Powertrain, generic · Computer and auxiliary outputs

P0668 Control Module Internal Temperature Sensor A Circuit Low

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. P0668 means the sensor signal is at the low voltage end: GM converts it into a temperature and treats −249 °C or less – a physically impossible value – for 60 s as a fault, with the lamp after two trips and the power-up temperature as substitute. 'Low' refers to the voltage; depending on the sensor type that need not mean a low temperature.

Likely causes

Module faulty internally (sensor or measuring circuit shorted)
Moisture or fluid in the electronics of the valve body
Module supply problem

Symptoms

  • Warning lamp
  • Changed shift quality (substitute value)
  • Scan tool shows an implausibly low module temperature

Repair estimate

DifficultyHardWorkshop job
Parts and labour€400–1,500
Time2–5 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

P0669P0667P0666P0634P0712

References: law.cornell.edu, gsi.ext.gm.com, saabwisonline.com.