physical test at a time, no skipping steps, no throwing parts at the wall.
ASE-Certified Diagnostic Logic
Step-by-step process of elimination — the same approach a seasoned diesel tech uses. No fluff, no guesswork.
Heavy-Duty & Diesel Pickup Coverage
Works on Class 8 semis, medium duty, and diesel pickups. Cummins, Detroit, PACCAR, Powerstroke, Duramax, RAM Cummins and more.
Image Upload for DTCs
Snap a photo of your scanner screen or wiring diagram. The AI reads it and incorporates it directly into the diagnostic flow.
PDF Repair Summaries
Every completed diagnosis generates a professional repair summary — all steps, findings, and verification in one clean document.
Mobile + PWA Friendly
Use it on your phone under the hood, on a tablet in the cab, or at your desk. Installs as a PWA — no app store required.
Coverage
40+ Engine Platforms
Heavy Duty — J1939
Caterpillar
Diesel Pickups — OBD-II
Medium Duty & Equipment
Detroit
DD15 · 14.8L
Cummins
ISX15 · 15.0L
PACCAR
MX-13 · 12.9L
Instant VIN Scanning for Diesel Trucks
DieselVision™ VIN Photo lets technicians capture a VIN label with a single tap and instantly auto-fill vehicle information using AI-powered OCR. No typing, no mistakes, and no wasted time. Upload a VIN photo and DieselVision™ extracts all 17 characters with high-confidence scoring, glare reduction, and plate-orientation correction.
- AI-powered VIN extraction from photos
- Automatic glare reduction and sharpening
- Orientation correction for angled VIN plates
- High-confidence scoring with green/amber indicators
- Instant auto-fill of vehicle year, make, model, and engine platform
- Works on cab VIN plates, door jamb labels, and frame-mounted tags
- Fully integrated into AI Diagnosis and Technician Chat™
VIN
1XPBD49X4JD123456
Year
2018
Make
Peterbilt
Engine
PACCAR MX-13
VIN auto-filled — ready to diagnose
Introducing DieselVision™ — Next-Gen Photo Accuracy
AI Diesel Tech's advanced photo-accuracy system. It enhances technician-uploaded photos using multi-pass vision analysis, glare reduction, OCR enhancement, and confidence scoring — giving technicians cleaner, safer, more accurate diagnostics.
Scanner screen OCR
Reads SPN/FMI, P-codes, and live data from any scan tool screen.
Wiring diagram parsing
Extracts component nodes, wire colors, and circuit paths from diagrams.
Connector pin mapping
Identifies connector IDs and pin assignments from close-up photos.
Confidence scoring
Every extracted value is scored high / medium / low — you confirm before it goes to diagnosis.
No credit card required for free diagnostic sessions.
From the Shop Floor
Techs who use it, trust it
"Diagnosed a P0087 on a Peterbilt 579 in under 20 minutes. The AI walked me straight to a cracked fuel line I would've missed. Saved me 3 hours of guessing."
Marcus T.
Lead Diesel Tech — Midwest Fleet Services
"I've been wrenching for 18 years and this thing thinks like a senior tech. The step-by-step process is exactly how I was trained — no shortcuts, no guessing."
Ray D.
Independent Mechanic — Dallas, TX
"I hand the PDF to the customer — they see every test we ran, every result. No more 'how do I know you actually checked that?' conversations. Builds trust instantly."
Sandra K.
Shop Owner — K&L Heavy Equipment
Included with every plan
Professional Repair Summaries — in seconds.
Enter your vehicle info, technician notes, and root cause. The AI formats it into a clean, dealership-grade repair summary you can print or hand to the customer — no more writing ROs from scratch.
- Auto-decodes VIN — year, make, model, engine, drive type
- Converts raw tech notes into professional documentation
- Includes diagnostic codes with plain-English meanings
- Print-ready PDF output — hand it straight to the customer
- Included on all plans — Micro, Quick Access, and Standard
Enter your SPN/FMI or OBD-II code and get a step-by-step repair path.
Works on all SPN/FMI codes.
Already have an account? Sign in to use it now.
Diagnostic Codes
- ›SPN 3251 FMI 0 — SCR Catalyst Efficiency Above Normal
- ›SPN 4094 FMI 18 — Reductant Quality Below Normal
Root Cause (Technician-Reported)
- ›Contaminated DEF fluid causing SCR catalyst degradation and reductant quality fault.
Work Performed
- ›Technician connected Cummins Insite and retrieved active fault codes.
- ›DEF quality tested — contamination confirmed at 28% urea (spec: 32.5%).
- ›DEF tank drained and flushed. Fresh DEF filled to capacity.
- ›SCR system purged and catalyst regeneration cycle initiated.
- ›Faults cleared. Road test completed — no return codes. Derate resolved.
Included with every plan
Instant answers. No diagnosis needed.
