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 23A - Mat Circuit (Low Temperature Indicated): Notes
Manifold Air Temperature (MAT) sensor uses a thermistor to control signal to ECM. ECM applies 4-6 volts to circuit No. D7 of sensor. When manifold air is cold, sensor resistance is high and ECM will see a MAT signal. As air warms, sensor resistance is low and MAT signal drops.
- Code 23A will set if engine has been running for longer than 3 minutes and signal voltage indicates a MAT temperature less than -40°F (-40°C).
- This simulates conditions for Code 23B. If Scan tester reads high temperature, ECM and wiring are okay.
- This checks continuity of circuits No. D2 and D7. If circuit No. D2 is open, Code 21A may also 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.
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