DTC 23

CIRCUIT DESCRIPTION
The Manifold Air Temperature (MAT) Sensor uses a thermistor to control the signal voltage to the ECM. The Engine Control Module (ECM) applies a voltage (4-6 volts) on CKT 996 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.

Code 23 will set if:
^ A signal voltage indicates a manifold air temperature below -4O°C for 3 seconds.
^ Time since engine start is 8 minutes or longer.
^ No VSS.

Due to the conditions necessary to set a Code 23 the check engine light will only stay on when all three conditions are met.

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

2. If the resistance is greater than 25,000 ohms replace the sensor.