Without Speed Density Update

Chart - Code 23 Manifold Air Temperature (Signal Voltage High):

Wiring Diagram for Manifold Air Temperature.:

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 5 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. The MAT Sensor is part of the Mass Air Flow (MAF) Sensor assembly so the ECM can accurately compensate the Air Flow reading based on temperature.

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 -35°C (-31°F) for 3 seconds.
- Time since engine start is 4 minutes or longer.
- No Vehicle Speed Sensor (VSS).
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 sensor 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. A faulty connection, or an open in CKT 472 or 452 will result in a Code 23. See "DIAGNOSIS BY SYMPTOMS." Testing and Inspection