OBD-II Fault Codes Explained: Complete Guide to P0300, P0171, P0420 & More (2025)
Your check engine light just came on. Here's exactly what P0300, P0171, P0420, and other fault codes mean—plus how much it costs to fix each one.
Featured Article
Expert insights on vehicle diagnostics, AI technology, and automotive care
Our content is organized into topic clusters to help you find comprehensive guides on specific subjects. Each cluster contains a pillar page and related posts.
Fault codes, diagnostic guides, and troubleshooting
Seasonal care, health monitoring, preventive maintenance
Used car buying, inspection, fraud detection
AI-powered failure prediction and smart diagnostics
Your check engine light just came on. Here's exactly what P0300, P0171, P0420, and other fault codes mean—plus how much it costs to fix each one.
Featured Article
Discover how SKANYX AI analyzes vehicle data to predict failures weeks before they happen. Learn about machine learning, pattern recognition, and predictive maintenance.
Real customer story: How SKANYX AI-powered diagnostics detected a hidden transmission problem before purchase, saving €2,500 and preventing a costly mistake.
Learn the 10 warning signs of transmission problems. Early detection saves thousands. Complete guide with diagnosis and repair costs.
A light just appeared on your dashboard. Is it urgent? Can you keep driving? This complete guide explains every warning light—when to pull over and when to schedule service.
Low oil pressure warning? STOP driving immediately. Learn what to do, causes, and how to prevent engine damage.
Traction control light on? Learn causes, diagnosis, and repair costs. Safety tips for driving with TC light.
Your ABS light is on. Learn what causes it, how to diagnose it, and repair costs. Safety tips and when you can still drive safely.
Airbag light on? Learn what it means, safety risks, and when you can still drive. Complete guide with repair costs.
Complete summer car care guide. Prevent overheating, maintain AC, and protect your car from heat damage.
Complete winter car maintenance checklist. 15 essential steps to prepare your car for cold weather and prevent breakdowns.
Complete fall car preparation guide. Get ready for winter with battery test, heating system check, and winter prep.
Honda and Acura error codes explained. Learn about VTEC system codes, transmission issues, SRS codes, and common Honda problems.
Complete spring car maintenance guide. Post-winter inspection, rust checks, fluid changes, and essential repairs.
Battery light on while driving? Learn what it means, how long you can drive, and alternator repair costs.
BMW-specific fault codes explained. Learn about VANOS codes, common BMW problems, and diagnostic guide for BMW vehicles.
Learn what information is in a vehicle history report, how to read it, and how to spot red flags. Complete guide to CARFAX, AutoCheck, and alternatives.
AI-powered diagnostics read 40+ vehicle modules faster than traditional scanners. Discover how machine learning predicts failures weeks before they happen—saving thousands in repairs.
Over $1 billion annually is wasted on unnecessary repairs due to misunderstood fault codes. Here are the 7 most damaging myths—and what they really cost you.
Tesla error codes and warning messages explained. Learn how to read Tesla diagnostics, use service mode, and understand Tesla-specific issues.
EV diagnostic tools guide. Learn how to diagnose electric vehicle problems, battery health monitoring, and specialized EV scanners.
Hybrid car warning lights explained. Learn about hybrid-specific warnings, battery system lights, and what's different from gas cars.
DIY vs mechanic guide. Learn which repairs are safe to DIY, which are dangerous, and when to hire a professional. Safety first.
Learn 10 easy DIY car repairs you can do at home. Save $1,000+ per year with step-by-step guides, tools needed, and safety tips.
Complete 2025 car repair cost guide. Average costs for engine, transmission, brakes, AC, electrical repairs. Know fair prices before visiting mechanic.
Learn how to verify vehicle service records, spot fake records, and check maintenance history when buying a used car.
Rebuilt title vs salvage title explained. Learn the differences, risks, insurance issues, and whether you should buy one.
Odometer fraud costs buyers $1+ billion annually. Here's how to spot mileage rollback, verify vehicle history, and avoid buying a rolled-back car.
Don't buy a flood-damaged car. Learn 12 ways to detect water damage, check for flood history, and protect your investment.
ECU programming and module coding explained. Learn what it is, tools needed, legal considerations, and how to unlock hidden features.
Master live data stream analysis with your OBD2 scanner. Learn to read PIDs, fuel trims, and sensor data like a pro.
Complete guide to choosing and using an OBD-II scanner. Compare features, prices, and learn how to read codes like a pro.
Bidirectional scanner controls explained. Learn what bidirectional means, active tests you can perform, and when you need them.
Avoid these 7 critical mistakes when buying a used car. Each one costs $2,500-$8,000 on average. Learn how to protect yourself.
Never buy a used car blind again. This complete checklist reveals odometer fraud, hidden damage, and saves you thousands in unexpected repairs.
P0420 code means your catalytic converter isn't working efficiently. Learn what causes it, how to diagnose it, and repair costs from $400-$2,500.
P0171 gets 31,000 searches monthly. Your engine is running with too much air. Here's what causes it, how to fix it yourself, and what it costs at a shop.
P0300 gets 45,000 searches monthly. A flashing check engine light means STOP DRIVING. Here's what causes misfires, how to diagnose them, and when it's safe to drive.
Real customer story: How SKANYX live data monitoring caught a failing transmission during a test drive. See how real-time monitoring saved thousands.
How SKANYX's AI-powered coding will beat OBDeleven: AI guidance, safety checks, easier use, and smarter coding. See why AI coding is the future.
