DTC 23

Intake Air Temperature (IAT) Sensor Circuit Diagram:

CIRCUIT DESCRIPTION:
The IAT sensor is a thermistor with a negative temperature coefficient (as temperature increases, resistance decreases.) The PCM applies a 5 volt reference voltage through a resistor, to the sensor, on CKT 472, and then monitors the voltage in the circuit. When the air is cold, the sensors resistance is high, and the circuit voltage remains high (near reference voltage.) If the air is warm, sensor resistance decreases, causing drop in the measured voltage in the circuit. The PCM measures the voltage and calculates the temperature of the incoming air.

Code 23 will set when the following conditions exist:

^ Signal voltage indicates intake air temperature below -35 C (-31 F) for 4 seconds. Due to the conditions necessary to set a Code 23, the "SERVICE ENGINE SOON" light will only stay "ON" while the fault is present.
^ Time since engine start is 4 minutes or more.
^ Vehicle speed is less than 1 mph.
^ Start-up coolant temperature is less than or equal to -35 C (-31 F).
^ All conditions exist for 10 seconds.

TEST DESCRIPTION

Code 23 Diagnostic Chart:

Numbers below refer to circled numbers on the diagnostic chart.


1. A code 23 will set, due to an open sensor, wire, or connection. An open circuit would cause the scan tool to display approximately -40 C (-40 F). This test determines if the PCM is receiving a signal necessary for this code to set.
2. This step determines if the wiring to the PCM is OK, and if the PCM is reading the circuit.
3. There is an open circuit. This step determines if the open is in circuit 472 or circuit 808, or if the problem is a faulty PCM ground or PCM.

DIAGNOSTIC AIDS:

^ Poor Connection or Damaged Harness. Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent Test. If connections and harness check OK, monitor circuit voltage with "SCAN" tool, while moving related connectors and wiring harness. If the failure is induced, the display will change. This may help to isolate the location of the malfunction.