OBD2 Fault Code Database

Every code includes: structured diagnosis, probable causes ranked by frequency, and direct repair steps. No filler.

Popular Symptom Paths

Check Engine Light On Hard Start / No Start Poor Fuel Economy Rough Idle Power Loss ABS / Traction Warning

P — Powertrain

Code	Description	Severity	Category
P0171	System Too Lean (Bank 1)	medium	Fuel & Air Metering
P0300	Random / Multiple Cylinder Misfire	high	Ignition System
P0420	Catalyst System Efficiency Below Threshold (Bank 1)	medium	Catalyst System
P0128	Coolant Temperature Below Thermostat Regulating Temperature	low	Cooling System
P0442	Evaporative Emission System Leak Detected (Small Leak)	low	EVAP System
P0507	Idle Air Control System RPM High	medium	Idle Control
P0401	Exhaust Gas Recirculation Flow Insufficient Detected	medium	EGR System

B — Body

Code	Description	Severity	Category
B0020	Front Passenger Side Airbag Deployment Control	high	Airbag / SRS

C — Chassis

Code	Description	Severity	Category
C0035	Left Front Wheel Speed Sensor Circuit	high	ABS / Traction Control

U — Network / CAN Bus

Code	Description	Severity	Category
U0100	Lost Communication With ECM/PCM	high	CAN Bus