Intake Air Temperature (IAT) sensor uses a thermistor to control signal voltage to ECM. ECM applies voltage on Blue/Black wire to sensor. When intake manifold air is cold, sensor (thermistor) resistance is high and ECM senses high signal voltage. As intake air warms, sensor (thermistor) resistance decreases, and voltage drops.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Checks if Code 23 is due to a hard failure or an intermittent condition. Code 23 will set under the following conditions:
High temperature
- Engine has been running for longer than 2 minutes
- Signal voltage indicates IAT temperature is less than -36°F (-38°C).
Low temperature
- IAT temperature is greater than 390°F (199°C).
- Condition is detected for at least 2 minutes.
Simulates conditions for a Code 23 (high temperature indicated). If scan tester displays a high temperature, ECM and wiring are okay.
Checks continuity of Blue/Black and Black wires. If Black wire is open, Code 21 may also be present.

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.

Safety Warning

Code 23, IAT Sensor Circuit, High/Low Temperature Indicated: Notes

Use the Manual With the Right Hardware

When to See a Mechanic

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