452 7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS
IAT Circuit Operation
Figure 457 IAT circuit diagram
The IAT sensor is supplied with a 5 V reference
signal at Pin 1 through 12–pin connector (Pin 5) from
ECM Pin X1–7. The sensor is grounded at Pin 2
through the signal ground at ECM Pin X4–24. As the
air temperature increases or decreases, the sensor
changes resistance and provides the air temperature
signal voltage at the ECM. The signal voltage is
monitored by the ECM to determine the intake air
temperature.
Fault Detection / Management
When the ECM detects an IAT signal out of range high
or low, the ECM will ignore the IAT signal and assume
an ambient temperature of 25 °C (77 °F).
IAT Diagnostic Trouble Codes (DTCs)
DTCs are read using the EST or by counting the
flashes from the amber and red ENGINE lamp on the
vehicle dash.
DTC 154
IAT signal out-of-range low
• DTC 154 is set by the ECM if signal voltage is less
than 0. 127 V for more than 0.35 second.
• DTC154canbesetduetoashorttogroundin
the sign al circuit or a failed IAT sensor.
• When DTC 154 is active, the amber ENGINE lamp
is illuminated.
DTC 155
IAT signal out-of-range high
• DTC 155 is set by the ECM if signal voltage is
more than 4.6 V for more than 0.35 second.
• DTC 155 can set due to an open signal or ground
circuit, a short to a voltage source, or a failed IAT
sensor.
• When DTC 155 is active, the amber ENGINE lamp
is illuminated.
Tools
• EST with MasterDiagnostics® software
• EZ-Tech® interface cable
• Digital Multimeter (DMM)
• 3-Banana Plug Harness
• 500 Ohm Resistor Harness
• Breakout Box
• Breakout Harness
• Terminal Test Adapter Kit
EGES-270-1
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
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