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P0666 is a diagnostic trouble code (DTC) for "PCM/ECM/TCM Internal Temperature Sensor Circuit". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
Either the powertrain control module (PCM), engine control module (ECM) or transmission control module (TCM) has detected an internal temperature malfunction in a related sensor. On many vehicles, the three modules are integrated into one unit, called the PCM.
A circuit failure has caused a potentially catastrophic overheating condition in a sensor.
Defective control module or shorted wiring to a module.
Individual control modules are designed with temperature sensors, that help with self-diagnosis and preservation in case of a malfunction. In some applications, the module that’s in failure mode may be easy to track down.
Begin diagnosis by testing the power and ground circuits for the module in question. Compare your findings with factory specs and make any repairs needed.
Clear any codes and retest the system. If all power and ground circuits are within spec, suspect a failed control module. Remember that replacing a control module will also require you to reprogram it for the vehicle.
Often, multiple control modules can fail along with the shorted or defective ground wiring to the first module in question.
In most cases, a P0666 code can be enough to prevent a vehicle from running at all.
Replacement of the failed module, or multiple failed modules.
Newer vehicles are equipped with Controller Area Network (CAN) bus systems. These discrete networks of micro-controllers govern everything such as:
These sophisticated networks can include as many as 20 different processors and micro-controllers, and can be very difficult to service by anyone other than a qualified tech with a specialized scanner such as an Autohex.
A misplaced probe from a digital volt/ohmmeter can be enough to wipe out a controller or even a whole line of controllers, requiring the entire vehicle to be reprogrammed. Should you elect to take this job on yourself, it’s important to have a memory saving device of some sort for backup in case of a system meltdown.
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.