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See how an example code breaks down:
System
Powertrain
Type
Generic
Subsystem
Emission control
Component
Catalyst
Specific fault
Efficiency below threshold
This breakdown is specific to code P0420. For other codes, the last three characters mean something different - a specific fault number from the SAE table.
Common faults for specific engines.
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Random/Multiple Cylinder Misfire Detected
Cylinder 1 Misfire Detected
Catalyst System Efficiency Below Threshold (Bank 1)
System Too Lean (Bank 1)
EVAP System Leak Detected (Small Leak)
EVAP System Leak Detected (Large Leak)
Coolant Temperature Below Thermostat Regulating Temperature
EGR Flow Insufficient
Turbocharger Underboost
Camshaft Position Sensor Circuit Malfunction
Crankshaft/Camshaft Position Correlation (Bank 1 Sensor A)
Camshaft Position Timing Over-Advanced (Bank 1)
Intake Air Temperature Sensor Circuit High
Mass Air Flow Sensor Range/Performance
Vehicle Speed Sensor Malfunction
Transmission Control System Malfunction
System Voltage Low
Fuel Rail/System Pressure Too Low
Fuel Pressure Regulator Control Circuit Low
Glow Plug Module Control Circuit (Diesel)
Diesel Particulate Filter Efficiency Below Threshold
Turbocharger Overboost Condition
Lost Communication With ECM/PCM
Engine Control System Malfunction (ABS/VSC Interlock - Toyota/Lexus)
Cylinder-Specific Misfire (P0302, P0303, P0304, P0305, P0306)
Catalyst Efficiency Below Threshold (Bank 2)
System Too Lean (Bank 2)
Crankshaft Position Sensor Circuit Malfunction
Mass Air Flow Sensor Circuit Low
O2 Sensor Heater Circuit (Bank 1 Sensor 2)
Knock Sensor Circuit Malfunction
Idle Control System RPM Lower Than Expected
Torque Converter Clutch Circuit Performance
Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
Camshaft Position Timing Over-Advanced (Bank 2)
O2 Sensor Heater Circuit (Bank 1 Sensor 1)
MAP/MAF - Throttle Position Correlation
Fuel Pressure Regulator Performance
MAP/Barometric Pressure Circuit Range/Performance
Engine Coolant Temperature Circuit Range/Performance
Throttle Position Sensor Circuit Range/Performance
Throttle Position Sensor Circuit Low Input
O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
O2 Sensor Heater Circuit (Bank 1 Sensor 1)
O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
O2 Sensor Circuit Low Voltage (Bank 1 Sensor 3)
O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
System Too Rich (Bank 1)
System Too Rich (Bank 2)
Fuel Temperature Sensor Circuit Range/Performance
Fuel Rail Pressure Sensor Circuit Low Input
Injector Circuit Malfunction Cylinder 1
Engine Overtemperature Condition
Fuel Pump Primary Circuit Malfunction
Turbocharger Wastegate Solenoid A Malfunction
Cylinder 2 Misfire Detected
Cylinder 3 Misfire Detected
Cylinder 4 Misfire Detected
Knock Sensor 1 Circuit Low Input (Bank 1)
Crankshaft Position Sensor Circuit Range/Performance
Crankshaft Position Sensor Circuit Low Input
Camshaft Position Sensor Circuit Range/Performance
Camshaft Position Sensor Circuit Low Input
Ignition Coil A Primary/Secondary Circuit Malfunction
Exhaust Gas Recirculation Flow Malfunction
Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Evaporative Emission Control System Malfunction
High Speed CAN Communication Bus
Lost Communication With TCM
Lost Communication With ABS Control Module
Lost Communication With Body Control Module
Lost Communication With Instrument Panel Cluster
Invalid Data Received From ECM/PCM
Left Front Wheel Speed Sensor Circuit
Right Front Wheel Speed Sensor Circuit
Left Rear Wheel Speed Sensor Circuit
Right Rear Wheel Speed Sensor Circuit
Driver Frontal Stage 1 Deployment Control (Airbag)
Driver Frontal Stage 2 Deployment Control (Airbag)
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Descriptions are for guidance only. Accurate diagnosis requires a workshop inspection.
