Powertrain Controls - ECM/PCM

Code 23:

CTS Circuit:

CIRCUIT DESCRIPTION:

The Intake Air Temperature (IAC) (previously MAT) sensor is a thermistor. The PCM applies a voltage (about 5.0 volts) on CKT 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore, the PCM will measure a high signal voltage. If the air is warm, the sensor resistance is low, therefore, the PCM will measure a low voltage.

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

Code 23 will set if:

^ Voltage at PCM terminal "BB7" indicates an intake air temperature below -34°C (-29°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.

1. A code 23 will set, due to an open sensor, wire, or connection. An open circuit would cause the Tech 1 to display approximately -40°C (-40°F). This test determines if the wiring and PCM are OK.

DIAGNOSTIC AIDS:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

^ Poor Connection or Damaged Harness - Inspect PCM harness connectors for backed out terminal "BA7/BB7," 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, observe ED23/Tech 1 IAT display while moving related connectors and wiring harness with warm engine running at part throttle in "Closed Loop." If the failure is induced, the IAT display may change to a -40°C temperature reading. This may help to isolate the location of the malfunction.