Car Error Codes (OBD-II)

Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter isn't cleaning exhaust gases efficiently enough on the driver's side of the engine.

P0171

System Too Lean (Bank 1)

The engine is getting too much air or too little fuel on the driver's side.

P0300

Random/Multiple Cylinder Misfire Detected

One or more cylinders are misfiring randomly, meaning fuel isn't igniting correctly.

P0455

Evaporative Emission System Leak Detected (Large Leak)

There's a significant leak in the fuel vapor containment system — most often just a loose or damaged gas cap.

P0128

Cooling

Coolant Temperature Below Thermostat Regulating Temperature

The engine isn't reaching its normal operating temperature, usually because the thermostat is stuck open.

P0442

Evaporative Emission Control System Leak Detected — Small Leak

There's a small leak in your car's fuel vapor system, often from a worn gas cap or a small crack in an EVAP hose.

P0430

Catalyst System Efficiency Below Threshold — Bank 2

The catalytic converter on the passenger side of the engine isn't working efficiently enough.

P0101

Mass Air Flow Sensor Circuit Range/Performance Problem

The mass airflow sensor is sending readings to the ECU that are outside the expected range for current driving conditions.

P0011

Intake Camshaft Position Timing Over-Advanced — Bank 1

The intake camshaft on the driver's side is advancing further than the ECU commanded it to.

P0500

Vehicle Speed Sensor Malfunction

The ECU isn't receiving a proper signal from the vehicle speed sensor.

P0700

Transmission

Transmission Control System Malfunction

The transmission control module has detected a fault and is alerting the powertrain control module.

P0401

Exhaust Gas Recirculation Flow Insufficient Detected

The EGR system isn't routing enough exhaust gas back into the engine as commanded.

P0301

Cylinder 1 Misfire Detected

Cylinder 1 isn't firing correctly — combustion isn't happening as it should in that specific cylinder.

P0302

Cylinder 2 Misfire Detected

Cylinder 2 isn't firing correctly — combustion is incomplete or absent in that specific cylinder.

P0303

Cylinder 3 Misfire Detected

Cylinder 3 is misfiring — that cylinder isn't completing combustion the way it should.

P0456

Evaporative Emission System Leak Detected — Very Small Leak

There's a very small leak in the fuel vapor system — even smaller than a P0442.

P0174

System Too Lean — Bank 2

The engine is running lean on the passenger side — too much air or not enough fuel on Bank 2.

P0122

Throttle Position Sensor/Switch A Circuit Low Input

The throttle position sensor is sending a voltage signal that's too low for what the ECU expects.

P0113

Intake Air Temperature Sensor 1 Circuit High Input

The intake air temperature sensor is sending a voltage signal that's higher than what the ECU expects, suggesting a cold or open circuit.

P0606

PCM/ECM Processor Fault

The car's main computer (the PCM or ECM) has detected an internal processing error.

P0135

O2 Sensor Heater Circuit Malfunction — Bank 1 Sensor 1

The heater element inside the upstream oxygen sensor on the driver's side isn't working properly.

P0141

O2 Sensor Heater Circuit Malfunction — Bank 1 Sensor 2

The heater inside the downstream oxygen sensor (after the catalytic converter) on the driver's side isn't working.

P0155

O2 Sensor Heater Circuit Malfunction — Bank 2 Sensor 1

The heater element in the upstream oxygen sensor on the passenger side isn't functioning correctly.

P0138

O2 Sensor Circuit High Voltage — Bank 1 Sensor 2

The downstream oxygen sensor on the driver's side is consistently showing high voltage, indicating it may be stuck or the engine is running rich.

P0325

Knock Sensor Circuit Malfunction — Bank 1

The knock sensor on the driver's side isn't communicating properly with the ECU.

P0102

Mass Air Flow Sensor Circuit Low Input

The mass airflow sensor is sending a voltage reading below the minimum threshold — the ECU thinks almost no air is entering the engine.

