DTC 23

Code 23 - Manifold Air Temperature (MAT) Sensor Circuit:

Wiring Diagram For Code 23 - Manifold Air Temperature (MAT) Sensor Circuit:

CODE 23 - MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT

Circuit Description:

The Manifold Air Temperature (MAT) Sensor is a thermistor that controls the signal voltage to the ECM.

The ECM applies a voltage (4-6 volts) on CKT 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. If the air is warm, the sensor resistance is low therefore the ECM will see a low voltage.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 23 will set if all conditions are met:

^ A signal voltage indicates a manifold air temperature below -30~C (-22~F) for 12 seconds.
^ Time since engine start is 1 minute or longer.
^ No VSS (vehicle not moving)

2. A Code 23 will set, due to an open sensor, wire, or connection. This test will determine if the wiring and ECM are OK.

3. This will determine if the signal CKT 472 or the 5V return CKT 452 is open.


Diagnostic Aids:

A "Scan" tool reads temperature of the air entering the engine and should read close to ambient air temperature when engine is cold, and rises as underhood temperature increases.

Carefully check harness and connections for possible open CKT 472 or 452.

See Diagnosis By Symptoms - No Trouble Codes Stored.

The "Temperature to Resistance Value" scale at the right may be used to test the MAT sensor at various temperature levels to evaluate the possibility of a "slewed" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.