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CODE 23 MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT

Code Chart 23A:

MAT Sensor Circuit:

CIRCUIT DESCRIPTION:

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6V) on PPL/BLK wire to the sensor. When manifold air 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.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This step checks to see if Code 23A is the result of a hard failure or an intermittent condition. A Code 23A will set if:

a. Engine has been running for longer than 2 minutes.
b. Signal voltage indicates a MAT temperature less than -30°C.

2. This test simulates conditions for a Code 23B. If the Scan tool displays a high temperature, the ECM and wiring are OK.

3. This step checks continuity of PPL/BLK wire and BLK/WHT wire. If BLK/WHT wire is open, there may also be a Code 21.

DIAGNOSTIC AIDS:

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperatures may be checked with a Scan tool and should read close to each other. A Code 23A will result if PPL/BLK wire or BLK/WHT wire become open. If Code 23A is intermittent, Testing and Inspection