Hummer H1 Service Manual page 1090

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DTC P0112 Intake Air Temperature (IAT)
Sensor Circuit Low Voltage
Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor that
controls signal voltage to the PCM. When the air is cold, the
sensor resistance is high, therefore the PCM will see a high sig-
nal voltage. As air warms, sensor resistance becomes less and
voltage drops.
Conditions for Setting the DTC
• Engine coolant temperature less than 42.5°C (109°F).
• Intake air temperature greater than or equal to 151°C
(303°F).
• Conditions met for 2 seconds.
Action Taken When the DTC Sets
A possible poor performance problem may exist during cold
weather operation.
Conditions for Clearing the MIL/DTC
• The PCM will turn the MIL off after three consecutive
trips without a fault condition.
• A History DTC will clear when forty consecutive
warm-up cycles that the diagnostic does not fail (coolant
temperature has risen 5°C (40°F) from start up coolant
temperature and engine coolant temperature exceeds
160°F (71°C) that same ignition cycle).
• Use of a Scan Tool
05745159
C
CRANK
5 VOLT
SHAFT
REFERNCE
POSITION
SENSOR
(CKP)
CKP
SENSOR SENSOR
SIGNAL GROUND
A B
C5-B5 C5-B12
C5-B9
C29-A5 C27-C1 C27-D13 C27-C14
CKP SENSOR 5 VOLT BOOST
SENSOR GROUND REFERENCE SENSOR
SIGNAL SIGNAL
C
BOOST/
A
BARO
PRESSURE
SENSOR
B A
B
C5-B10
359 BK
C5-C5
C5-B11
TO
TFT
SENSOR
C29-B12
SENSOR IAT
GROUND SENSOR
SIGNAL
Diagnostic Aids
Check harness routing for a potential short to ground in the sig-
nal circuit. Scan Tool displays intake air temperature in de-
grees centigrade. Refer to "Intermittents" on page 13. A
"skewed" sensor could result in poor driveability complaints.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic
Table.
3. This step determines if P0112 is a hard failure or an intermit-
tent condition.
4. This test will determine if the PCM can recognize an open
sensor.
5. This step will determine if the problem is a short to ground
or a malfunctioning PCM.
PCM/Tech 1 Scan Tool 25
INTAKE AIR
TEMPERATURE
SENSOR (IAT)
A
ENGINE
COOLANT
TEMP
SENSOR
(ECT)
B
C5-C4
ECT
POWERTRAIN
SENSOR
CONTROL
SIGNAL
MODULE
9-S12-066