P0668 code meaning
Control Module Internal Temperature Sensor A Circuit Low
Powertrain system Generic code P06xx codes Check engine light
What P0668 means
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.
P0668 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor2 to 5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0668
- Warning lamp
- Changed shift quality (substitute value)
- Scan tool shows an implausibly low module temperature
Common causes of P0668
- Most likelyModule faulty internally (sensor or measuring circuit shorted)
- PossibleMoisture or fluid in the electronics of the valve body
- Less likelyModule supply problem
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission control moduleControl module internal temperature sensor
What each part of P0668 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 68 | The exact fault in that area. |
What to do next
- Note P0668 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0668
What does P0668 mean?
P0668 means "Control Module Internal Temperature Sensor A Circuit Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0668?
Drive gently and only to a workshop. With P0668 the car can go into limp mode (reduced power) to protect itself.
Will P0668 fail an emissions test?
Yes, it can. P0668 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0668 to fix?
Difficulty: hard. A typical repair takes 2 to 5 hours of work. This is a job for a workshop.
Will P0668 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.