Powertrain Controls - ECM/PCM

Diagnostic Chart:

Electrical Schematic:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor (a variable resistor that changes along with outside air temperature changes) in series with a fixed resistor within the PCM. The IAT sensor measures the temperature of the air entering the intake manifold. The PCM applies 5 volts to the sensor. The PCM monitors the voltage across the IAT sensor and converts it into a temperature reading. When the outside air temperature is cold, the IAT sensor resistance is high. and when the outside air temperature is warm, the IAT sensor resistance is low. Therefore, when the air temperature is cold the PCM will receive a high voltage input, and when the air temperature is warm the PCM will receive a low voltage input.

DTC 24 will set if either of the following conditions are met for at least 0.5 seconds:
^ Voltage input at the PCM indicates a very low air temperature.
^ Voltage input at the PCM indicates a very high air temperature.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. This checks for an open or short to ground in the YEL/BLK wire between the PCM and IAT sensor and for a faulty PCM.
2. This checks for an open in the BRN wire between the PCM and the IAT sensor and for a faulty PCM.
3. This determines if the problem is a faulty IAT sensor or PCM.

DIAGNOSTIC AIDS
A "shifted" (mis-scaled) sensor could result in poor driveability complaints. Measure the resistance of the !AT sensor according to the diagnostic aids chart on the diagnostic chart. If DTCs 22, 31 and 41 are also set, the malfunction may be in the sensor ground circuit.

INTERMITTENT MALFUNCTIONS
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect hamess connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.