OBD-II Fault Codes

Pick your code for a mechanic-grade explanation — causes ranked by probability, whether you can keep driving, and repair costs.

Emissions System

P0420 — Catalyst System Efficiency Below Threshold (Bank 1)P0430 — Catalyst System Efficiency Below Threshold (Bank 2)P0135 — O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)P0141 — O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)P0130 — O2 Sensor Circuit Malfunction (Bank 1, Sensor 1)P2195 — O2 Sensor Signal Stuck Lean (Bank 1, Sensor 1)P0131 — O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)P0137 — O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)P0133 — O2 Sensor Slow Response (Bank 1, Sensor 1)

Fuel & Air System

P0171 — System Too Lean (Bank 1)P0174 — System Too Lean (Bank 2)P0101 — Mass Air Flow Sensor Range/PerformanceP2187 — System Too Lean at Idle (Bank 1)P2189 — System Too Lean at Idle (Bank 2)P2293 — Fuel Pressure Regulator 2 PerformanceP0113 — Intake Air Temperature Sensor 1 Circuit High (Bank 1)P0506 — Idle Air Control System RPM Lower Than ExpectedP0507 — Idle Air Control System RPM Higher Than Expected

Ignition System

P0300 — Random/Multiple Cylinder Misfire DetectedP0301 — Cylinder 1 Misfire DetectedP0340 — Camshaft Position Sensor Circuit MalfunctionP0335 — Crankshaft Position Sensor Circuit MalfunctionP0011 — "A" Camshaft Position — Timing Over-Advanced (Bank 1)P0014 — "B" Camshaft Position — Timing Over-Advanced (Bank 1)P0325 — Knock Sensor Circuit Malfunction (Bank 1)P0021 — "A" Camshaft Position — Timing Over-Advanced (Bank 2)P0012 — "A" Camshaft Position — Timing Over-Retarded (Bank 1)P0341 — Camshaft Position Sensor "A" Circuit Range/Performance (Bank 1)

EVAP System

P0455 — EVAP System Leak Detected (Large Leak)P0442 — EVAP System Leak Detected (Small Leak)P0440 — EVAP System Malfunction (General)P0456 — EVAP System Leak Detected (Very Small Leak)

EGR System

P0401 — EGR Insufficient Flow DetectedP0402 — EGR Excessive Flow Detected

Cooling System

P0128 — Coolant Thermostat (Below Regulating Temperature)P0118 — Engine Coolant Temperature Sensor Circuit HighP0117 — Engine Coolant Temperature Sensor Circuit Low

Transmission

P0700 — Transmission Control System MalfunctionP0500 — Vehicle Speed Sensor (VSS) Malfunction

Network & Communication

U0100 — Lost Communication With ECM/PCM "A"

More codes are published regularly, prioritized by real-world fault frequency.