P0666
PCM/ECM/TCM Internal Temperature Sensor Circuit
- Severity
- Medium
- Driving
- Drivable — book it in
A fault in the module's internal temperature sensor circuit. The module cannot measure its own temperature, so it loses the ability to protect itself by reducing output when it gets hot. Nothing is necessarily overheating - the measurement has simply gone.
Possible causes
- CommonModule mounted where it gets little airflow, or a blocked cooling path
- CommonA shorted output making the module work far harder than it should
- CommonCorroded connector causing high resistance and local heating
- CommonFailed internal temperature sensor
- PossibleVery high ambient temperature combined with heavy load
- PossibleGenuine internal module failure
What you might notice
- Check engine light on
- Limp mode in some cases
- Often no symptom the driver notices
What to check, in order
- Read all codes. An over-temperature code alongside this one changes the picture entirely.
- Check the module connector for corrosion.
- This sensor is inside the module, so if the circuit really has failed the module is the repair - which makes it worth eliminating the supply voltage and connector first.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Computer output circuits and control module
P0600P0601P0602P0603P0604P0605P0606P0607P0608P0609P0610P0611P0612P0613P0614P0615P0616P0617P0618P0619P0620P0621P0622P0623P0624P0625P0626P0627P0628P0629P0630P0631P0632P0633P0634P0635P0636P0637P0638P0639P0640P0641P0642P0643P0644P0645P0646P0647P0648P0649P0650P0651P0652P0653P0654P0655P0656P0657P0658P0659P0660P0661P0662P0663P0664P0665P0666P0667P0668P0669P0670P0671P0672P0673P0674P0675P0676P0677P0678P0679P0680P0681P0682P0683P0684P0685P0686P0687P0688P0689P0690P0691P0692P0693P0694P0695P0696P0697P0698P0699