P-Codes

P0420 Code: Catalyst System Efficiency Below Threshold

P0420 means the engine computer sees that the catalytic converter on bank 1 is not cleaning exhaust as efficiently as expected. The converter may be worn, but exhaust leaks, oxygen sensor problems, misfires, or fuel mixture issues can also

P0430 Code: Catalyst System Efficiency Below Threshold Bank 2

P0430 means the engine computer believes the catalytic converter on bank 2 is not reducing exhaust pollutants well enough. On V-style engines, bank 2 is the side that does not contain cylinder 1. The code can come from the converter itself,

P0171 Code: System Too Lean Bank 1

P0171 means the engine computer is adding extra fuel because bank 1 is running lean. In plain terms, the engine is getting too much air, not enough fuel, or incorrect sensor information. Vacuum leaks, intake leaks, fuel delivery issues, and

P0174 Code: System Too Lean Bank 2

P0174 means bank 2 is running lean and the computer is adding fuel to compensate. It is common on V-style engines when unmetered air enters one side of the intake, fuel delivery is weak, or the mass airflow reading is inaccurate for the act

P0300 Code: Random or Multiple Cylinder Misfire

P0300 means the engine is misfiring randomly or across multiple cylinders instead of one clearly identified cylinder. Ignition, fuel, air leaks, compression problems, or timing issues can all interrupt combustion and trigger this code.

P0301 Code: Cylinder 1 Misfire Detected

P0301 means cylinder 1 is not burning its air-fuel mixture consistently. The problem may be isolated to that cylinder, such as a spark plug, coil, injector, compression issue, or local air leak near the intake runner.

P0302 Code: Cylinder 2 Misfire Detected

P0302 means cylinder 2 is misfiring enough for the engine computer to identify it. The cause may be electrical, fuel-related, mechanical, or an air leak that affects that cylinder more than the others.

P0303 Code: Cylinder 3 Misfire Detected

P0303 means cylinder 3 has a repeat misfire pattern. A technician will usually confirm the cylinder location, inspect ignition parts, check injector behavior, and rule out compression or valve problems before replacing parts.

P0304 Code: Cylinder 4 Misfire Detected

P0304 means cylinder 4 is not firing reliably. The code narrows the search to one cylinder, but the final cause still has to be separated between spark, fuel, air, compression, and wiring faults.

P0455 Code: Large EVAP System Leak Detected

P0455 means the fuel vapor system cannot hold pressure or vacuum during its self-test, and the leak appears large. A loose gas cap is a common simple cause, but hoses, valves, and the charcoal canister can also leak.

P0442 Code: Small EVAP System Leak Detected

P0442 means the evaporative emissions system detected a small vapor leak. The vehicle may drive normally, but the fuel vapor system is not sealing tightly enough during the onboard leak test.

P0440 Code: EVAP System Malfunction

P0440 is a broad EVAP system fault. Instead of identifying a specific leak size or valve circuit, the computer is saying the fuel vapor control system did not pass its expected self-test.

P0446 Code: EVAP Vent Control Circuit or Performance Fault

P0446 means the EVAP vent control system is not behaving as expected. The vent valve may be stuck, blocked, electrically faulty, or unable to seal the fuel vapor system during testing.

P0128 Code: Coolant Temperature Below Thermostat Regulating Temperature

P0128 means the engine is taking too long to reach the expected operating temperature. A thermostat stuck open is common, but low coolant, sensor readings, wiring, and fan behavior should be checked before parts are replaced.

P0011 Code: A Camshaft Position Timing Over Advanced Bank 1

P0011 means the intake camshaft timing on bank 1 is more advanced than the engine computer expected. Variable valve timing systems depend on clean oil, correct oil pressure, working solenoids, and accurate cam/crank signals.

P0014 Code: B Camshaft Position Timing Over Advanced Bank 1

P0014 means the exhaust camshaft timing on bank 1 is advanced beyond the expected range. Oil quality, VVT solenoid control, actuator movement, wiring, and mechanical timing all affect this code.

P0101 Code: Mass Air Flow Sensor Range or Performance Problem

P0101 means the mass airflow sensor signal does not match what the engine computer expects for current operating conditions. The sensor may be dirty or faulty, but intake leaks, wiring issues, and restricted airflow can create the same mism

P0135 Code: Oxygen Sensor Heater Circuit Bank 1 Sensor 1

P0135 means the heater circuit for the upstream oxygen sensor on bank 1 is not working as expected. The heater helps the sensor reach operating temperature quickly so the engine can control fuel accurately after startup.

P0401 Code: Exhaust Gas Recirculation Flow Insufficient

P0401 means the engine computer commanded EGR flow but did not see enough exhaust gas recirculation. Carbon buildup, valve problems, vacuum control faults, or sensor feedback issues can keep the system from flowing as expected.

P0402 Code: Exhaust Gas Recirculation Flow Excessive

P0402 means the engine computer believes too much exhaust gas is entering the intake through the EGR system. An EGR valve stuck open, control fault, or misleading sensor feedback can make the engine stumble because exhaust dilutes the air-f

P0507 Code: Idle Control System RPM Higher Than Expected

P0507 means the engine idle speed is higher than the computer is trying to command. Extra air entering the engine, throttle body buildup, idle control faults, or an idle relearn issue can all create a high idle condition.

P0700 Code: Transmission Control System Malfunction

P0700 means the transmission control module has reported a fault and asked the engine computer to turn on the check engine light. It is a pointer code, so the next step is reading the transmission module for the specific fault.

P0740 Code: Torque Converter Clutch Circuit Malfunction

P0740 means the computer sees a problem in the torque converter clutch control circuit or its expected operation. The clutch helps lock the converter at cruising speed for efficiency, so faults may affect shifting, heat, and fuel economy.

P0750 Code: Shift Solenoid A Malfunction

P0750 means the transmission computer detected a problem with shift solenoid A or the circuit that controls it. The solenoid helps route fluid pressure for gear changes, so faults can cause harsh shifts, wrong gear starts, or limp mode.

P1450 Code: Unable to Bleed Fuel Tank Vacuum

P1450 usually means the vehicle cannot relieve fuel tank vacuum as expected during EVAP operation. It is often associated with purge or vent control problems, a restricted vapor path, or a fuel tank pressure reading that does not change nor