Honda & Acura fault codes
Honda and Acura engines are reliable but have their own signatures: oil leaking down the spark-plug tubes, VTEC/VTC oil-control quirks, and a couple of well-known fuel-injector service campaigns. On most, the fix is a plug, coil, sensor or injector rather than anything internal, provided you check for oil-fouling and confirm with live data.
Honda-specific diagnostic tips
- Oil in the spark-plug wells from a leaking valve-cover gasket or tube seals is a classic Honda misfire cause. If a plug is oil-fouled, fix the leak, not just the plug.
- Use OEM NGK or Denso plugs gapped to spec. Honda engines are sensitive to plug gap and to off-brand plugs.
- Some 2016-2019 1.5T Civic and CR-V engines had fuel-injector and oil-dilution service updates, so check for an extended warranty or software update before paying for injectors.
- For P0420, Honda and Acura often fail the rear oxygen sensor before the converter itself. Verify with live data first.
In-depth Honda code guides
Hand-researched, Honda-specific diagnosis, costs and fixes.
Common codes on Honda & Acura
Generic OBD-II codes our guides flag as common on Honda vehicles.
Engine Coolant Temperature (ECT) Sensor Circuit High
Insufficient Coolant Temperature for Closed Loop
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 Rich (Bank 1)
Random/Multiple Cylinder Misfire Detected
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)
Exhaust Gas Recirculation (EGR) Flow Insufficient
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
Torque Converter Clutch Circuit Malfunction
Torque Converter Clutch Performance / Stuck Off
Post-Catalyst Fuel Trim System Too Lean (Bank 1)