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 Temp Too Lo: Notes
The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors 4-6 volts on circuit No. 472 to the sensor. When manifold is cold, the sensor resistance is high, therefore, the ECM will see a high monitored voltage. As the air warms, the sensor resistance becomes less and the monitored voltage drops. Code 23 will set if engine has been running for more than 2 minutes and signal voltage indicates MAT temperature less than -22°F (-30°C).
- This test checks to see if Code 23 is the result of a hard failure or an intermittent condition.
- This test simulates conditions for a Code 25. If "Scan" tester displays a high temperature, ECM and wiring are okay.
- This test checks continuity of circuits No. 472 and 469. If circuit No. 469 is open there may also be a Code 33.
NO RELATED
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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.