Powertrain Controls - ECM/PCM

Code 23 Chart:

Intake / Manifold Air Temperature Sensor Circuit:

CIRCUIT DESCRIPTION:

The Intake Air Temperature (IAT) 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.


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 10 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 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. A faulty connection, or an open in CKT 472 or 452 will result in a Code 23.