DTC 23

Code 23 - Manifold Air Temperature Sensor:

Wiring Diagram for Manifold Air Temperature Sensor:

CODE 23 - MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)

Circuit Description:


The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM applies a voltage (about 4-6 volts) on CKT 472 to the sensor, When the air is cold the sensor (thermistor) resistance is high, therefore, the electronic control module (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:

^ A signal voltage indicates a manifold air temperature below -25~C (-13~F) for 3 seconds.

^ Time since engine start is 1 minute

^ OR

^ Engine not running

^ MAT temperature less than -25~C (-13~F)

^ No Code 15

^ Coolant temperature reading greater than -26~C (-15~F)

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 469 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.

Inspect CKTs 472 & 469 for intermittent opens. If Code 33 is also set carefully inspect CKT 469.

Refer to "Intermittents" in Diagnosis By Symptoms - No Trouble Codes Stored.