Hummer H1 Service Manual page 1094

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DTC P0117 Engine Coolant Temperature
(ECT) Sensor Circuit Low Voltage
CKP
SENSOR
SIGNAL
A
C29-A5
CKP
SENSOR
SIGNAL
Circuit Description
The engine coolant Temperature (ECT) sensor is a thermistor
that controls signal voltage to the PCM. When the engine is
cold, the sensor resistance is high, therefore the PCM will see
high signal voltage. As the engine warms, sensor resistance be-
comes less and voltage drops. The voltage measured across the
thermistor is interpreted as a temperature. This is a type B
DTC.
Conditions for Setting the DTC
Engine coolant temperature greater than or equal to 151°C
(303°F) for 2 seconds.
Action Taken When the DTC Sets
• High idle
• No TCC
• Shift schedules will be affected.
05745159
C
CRANK
5 VOLT
SHAFT
REFERNCE
POSITION
SENSOR
(CKP)
SENSOR
GROUND
B
B
C5-B5 C5-B12
C5-B9
C27-C1 C27-D13 C27-C14
SENSOR 5 VOLT BOOST
GROUND REFERENCE SENSOR
SIGNAL
C
BOOST/
A
BARO
PRESSURE
SENSOR
A
B
C5-B10
359 BK
C5-C5
C5-B11
TO
TFT
SENSOR
C29-B12
SENSOR IAT
GROUND SENSOR
SIGNAL
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
71°C (160°F) that same ignition cycle).
• Use of a Scan Tool.
Diagnostic Aids
Check harness routing for a potential short to ground. After en-
gine is started, the coolant temperature should rise steadily to
about 85°C (185°F). refer to "Intermittents" on page 14. A
"skewed" sensor could result in poor driveability complaints.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic
Table.
2. This step determines if P0117 is a hard failure or an inter-
mittent condition.
3. This test will check the PCM and the wiring.
PCM/Tech 1 Scan Tool 29
INTAKE AIR
TEMPERATURE
SENSOR (IAT)
A
ENGINE
COOLANT
TEMP
SENSOR
(ECT)
B
C5-C4
ECT
POWERTRAIN
SENSOR
CONTROL
SIGNAL
MODULE
9-S12-066