Powertrain, generic · Computer and auxiliary outputs

P0666 Control Module Internal Temperature Sensor A Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Control modules measure their own circuit board temperature with an internal sensor to protect output stages (overtemperature is P0634) and, in GM transmission modules, as a substitute for fluid temperature. In GM's 6T70/6T75 and related automatics the sensor sits in the transmission module inside the valve body, with no external wiring – so the repair is practically always the module or valve body assembly. P0666 is the general circuit fault of this sensor A. No manufacturer table available to us uses P0666 itself – GM splits the circuit faults into low (P0668) and high (P0669), plausibility is P0667. Expect a warning lamp and, in a transmission module, changed shift quality because a substitute temperature is used.

Likely causes

Module faulty internally (temperature sensor or measuring circuit)
Moisture or corrosion in the module or valve body
Supply or ground problems of the module

Symptoms

  • Warning or check engine light
  • Changed shift quality (substitute value)
  • Possibly transmission fluid temperature codes

Repair estimate

DifficultyHardWorkshop job
Parts and labour€300–1,500
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

transmission control modulecontrol module internal temperature sensor

Related codes

P0667P0668P0669P0634P0711

References: law.cornell.edu, saabwisonline.com.