Natural language input
Drivers can start with symptoms even before they have a scan result.
OBD-II diagnostic lookup
Enter your OBD-II code and get diagnosis help fast.
Search a fault code, get the meaning, see severity, review likely causes, and move into the right next checks before you replace parts blindly.
Code meaning Severity triage Likely causes First checks
CheckDTC / What a result page gives you
On every code page
Code → Cause
Meaning, urgency, common symptoms, likely causes, and first diagnostic checks.
Start with the code Open the exact DTC page in one search
Then decide what matters See severity + first checks before guessing
Need another entry point? Use symptom hubs, brand pages, and guides once you know what system the code points to.
New MVP
Symptom → likely cause → likely fix path
A new local-first AI diagnose flow lets users describe drivability issues in plain English, then review cautious ranked causes and a follow-up check plan.
Deterministic matching
The MVP uses local rules, keywords, and code mappings instead of hand-wavy AI claims.
Actionable next step
Each likely cause can open a practical first-check and fix-path plan.
Coverage
606
seed DTC pages with causes, severity, steps, and FAQ markup
Brands
14
OEM hubs to widen internal linking and search intent capture
Symptoms
51
problem-first paths for users who have no scan result yet
Guides
47
supporting troubleshooting content around high-intent repair topics
Why this product structure works
Built around the first questions drivers and technicians ask
Direct code intent
Dedicated code pages target exact searches like P0300, P0171, and P0420 with practical summaries.
Triage before parts
Each path emphasizes likely systems, severity, and next checks so the site feels diagnostic, not generic.
SEO without template rot
Routes stay static and scalable while the page framing feels like a real garage-tech tool.
Brand entry routes
Homepage brand paths now follow the same shared priority and family model as the brand layer
These homepage hubs are no longer a separate manual list. They follow the same reusable brand priority order that powers /brands, so core and expansion routes stay aligned as the graph deepens.
Toyota Japanese mainstream
Toyota OBD-II Trouble Codes
Start with common drivability and emissions faults first
113 codes · 9 symptom routes
Open brand hub Ford Detroit mainstream
Ford OBD-II Trouble Codes
Use as the domestic volume brand route for common powertrain and brake-switch faults
150 codes · 12 symptom routes
Open brand hub Honda Japanese mainstream
Honda OBD-II Trouble Codes
Best for lean, cooling, idle, and transmission complaints across mainstream Honda platforms
96 codes · 11 symptom routes
Open brand hub Chevrolet GM mainstream
Chevrolet OBD-II Trouble Codes
Primary GM volume route for ignition, EVAP, throttle, and transmission complaints
157 codes · 12 symptom routes
Open brand hub Jeep Mopar family
Jeep OBD-II Trouble Codes
Best Mopar SUV route for EVAP, TIPM, and oil-control complaints
10 codes · 5 symptom routes
Open brand hub Dodge Mopar family
Dodge OBD-II Trouble Codes
Good first stop for gas-cap EVAP complaints and throttle intervention faults
10 codes · 5 symptom routes
Open brand hubBrand families
Start with the right badge cluster when platform overlap matters more than one exact make
These family-level entry routes turn the homepage into a real bridge toward sibling brands instead of only exposing isolated hubs, including thinner GM premium/truck and German premium branches that were previously harder to discover.
Asian mainstream leaders 2 hubs
Toyota leads this route
High-volume Japanese brands where broad drivability and emissions search demand already justifies deep code-to-symptom routing.
Best first stop for broad owner search intent
Shared systems: fuel trim, cooling, brake switch / cruise logic
Core: Toyota, Honda · Expansion: —
Detroit mainstream coverage 2 hubs
Ford leads this route
Large domestic entry points that catch everyday Ford and Chevrolet fault lookups before users narrow into sibling makes.
Strong national search demand and broad shared systems
Shared systems: EVAP, electronic throttle control, cooling fans
Core: Ford, Chevrolet · Expansion: —
Mopar truck and SUV cluster 4 hubs
Jeep leads this route
Jeep, Dodge, Chrysler, and Ram share enough EVAP, oil-control, throttle, and communication patterns to deserve a tight sibling graph.
Cross-shop intent benefits from shared family routing
Shared systems: EVAP leak detection, oil pressure / oil-control circuits, TIPM / module communication
Core: — · Expansion: Jeep, Dodge, Ram
Thin direct-entry hubs kept discoverable here: Chrysler
Volkswagen Auto Group pathways 2 hubs
Volkswagen leads this route
Volkswagen and Audi hubs are strongest when they expose lean-idle, fuel-pressure, secondary-air, and gateway fault overlap together.
