Diagnose & Fix Check Engine Light Codes Without Dealer Repair Bills
Stop guessing with expensive replacement parts. Look up your diagnostic trouble code to get verified 80/20 root causes, multimeter sensor specs, and step-by-step DIY repair guides.
Read the Fault Code
Plug in a $25 Bluetooth OBD2 scanner to retrieve the exact DTC code.
Verify the 80/20 Fix
Test sensor voltages and check vacuum hoses before buying costly components.
Fix & Clear CEL
Follow our garage checklist to replace the part and extinguish the light.
Mechanic Shop Bill vs DIY Driveway Cost Calculator
Select your trouble code to compare average dealer shop quotes against verified DIY fix costs.
Browse Trouble Codes by Vehicle System
Powertrain
Engine, fuel delivery, unmetered air leaks, ignition coils, misfires & emissions.
Chassis & Brakes
ABS wheel speed sensors, traction control (ESP/VSC), steering angle & suspension.
Body Systems
Airbags (SRS safety), climate control HVAC, power windows, locks & lighting.
CAN Bus & Network
Inter-module communication loss, high/low CAN bus lines & gateway errors.
Most Common Engine Trouble Codes
The top trouble codes triggering Check Engine Lights across North America and Europe.
| DTC Code | Official Name & System | Severity Level | DIY Cost vs Mechanic | Repair Manual |
|---|---|---|---|---|
| P0171 | System Too Lean (Bank 1) Fuel & Air Metering | Moderate (Fix Soon) | $15 – $45 / $220 – $480 | View Guide |
| P0300 | Random / Multiple Cylinder Misfire Detected Ignition & Combustion | Severe (Stop & Fix) | $35 – $120 / $280 – $750 | View Guide |
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) Emissions & Exhaust | Moderate (Fix Soon) | $25 – $180 / $850 – $2,200 | View Guide |
| P0455 | Evaporative Emission Control System Leak Detected (Gross / Large Leak) EVAP & Emissions | Low (Safe to Drive) | $12 – $45 / $150 – $350 | View Guide |
| P0442 | Evaporative Emission Control System Leak Detected (Small Leak) EVAP & Emissions | Low (Safe to Drive) | $12 – $65 / $150 – $380 | View Guide |
| P0128 | Coolant Thermostat (Coolant Temp Below Regulating Temperature) Cooling System | Low (Safe to Drive) | $18 – $45 / $180 – $380 | View Guide |
| P0174 | System Too Lean (Bank 2) Fuel & Air Metering | Moderate (Fix Soon) | $15 – $45 / $220 – $480 | View Guide |
| P0430 | Catalyst System Efficiency Below Threshold (Bank 2) Emissions & Exhaust | Moderate (Fix Soon) | $25 – $180 / $850 – $2,200 | View Guide |
| P0011 | Camshaft Position 'A' - Timing Over-Advanced (Bank 1) Variable Valve Timing (VVT) | Moderate (Fix Soon) | $25 – $85 / $220 – $580 | View Guide |
| P0014 | 'B' Camshaft Position Timing Over-Advanced (Bank 1) Engine Mechanical & VVT | Moderate (Fix Soon) | $25 – $65 / $210 – $420 | View Guide |
| P0101 | Mass or Volume Air Flow Circuit Range/Performance Fuel and Air Metering | Moderate (Fix Soon) | $15 – $65 / $160 – $350 | View Guide |
| P0113 | Intake Air Temperature (IAT) Sensor 1 Circuit High Input Fuel & Air Metering | Low (Safe to Drive) | $15 – $45 / $120 – $240 | View Guide |
System Too Lean (Bank 1)
Fuel & Air Metering
Random / Multiple Cylinder Misfire Detected
Ignition & Combustion
Catalyst System Efficiency Below Threshold (Bank 1)
Emissions & Exhaust
Evaporative Emission Control System Leak Detected (Gross / Large Leak)
EVAP & Emissions
Evaporative Emission Control System Leak Detected (Small Leak)
EVAP & Emissions
Coolant Thermostat (Coolant Temp Below Regulating Temperature)
Cooling System
System Too Lean (Bank 2)
Fuel & Air Metering
Catalyst System Efficiency Below Threshold (Bank 2)
Emissions & Exhaust
Camshaft Position 'A' - Timing Over-Advanced (Bank 1)
Variable Valve Timing (VVT)
'B' Camshaft Position Timing Over-Advanced (Bank 1)
Engine Mechanical & VVT
Mass or Volume Air Flow Circuit Range/Performance
Fuel and Air Metering
Intake Air Temperature (IAT) Sensor 1 Circuit High Input
Fuel & Air Metering
Browse Common Trouble Codes by Manufacturer
Select your vehicle make to see common Technical Service Bulletins (TSBs) and frequent failure points.
The Essential DIY Diagnostic Tool Kit
Stop blindly throwing replacement parts at your engine. These 6 specialized tools cost less than a single hour of dealer shop diagnostic labor ($180/hr) and let you fix 90% of OBD-II fault codes yourself.
Bluetooth Wireless OBD2 Scanner (Live Data)
Reads live engine sensors (fuel trims, coolant temp, O2 voltages) and resets check engine lights directly from your smartphone.
Automotive Smoke Machine Leak Detector
Fills the intake or EVAP system with safe dense smoke to pinpoint invisible vacuum hose tears and pinhole leaks in 30 seconds.
Automotive Digital Multimeter with Back-Probes
Crucial for testing 5V reference wires, sensor ground continuity, and injector pulses without puncturing factory silicone wire seals.
Magnetic Swivel Spark Plug Socket Set
Strong interior magnet grips spark plugs safely inside tight cylinder heads without dropping or cracking ceramic insulators.
CRC Mass Air Flow & Throttle Body Cleaner Duo
Dissolves carbon deposits and sensor hot-wire film without leaving conductive residue or stripping protective throttle coatings.
Infrared Non-Contact Pyrometer Gun
Instantly validates catalytic converter efficiency (inlet vs outlet temp), thermostat opening temperature, and sticking brake calipers.