P0666 Engine Trouble Code
What is P0666?
When P0666 code appears, first check your gas cap. Pull over safely, ensure it is tight, and inspect for cracks. A loose or damaged gas cap affects fuel-system pressure and emissions. A replacement cap costs about $3–$10. This simple fix can resolve the code and improve fuel economy.
Code Information
| Code Type: | OBD-II Powertrain (P) Trouble Code |
| System: | Powertrain |
| Code: | P0666 |
P0666 Symptoms
Check Engine Light
Illuminated dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration
Starting Problems
Difficulty starting the engine
P0666 Code Structure
Understanding what each digit means in the P0666 powertrain trouble code:
| P | 0 | 6 | 6 | 6 |
|---|---|---|---|---|
| Powertrain Code | Intake Valve Control Solenoid Circuit Low | Fuel Temperature Sensor B Circuit Range/Performance | Cylinder 4 Contribution/Balance Fault | Ignition Coil A Primary/Secondary Circuit Malfunction |
How to Fix P0666
Diagnostic Steps:
Oxygen sensors measure exhaust gas oxygen content to optimise air-fuel ratio. This optimisation improves fuel economy and reduces emissions. Sensors degrade over time and require periodic replacement.
Repair Solution:
Disconnected, dirty, or fouled spark plugs commonly prevent proper engine operation. Replace spark plugs every season or 25 hours. Verify proper spark plug gap. If plugs are good, check ignition components: spark plug wires, coils, and ignition module.
Technical Notes:
Parts or components should not be replaced based solely on P0666 DTC. Consult your vehicle service manual for proper diagnostic procedures, possible causes, and required testing before replacement.
P0666 Description
P0666 engine trouble code is related to Ignition Coil A Primary/Secondary Circuit Malfunction.
Main Cause
The primary reason for P0666 OBD-II Engine Trouble Code is: Fuel Temperature Sensor B Circuit Range/Performance.