AllFaultCodes: Instant Diagnostic Trouble Code (DTC) Decoder
Free technical database of automotive OBD-II / EOBD trouble codes (P, C, B, U) and HVAC heat pump / boiler error codes. Instant symptoms, causes, test steps & repair costs.
🔍 Instant Code Search & Decoder
Enter any OBD-II code (e.g. P0420, P0300, P0171, C1201, U0100) or HVAC error code (e.g. U4, F28, P8, EA):
🚗 Top Automotive Powertrain Codes (P0000 – P0999)
Engine, transmission, catalytic converter, and emissions diagnostic trouble codes:
🔴 P0420 — Catalyst System Efficiency Below Threshold (Bank 1)🔴 P0300 — Random or Multiple Cylinder Misfire Detected🔴 P0171 — System Too Lean (Bank 1)🔴 P0455 — Evaporative Emission Control System Leak Detected (Gross Leak)🔴 P0128 — Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)🔴 P0135 — O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)🔴 P0442 — EVAP System Small Leak Detected🔴 P0301 — DTC Code🔴 P0302 — DTC Code🔴 P0430 — DTC Code🔴 P0101 — DTC Code🔴 P0113 — DTC Code🔴 P0500 — DTC Code🔴 P0700 — DTC Code
❄️ Leading HVAC, Heat Pump & Boiler Error Codes
Diagnostic alert and lockout codes for Daikin, Mitsubishi, Vaillant, Worcester Bosch, Viessmann, Carrier, and NIBE:
❄️ Daikin U4 — Transmission Error Between Indoor and Outdoor Unit❄️ Vaillant F28 — Failure During Ignition / No Gas Supply❄️ Mitsubishi Electric P8 — Pipe Temperature Abnormality❄️ Worcester Bosch EA — Flame Not Detected❄️ Viessmann F4 — Burner Lockout (No Flame Signal)❄️ Carrier Code 33 — Limit Switch / Flame Rollout Open❄️ NIBE Alarm 51 — Low Brine Flow / Low Pressure
🚗 Browse OBD-II Codes by Vehicle Manufacturer
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🟡 Chassis (C-Codes) & 🔵 Network CAN-Bus (U-Codes)
🟡 C1201 — Chassis / ABS Sensor Code🟡 C1202 — Chassis / ABS Sensor Code🟡 C1233 — Chassis / ABS Sensor Code🟡 C1234 — Chassis / ABS Sensor Code🟡 C1235 — Chassis / ABS Sensor Code🟡 C1241 — Chassis / ABS Sensor Code🟡 C1242 — Chassis / ABS Sensor Code🟡 C1251 — Chassis / ABS Sensor Code🔵 U0100 — CAN Bus Communication Code🔵 U0101 — CAN Bus Communication Code🔵 U0102 — CAN Bus Communication Code🔵 U0104 — CAN Bus Communication Code🔵 U0121 — CAN Bus Communication Code🔵 U0140 — CAN Bus Communication Code🔵 U0155 — CAN Bus Communication Code🔵 U0199 — CAN Bus Communication Code