Skip the auto shop - Our mechanics make house calls

P0668 OBD-II Trouble Code: PCM/ECM/TCM Internal Temperature Sensor Circuit Low

diagnostic check engine light

P0668 code definition

The P0668 code identifies a problematic and potentially harmful temperature reading from the engine or transmission via either the engine control module, the transmission control module, or the powertrain control module.

The P0668 code is often associated with the P0667 code.

What the P0668 code means

P0667 is the OBD-II generic code for a fault involving the internal temperature of the engine or transmission at the point where the sensor is located. Located within the engine and transmission are circuits that routinely check in on certain factors like heat and voltage at certain points. These relay the date back to the transmission control module and engine control module. In some cases, the information is also relayed to the powertrain control module. When the P0668 code is indicated, then one of the points in the circuit that is keeping track of the temperature inside of the engine or transmission that is getting a reading that is above or below what is required.

What causes the P0668 code?

The P0668 code has a number of common causes:

  • Faulty temperature sensor within the engine or transmission
  • Faulty wiring within the temperature sensor circuits
  • Overheating in the engine
  • Overheating in the transmission
  • Lack of coolant in the cooling system
  • Defective parts in the powertrain cooling systems

What are the symptoms of the P0668 code?

Since there are not many external indicators of excessive temperatures in the engine or transmission, the first indicator of a problem that would prompt the P0668 code is the Check Engine light on the dashboard. Since this trouble code is of a serious nature, the engine may stall once this code appears. The P0668 code is also capable of making the engine unable to start. If the engine remains running, then there may be sputtering or power loss.

How does a mechanic diagnose the P0668 code?

In most cases, the first step in diagnosis is to have a certified technician use an OBD-II scanner to read the trouble codes from the vehicle in real time. In the case of diagnosing a P0668 code, however, there is a high likeliness that there is an electrical problem and the circuits surrounding the affected circuit need to be tested with a voltmeter prior to any further diagnostics.

Once the electrical components surrounding the powertrain control module, engine control module, and transmission control module have been inspected, the trouble code can be reset by the technician. Once the code is reset, the vehicle will be taken for a test drive. If the code does not appear over the course of the drive, then it may have just been an electrical short or other intermittent issue.

If the code does appear during the test drive, then there is an issue that is causing excessive temperatures in the engine or transmission, and this issue could cause serious, catastrophic damage.

Common mistakes when diagnosing the P0668 code

The P0668 code is often misdiagnosed as a temperature problem within the engine or transmission when it is actually an electrical issue occurring within the circuit responsible for detecting the temperature. Failure can happen at the sensor itself, in the circuitry of the sensor, at the control module, or at any of the points in between. Sometimes the problem can be as simple as a loose connection.

How serious is the P0668 code?

The P0668 code has the potential to be extremely serious. In the worst cases, the P0668 code appears when there has been a catastrophic rise in temperature within the engine or transmission. In cases like these, the only viable repairs may involve rebuilding or even replacing the engine or transmission. The P0668 code has the ability to stop the engine and also the ability to render the vehicle unable to start. If this code appears, it should be assessed by a qualified technician as soon as possible.

What repairs can fix the P0668 code?

The most common repairs to address the P0668 code are as follows:

  • Replace faulty powertrain control module
  • Replace faulty engine control module
  • Replace faulty transmission control module
  • Replace faulty wiring harness
  • Repair or replace damaged sensor circuits
  • Replace or rebuild vehicle transmission
  • Replace or rebuild vehicle engine

Additional comments for consideration regarding the P0668 code

Before any parts are replaced, repaired, or rebuilt, all of the electrical connections and components within the affected area should be tested to ensure that the issue is not purely electrical.

Need help with a P0668 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance Related Trouble Codes: P2158: Vehicle Speed Sensor B P2160: Vehicle Speed Sensor B Circuit Low P2161:...


Related questions

Q: My Check Engine Light is on with a code for the engine control module

Unfortunately, without diagnosing the car using a scanning tool to download any potential trouble codes there is no way to tell what other codes may be causing this light to come on. There many different trouble codes that can also...

Q: Do all cars have an OBD system?

Virtually all vehicles from the 1987 model year to the present day have an OBD system. Some earlier model year vehicles, but not all, have some semblance of an OBD system. However, their diagnostic abilities are severely limited. There are...

Q: Trouble code P0060 after changing out all of my O2 sensors

Hello. Code P0060 comes on when the computer detects excessive resistance in the heater circuit for oxygen sensor 2, of bank 2. If all of the sensors have been replaced then it may be possible that the issue is rooted...