Good candidate for deeper premium + mainstream pairing
Shared systems: direct injection fuel pressure, secondary air injection, intake manifold runner control
Core: — · Expansion: Volkswagen
Thin direct-entry hubs kept discoverable here: Audi
GM truck and premium branches 3 hubs
GMC leads this route
GMC, Cadillac, and Buick now extend GM routing beyond Chevrolet so reduced-power and timing-correlation searches do not collapse into one badge.
High-value support hubs around existing GM code depth
Shared systems: electronic throttle control, accelerator pedal correlation, VVT correlation
Core: — · Expansion: GMC
Thin direct-entry hubs kept discoverable here: Cadillac, Buick
European premium anchor 1 hubs
BMW leads this route
BMW remains a premium-brand anchor and a useful bridge into Audi and Volkswagen diagnosis paths.
Premium support route with broad code adjacency
Shared systems: electronic throttle control, fuel-pressure regulation, cooling fan control
Core: — · Expansion: BMW
Featured trouble codes
High-intent pages users actually want to open
P0300 high
Random/Multiple Cylinder Misfire Detected
The ECU detected misfire activity across multiple cylinders rather than one isolated cylinder.
Open diagnostic page P0171 medium
System Too Lean (Bank 1)
The ECU is adding fuel because Bank 1 is running lean beyond normal correction limits.
Open diagnostic page P0420 medium
Catalyst System Efficiency Below Threshold (Bank 1)
Catalyst monitoring suggests Bank 1 converter performance is below expected threshold.
Open diagnostic page P0442 low
EVAP System Leak Detected (Small Leak)
The EVAP monitor found a small leak in the fuel vapor containment system.
Open diagnostic page P0455 low
EVAP System Leak Detected (Large Leak)
The EVAP monitor found a large leak or a system unable to hold pressure or vacuum.
Open diagnostic page P0301 high
Cylinder 1 Misfire Detected
The ECU detected misfire events concentrated in cylinder 1.
Open diagnostic pageBest starting points
Choose the right entry into the diagnostic flow
Know the code already?
Starting from behavior?
Connected paths
Popular codes to browse
Built to keep related fixes, symptoms, and hubs one step away.
P0300 — Random/Multiple Cylinder Misfire DetectedP0301 — Cylinder 1 Misfire DetectedP0302 — Cylinder 2 Misfire DetectedP0303 — Cylinder 3 Misfire DetectedP0304 — Cylinder 4 Misfire DetectedP0305 — Cylinder 5 Misfire DetectedP0306 — Cylinder 6 Misfire DetectedP0307 — Cylinder 7 Misfire DetectedP0308 — Cylinder 8 Misfire DetectedP0171 — System Too Lean (Bank 1)
Connected paths
High-priority drivability codes
Built to keep related fixes, symptoms, and hubs one step away.
Connected paths
Brand hubs
Built to keep related fixes, symptoms, and hubs one step away.
Toyota · Japanese mainstreamFord · Detroit mainstreamHonda · Japanese mainstreamBMW · German premiumChevrolet · GM mainstreamJeep · Mopar familyDodge · Mopar familyChrysler · Mopar familyRam · Mopar familyVolkswagen · VAG familyAudi · VAG familyGMC · GM mainstreamCadillac · GM mainstreamBuick · GM mainstream
Connected paths
Common symptoms
Built to keep related fixes, symptoms, and hubs one step away.
Engine MisfireRough IdlePoor Fuel EconomyHard StartFuel SmellFuel Smell Near Rear WheelCheck Engine Light After Gas CapCheck Engine Light FlashingReduced PowerLong CrankHard Start After RefuelingCar Hard to Start After Getting GasEngine Runs Rough After RefuelingCar Runs Rich After Getting GasRough Idle After RefuelingBlack Smoke After RefuelingCar Flooded After Getting GasNo Start But CranksPump Keeps Clicking OffDifficulty Filling Gas TankCar Smells Like Gas After RefuelingCar Stalls After Getting GasEVAP Code Keeps Coming BackFailed Emissions TestFailed Emissions Test: EVAP Not ReadyMisfire After RefuelingCatalyst Code After MisfireRotten Egg Smell After MisfireExhaust Smells Like SulfurP0420 But Car Runs FineCheck Engine Light Flashing After Getting GasTicking Noise and Check Engine LightP0171 After Exhaust WorkHarsh ShiftingStuck in Limp ModeWon’t UpshiftHigh Highway RPMTorque Converter Won’t LockPoor Highway MPGBattery Light OnEngine OverheatingA/C Gets Warm at IdleFuel Gauge IncorrectSecurity Light OnReduced Engine Power MessageBrake Light Switch ProblemsCruise Control Not WorkingHard Brake PedalReduced Brake AssistEngine Runs Too CoolTakes Too Long to Warm Up
Connected paths
Guides
Built to keep related fixes, symptoms, and hubs one step away.