Learn what car coding is, how it works, legal considerations, and when SKANYX coding features are coming. Complete guide to vehicle coding and customization.
SKANYX coding roadmap for 2026: planned features, beta signup, release timeline, and what coding capabilities are coming. Complete guide to SKANYX coding features.
Practical guide: What to watch for in SKANYX live data during test drives. Red flags, normal vs abnormal readings, and how to use live data for PPI.
Real use case: I asked SKANYX AI Chat 'Why does my car idle rough?' See the complete conversation, AI diagnosis, and how it helped me fix the problem.
Complete guide to dashboard warning lights. Learn what every warning light means, when to stop driving, how to diagnose issues, and what to do. Your comprehensive warning light reference.
Complete guide to OBD-II fault codes. Learn what P0300, P0171, P0420, and other codes mean, how to diagnose them, repair costs, and when to drive safely. Your comprehensive fault code reference.
Real customer story: How SKANYX Health Monitor detected a health score drop from 85 to 62, identified the cause, and helped fix it before it became expensive.
Learn 10 actionable ways to improve your car's health score. From regular maintenance to prompt repairs, these tips will boost your SKANYX health rating from 0-100.
Complete guide to buying used cars safely. Learn how to inspect vehicles, detect fraud, avoid hidden problems, and use AI-powered tools like SKANYX for pre-purchase inspections. Save thousands with this comprehensive guide.
Complete guide to AI-powered car diagnostics. Learn how SKANYX AI predicts failures, analyzes health scores, provides chat assistance, and compares to human mechanics. Everything you need to know about automotive AI.
Find car diagnostic services near you: mechanics, mobile services, auto parts stores. Compare costs (€150 mechanic vs €39 SKANYX) and learn when to DIY vs professional.
Learn the 15 most common car problems, their symptoms, how to diagnose each with SKANYX, DIY vs mechanic options, and cost estimates. Complete guide.
SKANYX feature updates: what's new, bug fixes, upcoming roadmap, and community feedback. Stay updated on latest SKANYX features and improvements.
Learn what car diagnostic is, how it works, types of diagnostics, and cost breakdown. Compare mechanic (€150) vs DIY with SKANYX (€39). Complete 2025 guide.
Honest Carly app review: pros, cons, pricing, and whether it's worth €60/year. Compare features, limitations, and alternatives like SKANYX for AI-powered diagnostics.
Direct comparison: SKANYX vs Carly for used car inspection. Compare features, accuracy, cost, and which AI-powered inspection is better for buying used cars.
Learn how SKANYX AI detects hidden problems in used cars that traditional inspections miss. Real examples, case studies, and how AI analysis saves thousands.
15-point AI-powered used car buying checklist using SKANYX. Step-by-step inspection guide with AI diagnostics, health scoring, and cost estimates to avoid lemons.
Real customer story: How SKANYX pre-purchase inspection helped negotiate €1,200 off a used BMW. See the complete negotiation process and ROI proof.
Quick guide: Inspect a used car with SKANYX AI in just 15 minutes. Step-by-step instructions, what to check, and how to avoid buying a lemon.
SKANYX AI Chat lets you ask car questions in plain English. Learn how it works, see example conversations, and discover how conversational AI makes diagnostics easy.
Learn what your car's health score means. SKANYX's 0-100 rating system explained: what each range means, how it's calculated, and what to do about low scores.
30 best gift ideas for car enthusiasts in 2025. From diagnostic tools to accessories, including SKANYX AI-powered diagnostics. Complete gift guide.
Learn how SKANYX AI predicts car failures 2 weeks before they happen. Real examples, accuracy data, and how predictive maintenance saves thousands in repairs.
Complete 3-way comparison: SKANYX vs OBDeleven vs Carly. Compare features, pricing, use cases, and which OBD2 app is best for your needs in 2025.
5 real case studies where SKANYX AI detected car failures that mechanics missed. See how AI's data analysis caught problems before they became expensive.
Controversial comparison: AI vs human mechanics. Data-driven analysis showing when AI wins, when humans win, and which catches more problems in real-world testing.
Compare how SKANYX AI Chat explains fault codes vs. mechanics. See side-by-side examples showing how AI makes diagnostics accessible with plain English explanations.
Use case guide: OBDeleven for coding, Carly for used cars, SKANYX for AI. When to use each app, which features matter, and how to choose the right one.
Your check engine light is on. Learn what it means, the 10 most common causes, when you can drive safely, how to diagnose it, and repair costs. Complete 2025 guide.
Toyota and Lexus diagnostic codes explained. Learn about VSC light, Prius hybrid system, common Toyota problems, and diagnostic guide.
Ford F-150 diagnostic codes explained. Learn about EcoBoost issues, transmission codes, 4WD system, and common F-150 problems.
Mercedes-Benz warning lights and fault codes explained. Learn about SBC brake system, Airmatic suspension, and common Mercedes problems.
Compare the best car diagnostic tools for 2025. OBD2 scanners, professional scan tools, mobile apps. Find the right tool for your needs and budget.
OBDeleven review: Is it worth €79.99? Honest pros, cons, and pricing analysis. OBDeleven is good for VW/Audi coding, but SKANYX is better for AI diagnostics.
Find the best OBD2 app for 2025. Compare top 7 apps: SKANYX (#1 for AI diagnostics), OBDeleven, Torque Pro, Carly, Carista. Features, pricing, which is best.
Comparing SKANYX and OBDeleven: features, pricing, diagnostic capabilities, and which AI-powered OBD2 app is better for your needs.
