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 To Low: Notes
The manifold air temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies 4-6 volts on circuit No. 472 to the sensor. When manifold is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less and the voltage drops.
- This test checks to see if Code 23 is the result of a hard failure or an intermittent condition. Code 23 will be displayed if the engine is running for longer than 8 minutes, signal voltage indicates a MAT temperature less than -30°C or there is no VSS signal.
- This test simulates conditions for a Code 25. If the "SCAN" tester displays a high temperature, the ECM and wiring are okay.
- This test checks continuity of circuits No. 472 and 452. If circuit No. 452 is open there may also be a Code 21.
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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.