Toyota & Lexus fault codes
Toyota and Lexus engines are famously durable, but their emissions monitors run tight, so high-mileage Camry, Corolla, RAV4, Tacoma and Highlander owners see a predictable set of codes as sensors and catalytic converters age. The good news: most are sensor- or maintenance-level fixes rather than engine failures, as long as you diagnose with live data before replacing parts.
Toyota-specific diagnostic tips
- Toyota's catalyst monitor is strict, so cheap aftermarket converters frequently re-trigger P0420/P0430. An OEM/Denso or premium CARB-compliant converter is the reliable fix.
- Stick with Denso or NGK (the factory suppliers) for oxygen sensors, coils and plugs. Off-brand sensors and coils are a common cause of repeat codes on Toyota and Lexus.
- On the 2AZ-FE four-cylinder (2007-2011 Camry, RAV4 and Scion tC), oil consumption can foul plugs and skew fuel trims, so check the oil level before chasing misfire or lean codes.
- Always scan for every stored code and read live fuel-trim and O2 data first. A single lazy rear oxygen sensor often masquerades as an expensive converter.
In-depth Toyota code guides
Hand-researched, Toyota-specific diagnosis, costs and fixes.
P0171 on Toyota & Lexus: System Too Lean — Causes, Fixes & Cost
Toyota & Lexus
P0300 Random Misfire on Toyota & Lexus: Causes, Fixes & Cost
Toyota & Lexus
P0420 on Toyota & Lexus: Causes, Fixes & Cost
Toyota & Lexus
P0440 EVAP System Malfunction on Toyota & Lexus: Causes, Fixes & Cost
Toyota & Lexus
Common codes on Toyota & Lexus
Generic OBD-II codes our guides flag as common on Toyota vehicles.
Left Front Wheel Speed Sensor Circuit
Intake Camshaft Timing Over-Advanced (Bank 1)
Exhaust Camshaft Timing Over-Advanced (Bank 1)
Intake Air Temperature (IAT) Sensor Circuit High
Engine Coolant Temperature (ECT) Sensor Circuit High
Coolant Thermostat Below Regulating Temperature
O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
O2 Sensor Slow Response (Bank 1, Sensor 1)
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
System Too Lean (Bank 1)
System Too Rich (Bank 1)
System Too Lean (Bank 2)
System Too Rich (Bank 2)
Cylinder 1 Misfire Detected
Cylinder 2 Misfire Detected
Cylinder 3 Misfire Detected
Cylinder 4 Misfire Detected
Cylinder 5 Misfire Detected
Cylinder 6 Misfire Detected
Knock Sensor 1 Circuit Low (Bank 1)
Crankshaft Position Sensor Circuit Malfunction
Exhaust Gas Recirculation (EGR) Flow Insufficient
Secondary Air Injection System Incorrect Flow
Catalyst System Efficiency Below Threshold (Bank 1)
Catalyst System Efficiency Below Threshold (Bank 2)
EVAP System Malfunction
EVAP System Small Leak Detected
EVAP Vent Control Circuit Malfunction
EVAP System Large Leak Detected
EVAP System Very Small Leak Detected
EVAP Leak Detected (Loose/Faulty Fuel Cap)
Idle Air Control (IAC) System Malfunction
Idle Air Control System RPM Lower Than Expected
Idle Air Control System RPM Higher Than Expected
System Voltage High
Torque Converter Clutch Circuit Malfunction
Post-Catalyst Fuel Trim System Too Lean (Bank 1)
O2 Sensor Signal Stuck Lean (Bank 1, Sensor 1)