Need a torque spec mid-job? Can't remember the firing order? Just ask. Technician Chat™ gives you fast, accurate mechanical reference data without launching a full diagnostic session.
- Torque specs for any engine platform — DD, PACCAR, Cummins, Volvo
- Sensor and component locations on any commercial truck
- Fluid capacities — oil, coolant, DEF, transmission, axle
- SPN/FMI and fault code meanings explained in plain English
- Included on all plans — Micro, Quick Access, and Standard
Enter your SPN/FMI or OBD-II code and get a step-by-step repair path.
Works on all SPN/FMI codes.
Already have an account? Sign in to use it now.
Real results from real techs
"Fixed my DEF issue in 20 minutes. Saved me a $600 shop bill."
Marcus T.
Owner-Operator — Kenworth T680
"Found the real cause behind SPN 4364 FMI 18. No guessing."
Derek W.
Fleet Tech — Cummins ISX15
"Saved me $600 in shop labor. Diagnosed a boost leak in two steps."
Ray S.
Independent Tech — Detroit DD15
Pricing
Simple, honest pricing
Plans start at $12.95/mo. Cancel anytime.
On-Demand
BEST STARTTry it out — 3 full diagnoses/mo
3 diagnoses/month · cancel anytime
- 3 AI diagnostic sessions/mo
- Technician Chat™ included
- Full diagnostic engine
- PDF repair summaries
- Image & screenshot upload
- VIN decode included
- Mobile & PWA access
Cancel anytime.
Quick Access
POPULARSolo techs — full engine, no commitment
10 diagnoses/month · cancel anytime
- 10 AI diagnostic sessions/mo
- Technician Chat™ included
- Full diagnostic engine — every fault code
- PDF repair summaries
- Image & screenshot upload
- VIN decode included
- Mobile & PWA access
- Under $2 per diagnosis
Cancel anytime.
Standard
STANDARDFor shops ready to work smarter
or $950/year — save 20%
- 4 users included
- 60 diagnoses/mo
- Under $2 per diagnosis
- Technician Chat™ included
- Image & screenshot upload
- PDF repair summaries
- Mobile & PWA access
Cancel anytime.
Pro
SOONFor high-volume shops and fleets
or $1,990/year — save 20%
- Everything in Standard
- 8 users included
- Technician Chat™ included
- Priority AI response
- Fleet reporting
- API access
- Dedicated support
What Technicians Are Saying
Real feedback from diesel technicians using AI Diesel Tech in the field.
"I had a Cummins X15 with an intermittent SPN 157 that had stumped us for two days. AI Diesel Tech walked me through a fuel restriction test sequence I hadn't considered and we had the root cause in under 20 minutes. Primary filter was the culprit — saved us from replacing the high-pressure pump."
"The Repair Summary Builder alone is worth signing up. I used to spend 30 minutes writing up repair orders after every job. Now I type my notes and it generates a professional summary I can email directly to the customer. My shop looks more professional and I save hours every week."
"What I appreciate most is that it doesn't just throw parts at the problem. Every step has a reason. When it tells me to check a voltage, it tells me what I'm looking for and what the result means. That's how a master tech thinks — and that's what this platform delivers."
"We had a DEF quality fault that two other shops couldn't resolve. They replaced the NOx sensor twice. AI Diesel Tech identified it as a DEF concentration issue in the first test sequence. Drained the tank, refilled with verified DEF, and the truck was back in service the same day."
"I use Technician Chat™ every day for quick questions — torque specs, wiring questions, test procedures. It's like having a master tech on call 24/7. The context it keeps across the conversation is impressive. It remembers what we were working on."
"Diagnosed my Duramax fuel pressure issue faster than my scan tool. This thing is legit."
"We use it for quick triage. Cuts diagnostic time in half and customers love the PDF report."
"I've been wrenching 22 years. This AI thinks like a seasoned tech — no guessing, no shortcuts."
Everything a Diesel Tech Needs
Guides, fault code references, and diagnostic tools — all free to browse.
Technician Articles
- How to Diagnose DEF Derate — SPN 5246
- Top 10 PACCAR MX Fault Codes
- How J1939 SPN/FMI Codes Work
- Why Shops Misdiagnose Aftertreatment
Fault Code Library
- SPN 5246 FMI 31 — SCR Inducement
- SPN 4364 FMI 18 — SCR Efficiency
- SPN 157 FMI 3 — Fuel Rail Pressure
- SPN 3031 — DPF Soot Load
Compare Tools
ASE Practice Tests
Free 25-question practice exams for T2, T4, T6, T8, and L2 diesel certifications. Auto-graded with full explanations.
All practice testsGet started today
Your next hard fault ends
with a confirmed fix.
Type a fault code. Get the exact test to run. Work through it step by step until it's done.
Plans start at $12.95/mo. Cancel anytime.
Enter your SPN/FMI or OBD-II code and get a step-by-step repair path.