OBD-II Code Database
Search our database of common diagnostic trouble codes. Get the full diagnosis and repair guide in the CarFixAI app.
Showing 25 of 25 codes
Random/Multiple Cylinder Misfire Detected
The engine control module has detected misfires occurring in multiple cylinders or at random. This can cause rough running, reduced power, and increased emissions.
System Too Lean (Bank 1)
The engine is running with too much air and not enough fuel. Common causes include vacuum leaks, faulty MAF sensor, or fuel delivery issues.
Catalyst System Efficiency Below Threshold
The catalytic converter is not operating efficiently enough to meet emissions standards. May be caused by a failing converter, oxygen sensor issues, or engine problems.
Coolant Thermostat Below Regulating Temperature
The engine is taking too long to reach operating temperature. Usually indicates a thermostat stuck open or a faulty coolant temperature sensor.
Evaporative Emission System Malfunction
General code indicating a problem with the EVAP system that captures fuel vapors. Could be as simple as a loose gas cap.
Evaporative Emission System Leak Detected (Small)
A small leak has been detected in the EVAP system. Often caused by a loose or damaged gas cap, or a small crack in a hose or canister.
Evaporative Emission System Leak Detected (Large)
A large leak has been detected in the EVAP system. Check for a missing gas cap first, then inspect hoses and the charcoal canister.
Cylinder 1 Misfire Detected
The engine control module has detected misfires specifically in cylinder 1. Check spark plugs, ignition coils, fuel injectors, and compression.
Cylinder 2 Misfire Detected
The engine control module has detected misfires specifically in cylinder 2. Check spark plugs, ignition coils, fuel injectors, and compression.
Cylinder 3 Misfire Detected
The engine control module has detected misfires specifically in cylinder 3. Check spark plugs, ignition coils, fuel injectors, and compression.
Cylinder 4 Misfire Detected
The engine control module has detected misfires specifically in cylinder 4. Check spark plugs, ignition coils, fuel injectors, and compression.
System Too Rich (Bank 1)
The engine is running with too much fuel and not enough air. Can be caused by faulty oxygen sensors, fuel pressure issues, or a dirty MAF sensor.
Exhaust Gas Recirculation Flow Insufficient
The EGR system is not flowing enough exhaust gas back into the intake. Often caused by carbon buildup in EGR passages or a faulty EGR valve.
Catalyst System Efficiency Below Threshold (Bank 2)
Similar to P0420, but for bank 2 (usually the right side on V engines). The catalytic converter on this side is not operating efficiently.
Vehicle Speed Sensor Malfunction
The vehicle speed sensor is not providing a signal or the signal is erratic. This affects speedometer operation and may cause transmission shifting issues.
Transmission Control System Malfunction
General code indicating the transmission control module has detected a fault. Additional codes will usually be stored with more specific information.
Input/Turbine Speed Sensor Circuit Malfunction
The transmission input speed sensor is not functioning properly. This affects shift timing and can cause harsh shifts or failure to shift.
Incorrect Gear Ratio
The transmission is not achieving the expected gear ratio. Could indicate internal transmission problems, low fluid, or solenoid issues.
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
The heated oxygen sensor heater circuit is not functioning. This causes delayed warm-up and increased emissions during cold starts.
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
The downstream oxygen sensor heater circuit is not functioning. This affects the ability to monitor catalytic converter efficiency.
Camshaft Position Sensor Circuit Malfunction
The camshaft position sensor signal is missing or erratic. This can cause starting problems, rough running, or no start conditions.
Crankshaft Position Sensor Circuit Malfunction
The crankshaft position sensor signal is missing or erratic. Often causes no start, stalling, or intermittent running issues.
Intake Air Temperature Sensor Circuit High Input
The intake air temperature sensor is reading too high. This affects fuel mixture calculations and may cause performance issues.
Mass Air Flow Sensor Circuit Range/Performance
The MAF sensor reading is outside expected range. Often caused by a dirty sensor, air leaks, or actual sensor failure.
Manifold Absolute Pressure Sensor Range/Performance
The MAP sensor reading is outside expected range. Check for vacuum leaks, sensor issues, or wiring problems.
What is an OBD-II Code?
OBD-II (On-Board Diagnostics, version 2) is a standardized system that monitors your vehicle's emissions and engine performance. When the computer detects a problem, it stores a Diagnostic Trouble Code (DTC) and illuminates the check engine light.
Code Format Explained
- P - Powertrain (engine/transmission)
- B - Body
- C - Chassis
- U - Network
- 0 - Generic (SAE standard)
- 1 - Manufacturer specific
Indicates the specific system (fuel, ignition, emissions, etc.)
Specific fault identified within the system
How to Read Your OBD-II Code
You can read OBD-II codes using a scan tool that plugs into the OBD-II port, typically located under the dashboard near the steering column. Many auto parts stores will read codes for free, or you can purchase an inexpensive Bluetooth OBD-II adapter.
Once you have your code, enter it into CarFixAI for a complete diagnosis including probable causes, repair difficulty, cost estimates, and step-by-step repair guides.
Get the Full Diagnosis
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