Skip the auto shop - Our mechanics make house calls

P0666 OBD-II Trouble Code: PCM/ECM/TCM Internal Temperature Sensor Circuit

Check Engine Light

P0666 code definition

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.

What the P0666 code means

A circuit failure has caused a potentially catastrophic overheating condition in a sensor.

What causes the P0666 code?

Defective control module or shorted wiring to a module.

What are the symptoms of the P0666 code?

  • Engine stalling
  • No-start condition
  • Stored code
  • Illuminated malfunction indicator lamp (MIL)

How does a mechanic diagnose the P0703 code?

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.

Common mistakes when diagnosing the P0666 code

Often, multiple control modules can fail along with the shorted or defective ground wiring to the first module in question.

How serious is the P0666 code?

In most cases, a P0666 code can be enough to prevent a vehicle from running at all.

What repairs can fix the P0703 code?

Replacement of the failed module, or multiple failed modules.

Additional comments for consideration regarding the P0666 code

Newer vehicles are equipped with Controller Area Network (CAN) bus systems. These discrete networks of micro-controllers govern everything such as:

  • Stability control
  • Traction control
  • Antilock brakes
  • Radio
  • Power windows
  • Cruise control

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.

Need help with a P0666 code?

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How Long Does a Fuel Filler Neck Last?
Getting gas from the pump to your gas tank is the only way to keep a car going. The fuel filler neck is a metal tube that is welded to the...
How to Find the Keyless Code on a Ford Explorer or Mercury Mountaineer
Many Ford Explorers and Mercury Mountaineers were manufactured with an option known as the Ford keyless entry keypad. Some models refer to it as SecuriCode as well. It...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...


Related questions

Q: Car is reading trouble code PO136 01/01

Hi. There could be a couple of things going on here. There are multiple oxygen sensors on your car and sometimes what we think bank 1 is may not be and the wrong oxygen sensor is replaced giving us the...

Q: Running problem

Discount parts are always suspect and I would never advise anyone to use them for this reason. I recommend purchasing a reputable part. An often missed problem with diagnosing the MAF sensor are vacuum leaks. MAF stands for (mass...

Q: Trouble code P0133 - 2002 Dodge Durango

Do you know if there are any exhaust leaks before the sensor? This code trips when the O2 sensor is not switching back an forth between rich and lean as fast as the computer is setting the conditions. This can...