DTC 23

Code Chart 23:

IAT Wiring Circuit:

CIRCUIT DESCRIPTION:
The IAT sensor uses a thermistor to control the signal voltage at the 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 terminal "GF16" voltage will be high. If the air is warm the sensor resistance is low, therefore the ECM terminal "GF16" voltage will be low.

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 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 5 volts return CKT 452 is open.

DIAGNOSTIC AIDS:
^ A "Scan" tool displays temperature of the air entering the engine, which should be close to ambient air temperature when engine is cold, and rise as underhood temperature increases.
^ A faulty connection, or an open in CKT 472 or CKT 469 can result in a Code 23.
^ Codes 23 and 34 stored at the same time, could be the result of an open CKT 469. The "Temperature to Resistance Values" scale in the chart above may be used to test the IAT sensor at various temperature levels to evaluate the possibility of a "slewed" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.
^ - Intermittent Malfunctions