{"id":39393,"date":"2026-03-04T10:52:23","date_gmt":"2026-03-04T08:52:23","guid":{"rendered":"https:\/\/diagnozabam.ro\/sfaturi\/?page_id=39393"},"modified":"2026-03-04T11:44:51","modified_gmt":"2026-03-04T09:44:51","slug":"obd2-error-codes","status":"publish","type":"page","link":"https:\/\/diagnozabam.ro\/sfaturi\/obd2-error-codes\/","title":{"rendered":"OBD2 Error Codes"},"content":{"rendered":"

Modern vehicles use the OBD2<\/a> diagnostic system<\/strong> to monitor engine performance, emissions<\/a> and electronic systems. When a fault is detected, the car<\/a> stores a Diagnostic Trouble Code (DTC<\/a>)<\/strong> such as P0420<\/a>, P0171<\/a> or P0300<\/a>.<\/p>\n

On this page you will find the complete index of OBD2<\/a> error codes<\/a><\/strong>, along with explanations of how the diagnostic system works and links to detailed troubleshooting guides.<\/p>\n

DiagnozaBAM provides technical resources for drivers<\/a>, mechanics and automotive enthusiasts<\/strong> who want to understand vehicle diagnostics and fix problems faster.<\/p>\n

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What is an OBD2 Error Code<\/h1>\n

An OBD2<\/a> error code<\/strong> is a standardized diagnostic code generated by the vehicle’s Electronic Control Unit (ECU)<\/strong>.<\/p>\n

When the onboard system detects a malfunction, it stores a code and activates the Check Engine<\/a> Light<\/strong> on the dashboard<\/a>.<\/p>\n

These codes<\/a> help identify problems related to:<\/p>\n

engine performance
fuel system
emissions<\/a> components
sensors and electronic modules<\/p>\n

The stored codes<\/a> can be read using an OBD2<\/a> scanner connected to the diagnostic port of the vehicle<\/strong>.<\/p>\n

Example codes<\/a>:<\/p>\n

P0171<\/a> \u2013 System Too Lean
P0420<\/a> \u2013 Catalyst System Efficiency Below Threshold
P0300<\/a> \u2013 Random \/ Multiple Cylinder Misfire
P0087 \u2013 Fuel Rail Pressure Too Low<\/p>\n

Each code indicates a specific malfunction that requires further diagnosis.<\/p>\n

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OBD2 Code Structure Explained<\/h1>\n

All OBD2<\/a> diagnostic codes<\/a> follow a five-character format<\/strong>.<\/p>\n

Example:<\/p>\n

P0420<\/a><\/p>\n

Code structure:<\/p>\n

P \u2013 Powertrain system (engine \/ transmission<\/a>)
0 \u2013 Generic SAE diagnostic code
4 \u2013 Subsystem category
20 \u2013 Specific detected fault<\/p>\n

This structure allows technicians to quickly identify which system is affected and what type of problem occurred<\/strong>.<\/p>\n

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Types of OBD2 Diagnostic Codes<\/h1>\n

OBD2<\/a> codes<\/a> are divided into four main categories depending on the vehicle system involved.<\/p>\n

Powertrain Codes (Pxxxx)<\/h2>\n

Powertrain codes<\/a> refer to engine and transmission<\/a> systems<\/strong>, including fuel injection, ignition, air intake and emissions<\/a> components.<\/p>\n

Examples:<\/p>\n

P0100<\/a> \u2013 Mass Air Flow Sensor<\/a> Circuit
P0171<\/a> \u2013 System Too Lean
P0300<\/a> \u2013 Random Misfire Detected
P0420<\/a> \u2013 Catalyst Efficiency Below Threshold<\/p>\n

These are the most common diagnostic trouble codes<\/a><\/strong> found in modern vehicles.<\/p>\n

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Chassis Codes (Cxxxx)<\/h2>\n

Chassis codes<\/a> relate to systems responsible for vehicle stability, braking and suspension<\/strong>.<\/p>\n

Examples:<\/p>\n

C0035 \u2013 Wheel Speed Sensor Fault
C0040 \u2013 ABS Sensor Circuit Issue<\/p>\n

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Body Codes (Bxxxx)<\/h2>\n

Body<\/a> codes<\/a> are associated with interior and comfort systems<\/strong>.<\/p>\n

Examples include faults in:<\/p>\n

airbag systems
seat modules
climate control
lighting systems<\/p>\n

Example code:<\/p>\n

B0020 \u2013 Airbag Deployment Loop Fault<\/p>\n

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Network Codes (Uxxxx)<\/h2>\n

Network codes<\/a> indicate communication problems between electronic control modules<\/strong> inside the vehicle.<\/p>\n

Examples:<\/p>\n

U0100 \u2013 Lost Communication with ECM\/PCM
U0121 \u2013 Lost Communication with ABS Module<\/p>\n

These faults usually point to CAN bus communication issues or module failures<\/strong>.<\/p>\n

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Most Common OBD2 Error Codes<\/h1>\n

Some diagnostic trouble codes<\/a> appear much more frequently than others because they relate to typical engine problems.<\/p>\n

Common examples include:<\/p>\n

P0171<\/a> \u2013 Engine running too lean
P0300<\/a> \u2013 Random cylinder misfire
P0420<\/a> \u2013 Catalytic converter efficiency problem
P0128<\/a> \u2013 Coolant temperature below thermostat regulation
P0455<\/a> \u2013 Large EVAP leak detected<\/p>\n

Detailed diagnostic guides for each code are available in the articles listed below.<\/p>\n

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How to Diagnose an OBD2 Error Code<\/h1>\n

When a fault code appears, the diagnostic process usually follows these steps:<\/p>\n

Connect an OBD2<\/a> scanner to the vehicle diagnostic port.<\/p>\n

Read the stored diagnostic trouble codes<\/a> from the ECU.<\/p>\n

Identify the affected system such as fuel, ignition or emissions<\/a>.<\/p>\n

Inspect sensors and related components.<\/p>\n

Clear the code and verify if the fault returns.<\/p>\n

Accurate diagnosis often requires checking live sensor data and performing component tests<\/strong>.<\/p>\n

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OBD2 Diagnostic Articles<\/h1>\n

Below you will find detailed guides explaining individual OBD2<\/a> error codes<\/a>, including causes, symptoms and repair solutions.<\/p>\n

(New diagnostic articles are added regularly as part of the DiagnozaBAM technical knowledge base.)<\/p>\n

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