Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code 23 - Mat Sensor Temperature Low: Notes
The ECM supplies and monitors a voltage signal (4-6 volts) to the sensor through circuit No. 472. When temperatures are low, sensor resistance is high and the ECM will see a high monitored voltage signal. As temperatures increase, sensor resistance decreases and the voltage sensed by the ECM drops.
- This step checks to see if Code 23 is the result of a hard failure or an intermittent condition. Code 23 will set if the engine has been running for more than 58 seconds and the signal voltage indicates a MAT temperature less than -22°F (-30°C).
- Simulates conditions for a Code 25. If the "Scan" tester displays a high temperature, the ECM and wiring are not at fault.
- This step checks for continuity of circuits No. 472 and 469. If circuit No. 469 is open there may also be a Code 33 stored.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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