Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer is having trouble reading the temperature inside itself. It's like when a thermometer isn't working right and you can't tell how hot or cold it is.
The engine control module (ECM) uses an internal temperature sensor to monitor its operating temperature. Code P0668 indicates that the signal from this sensor is lower than expected.
The P0668 code is triggered when the ECM detects a low voltage signal from its internal temperature sensor. This sensor is crucial for monitoring the temperature to ensure the ECM operates within its optimal temperature range. A low circuit signal could indicate a problem with the sensor, wiring, or the ECM itself.
• Check Engine Light is on
• Engine may run poorly
• Possible reduced fuel efficiency
• Faulty internal temperature sensor
• Wiring issues or poor connections
• Faulty ECM
ECM: Engine Control Module
OBD-II: On-Board Diagnostics, Second Generation
• Use an OBD-II scanner to confirm the code.
• Inspect wiring and connectors for damage or corrosion.
• Test the internal temperature sensor for proper operation.
• Repair or replace damaged wiring or connectors.
• Replace the internal temperature sensor if faulty.
• Replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Screwdrivers
$200 - $800
Moderate
• Chevrolet Silverado
• GMC Sierra
• Ford F-150
• Regularly inspect and maintain ECM connections.
• Ensure proper vehicle cooling system maintenance.
• Avoid extreme temperature exposure to the vehicle.
Sensor Issue
• Have the vehicle inspected by a professional if the Check Engine Light is on.
• Avoid driving in extreme temperatures until the issue is resolved.
Check with your vehicle manufacturer, as ECM-related issues may be covered under powertrain warranty.
This code has been associated with issues in vehicles with aging ECMs or those exposed to extreme temperature conditions.
Moderate – It should be addressed soon to prevent potential engine performance issues.
Driving with a malfunctioning ECM can lead to increased emissions and potential engine damage.
• Vehicle at operating temperature
• Stable electrical system voltage
The internal temperature sensor is located within the ECM itself.
Q: Can I drive with a P0668 code?
A: It's possible to drive short distances, but it's best to have it checked soon to avoid potential engine issues.
Q: How do I reset the P0668 code?
A: After repairs, use an OBD-II scanner to clear the code, but ensure the issue is fixed first.
High-End · Full-system diagnostics
A full-system bidirectional platform aimed at advanced DIY users and professional diagnostic workflows.
Network faults often require full-system access instead of a generic code reader alone.
View on Amazon
Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
View on Amazon
Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.