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, Manifold Air Temperature (Mat) Sensor (Temperature Too Low): Notes
The MAT sensor uses a thermistor type resistor to control signal voltage to the ECM. A 4-6 volt reference signal is supplied to the sensor on circuit on circuit No. 472. When manifold air temperature is cold, sensor resistance is high and the ECM will see a high signal voltage. As the manifold air temperature increases, sensor resistance becomes less and voltage drops.
Test Number 1) This step checks if Code 23 is a result of a hard failure or an intermittent condition.
A Code 23 will set if:
- Signal voltage indicates a MAT temperature of less than -31°F (-35°C) with engine running longer then 2 minutes.
- With engine off, MAT reading is less than -31°F (-35°C) while the coolant temperature is greater than 15°F (-26°C).
Test Number 2) This test simulates conditions for a Code 25 (high MAT temperature). If the Scan tester displays a high temperature, the ECM and wiring are okay.
Test Number 3) This step checks continuity of circuits No. 472 and 452. If circuit No. 452 is open, there may also be a Code 33 set.
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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.