AutoCodes – Generic – P0666

P0666 Code - PCM/ECM/TCM Internal Temperature Sensor 'A' Circuit

Quick Answer

The control solenoid (w/body and TCM) valve assembly has a built-in TCM temperature sensor to detect possible overtemperature conditions of the Transmission Control Module (TCM). Common causes include Obstructions in the airflow of the radiator or transmission cooler, Kinked or damaged transmission fluid lines, Damage to the transmission cooler. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0666 indicates PCM/ECM/TCM Internal Temperature Sensor 'A' Circuit.
Common causes: Common causes include Obstructions in the airflow of the radiator or transmission cooler, Kinked or damaged transmission fluid lines, Damage to the transmission cooler.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 9,385

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on May 08, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P0666 Description

The control solenoid (w/body and TCM) valve assembly has a built-in TCM temperature sensor to detect possible overtemperature conditions of the Transmission Control Module (TCM). This fault indicates the TCM is in an overtemperature condition and the TCM has shut down to protect from possible heat damage to the TCM. TCM will remain off until the over temperature condition no longer exists.

OBDII Code P0666 - PCM/ECM/TCM Internal Temperature Sensor 'A' Circuit - AutoCodes.com — P0666 Code - PCM/ECM/TCM Internal Temperature Sensor 'A' Circuit

What does this mean?

What are the Possible Causes of the DTC P0666?

Obstructions in the airflow of the radiator or transmission cooler
Kinked or damaged transmission fluid lines
Damage to the transmission cooler

How to Fix the DTC P0666?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0666 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.