P0106

Manifold Absolute Pressure/BARO Sensor Range/Performance

The manifold absolute pressure sensor is sending readings that don't match what the ECU expects for current engine conditions.

P0117

Cooling

Engine Coolant Temperature Sensor Low Input

The engine coolant temperature sensor circuit voltage is lower than expected — the ECU thinks the engine is extremely hot.

P0118

Cooling

Engine Coolant Temperature Sensor High Input

The engine coolant temperature sensor is sending a higher voltage than expected — usually indicating an open circuit or a sensor that has failed to a 'cold' reading.

P0121

Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance

The throttle position sensor is sending a signal that's electrically valid but doesn't match what the ECU expects for current driving conditions.

P0123

Throttle/Pedal Position Sensor/Switch A Circuit High Input

The throttle position sensor is sending a higher voltage than the ECU expects, suggesting a wide-open throttle signal even when the pedal isn't pressed.

P0130

O2 Sensor Circuit Malfunction — Bank 1 Sensor 1

The upstream oxygen sensor on the driver's side isn't generating a proper signal — the circuit itself is at fault.

P0131

O2 Sensor Circuit Low Voltage — Bank 1 Sensor 1

The upstream oxygen sensor on the driver's side is consistently reading a low voltage, indicating a lean exhaust condition or a faulty sensor.

P0132

O2 Sensor Circuit High Voltage — Bank 1 Sensor 1

The upstream oxygen sensor on Bank 1 is stuck at a high voltage, suggesting a rich exhaust condition or a faulty sensor.

P0172

System Too Rich — Bank 1

The engine is getting too much fuel or too little air on the driver's side — the air/fuel mixture is running rich.

P0201

Injector Circuit/Open — Cylinder 1

The ECU detected a fault in the fuel injector circuit for cylinder 1 — the injector may not be firing or the circuit is open.

P0304

Cylinder 4 Misfire Detected

Cylinder 4 is not completing combustion properly — it's misfiring.

P0305

Cylinder 5 Misfire Detected

Cylinder 5 is misfiring — combustion is incomplete or absent in that cylinder.

P0306

Cylinder 6 Misfire Detected

Cylinder 6 is misfiring — combustion is failing in that specific cylinder.

P0335

Crankshaft Position Sensor A Circuit Malfunction

The crankshaft position sensor isn't sending a proper signal — this can prevent the engine from starting or running.

P0340

Camshaft Position Sensor A Circuit Malfunction — Bank 1

The camshaft position sensor on Bank 1 isn't sending a reliable signal to the ECU.

P0421

Warm Up Catalyst Efficiency Below Threshold — Bank 1

The Bank 1 catalytic converter isn't reaching full efficiency quickly enough during engine warm-up.

P0440

Evaporative Emission Control System Malfunction

The EVAP fuel vapor system has a general fault — the ECU detected something isn't working correctly in the system as a whole.

P0441

Evaporative Emission Control System Incorrect Purge Flow

The EVAP system isn't purging stored fuel vapors into the engine at the rate the ECU expects.

P0446

Evaporative Emission Control System Vent Control Circuit Malfunction

The EVAP vent valve circuit has a fault — the valve that allows fresh air into the charcoal canister isn't working properly.

P0505

Idle Control System Malfunction

The idle control system isn't maintaining the correct idle speed — the engine's idle is unstable or incorrect.

P0507

Idle Control System RPM High

The engine is idling faster than the ECU has commanded — typically caused by a vacuum leak or stuck-open idle bypass.

P0562

System Voltage Low

The ECU detected that the electrical system voltage is lower than it should be — typically from a weak battery or failing alternator.

P0740

Transmission

Torque Converter Clutch Circuit Malfunction

The torque converter clutch circuit has a fault — the lockup clutch inside the torque converter may not be engaging or releasing correctly.

P0750

Transmission

Shift Solenoid A Malfunction

Shift Solenoid A in the transmission isn't functioning correctly, which can cause incorrect or missed gear shifts.