How to Diagnose an Engine Misfire Step by StepHow to Read Live Fuel Trim Data Without GuessingHow to Test an EVAP Purge Valve Without GuessingEVAP Small Leak Checklist Before Replacing PartsGas Cap vs EVAP Leak: How to Tell What Is Actually WrongFuel Tank Pressure Sensor vs EVAP Leak: How to Tell the DifferenceCan You Drive With a Flashing Check Engine Light?Vacuum Leak Checklist for Lean Codes and Rough IdleHard Start Diagnostic Order for OBD-II VehiclesReduced Power Initial ChecklistLong Crank Diagnostic Order Before Replacing SensorsNo Start But Cranks Checklist for OBD-II VehiclesRefuel-Related Hard Start Checklist: Purge, Vent, and Pressure CluesPurge Valve Stuck Open vs Flooded Charcoal Canister: How to Tell Which One Is Causing the Refuel ProblemWhy Topping Off the Gas Tank Damages the EVAP SystemBad Gas vs EVAP Purge Problem: How to Tell Which One You Actually HaveEVAP Vent Valve vs Purge Valve: How to Tell Which Side of EVAP Is FailingP0420 vs Bad O2 Sensor vs Exhaust Leak: How to Tell Which One Is Actually Setting the StoryRear O2 Sensor Code vs Bad Catalytic Converter: How to Tell Which One Is Actually WrongP0300 Then P0420: What It Usually MeansRefuel Misfire vs Ignition Misfire: How to Tell Which One You Actually HaveExhaust Leak vs Bad O2 Sensor vs True Lean Condition: How to Tell Which Story the Engine Is Actually TellingP0016 vs P0335 vs P0340: How to Tell Timing Correlation from Crank or Cam Signal FailureStartup Rattle with P0016 or P0017: What It Usually MeansP0011 vs P0016 vs P0340: VVT Solenoid, Sensor, or Timing Chain?Long Crank Hot vs Cold: What Cam, Crank, and EVAP Codes Are Trying to Tell YouPost-Catalyst Fuel Trim Codes vs Rear O2 Sensor vs Catalytic Converter: How to Tell Which One Is Actually WrongTorque Converter Won’t Lock: High Highway RPM vs Real SlipP0700 vs P0715 vs P0730: How to Split Bad Transmission Data from Real SlipBattery Light On: Bad Battery, Alternator, or Wiring?P219A / P219B vs P0300 vs P0171 / P0174: Bank Imbalance or General Lean-Misfire Problem?Fuel Rail Pressure Sensor vs Regulator Control: How to Tell Which Side of the Fuel System Is Actually FailingEVAP Leak Detection Pump vs Vent Valve vs Switching Valve: How to Tell Which EVAP Hardware Is Actually FailingFailed Emissions Test: Active Code vs Monitor Not ReadyPCM Power Relay vs Battery vs Ignition Switch: How to Split a No-Start Power ProblemFuel Level Sender vs Wiring vs Instrument Cluster: How to Tell What Is Actually WrongSecurity Light On: Wrong Key vs Immobilizer Module vs Power ProblemEngine Overheats in Traffic vs on the Highway: What That Usually MeansReduced Engine Power: Throttle Body vs Pedal vs Low VoltageBrake Switch vs Brake Light Circuit: How to Tell What Is Actually WrongCruise Control Won't Engage: Brake Switch vs Clutch Switch vs Speed SignalHard Brake Pedal: Brake Booster vs Vacuum Leak vs Pressure SensorEngine Runs Too Cool: Thermostat vs Sensor vs WiringSlow Warmup: Thermostat vs Coolant Sensor vs False-Cold DataP0125 vs P0128 vs P0118: Open Loop Too Long vs Thermostat vs False-Cold ECTP2761 vs P0743 vs P0741: Open Circuit vs Electrical Fault vs TCC PerformanceHigh Highway RPM in Top Gear: No Lockup vs No Overdrive