Powertrain Controls - ECM/PCM

Code 23 Chart:

Code 23 Wiirng Diagram:

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 (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.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

1. Code 23 will set if:

- 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. The MAT sensor is difficult to reach and this test can be performed by disconnecting the MAT jumper harness connector. If the "Scan" indicates a temperature of over 130~C (266~F), the jumper harness to the sensor should be checked before replacing the sensor.

3. This will determine if the signal CKT 472 or the ground 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. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.