OBD-II Fault Codes

Introduction The P0335 diagnostic trouble code indicates a failure in the circuit of the Crankshaft Position Sensor (CKP) “A”. The crankshaft position sensor monitors the speed and rotational position of the crankshaft, sending continuous data to the engine control unit (ECU). The ECU uses this crucial information to control ignition timing and fuel injection. Without […]

Introduction The P0505 diagnostic trouble code indicates a general fault within the Idle Air Control (IAC) system. The powertrain control module (PCM) uses the IAC valve to regulate engine idle speed by adjusting the amount of air bypassing the throttle plate. When the PCM detects that the actual idle speed does not match the target

Introduction The P0340 diagnostic trouble code indicates a malfunction in the circuit of the camshaft position (CMP) sensor. The powertrain control module (PCM) uses this sensor to monitor the rotational position of the camshaft, which determines fuel injector timing and ignition spark sequence. When the computer loses this signal or receives erratic data, it cannot

Introduction The P0135 diagnostic trouble code indicates a malfunction in the heater circuit of the upstream oxygen sensor (Bank 1, Sensor 1). Oxygen sensors need to reach a high operating temperature quickly to provide accurate air-fuel ratio data to the engine computer. An internal heating element inside the sensor ensures this happens rapidly upon cold

Introduction The P0440 diagnostic trouble code indicates a general malfunction within the vehicle’s Evaporative Emission Control (EVAP) system. The EVAP system prevents raw fuel vapors from escaping the fuel tank and venting into the atmosphere, routing them instead to the engine to be burned. A fault in this sealed network trips the check engine light

Introduction The P0101 OBD-II diagnostic trouble code indicates that the engine control unit (ECU) has detected a performance or range issue with the Mass Air Flow (MAF) sensor. The MAF sensor measures the volume of air entering the engine so the computer can calculate the correct amount of fuel. When the sensor’s signal falls outside

Introduction The P0401 diagnostic trouble code indicates that the powertrain control module (PCM) has detected insufficient flow through the Exhaust Gas Recirculation (EGR) system. This system reduces combustion temperatures by routing a portion of exhaust gases back into the intake manifold. Common Symptoms Primary Causes Step-by-Step Diagnosis & Fixes

Introduction The P0171 OBD-II code indicates that the engine’s air-fuel mixture is running too lean on Bank 1. This means there is either too much air or not enough fuel being injected into the combustion chambers. If left unaddressed, a lean condition can lead to engine overheating, valve damage, or melted pistons. Common Symptoms Primary

Introduction The P0420 diagnostic trouble code is one of the most frequent emissions-related issues reported by vehicle owners. It indicates that the catalytic converter’s efficiency has dropped below the factory threshold on Bank 1. In the US market, this code automatically triggers a failed smog check or emissions test. Common Symptoms Primary Causes Step-by-Step Diagnosis

Introduction The P0300 code is one of the most common and frustrating diagnostic trouble codes (DTCs) encountered by vehicle owners. It indicates that the powertrain control module (PCM) has detected random or multiple cylinder misfires. Unlike a single-cylinder misfire (like P0301 for cylinder 1), a P0300 points to a systemic issue affecting the entire engine.