P0668
Control Module Internal Temperature Sensor A Circuit Low
Onboard computer / ECM
Generic OBD-II
High
What it means
P0668 means the control module (the ECM/PCM or TCM) has detected its own internal temperature sensor reading an abnormally low voltage. This sensor lets the module watch its own operating temperature. The fault is usually electrical — inside or around the module — rather than an engine problem, and it often has little effect on how the car drives.
High
Can I keep driving? Usually fine for short trips — this is an internal module monitoring fault, not an engine problem; have it checked if the car drops into limp mode.
Common symptoms
What you'll notice
- Check-engine light on, often with no obvious change in how the car drives
- Other control-module or sensor codes stored alongside it
- Possible reduced-power or limp mode if the module enters a protection strategy
- Rarely, cooling fans or other module-controlled outputs behaving oddly
Common causes
Most likely first
- Internal fault in the module's temperature sensor (built into the ECM/PCM/TCM)Likely
- Poor module ground or corroded/loose module connectorCommon
- Chafed or shorted wiring at the module harnessCommon
- Failed control moduleLess often
How to diagnose & fix
Work through it in order
- Scan for all stored codes and note freeze-frame; a low reading often points to a short-to-ground or ground fault.
- Inspect and clean the module's main connectors and ground straps.
- Check the module harness wiring for chafing or a short to ground.
- The sensor is internal, so if wiring and grounds are good the module is usually replaced or reprogrammed — confirm with the service procedure first. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0668?+
Usually yes for short trips — this is an internal monitoring fault, not a running problem. If the car drops into limp mode or shows temperature warnings, get it checked promptly.
Can I just clear P0668?+
You can, but if the internal sensor or a ground fault is still present it will return. Clearing does not repair the module or wiring.
Related codes
Often seen with P0668
Read & clear P0668 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX