Hummer H1 Service Manual page 1096

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DTC P0118 Engine Coolant Temperature
(ECT) Sensor Circuit High 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, the sensor resistance
becomes less and the voltage drops. The voltage measured
across the thermister is interpreted as a temperature. This is a
type B DTC.
Conditions for Setting the DTC
• Engine running for at least 8 minutes.
• ECT less than -30°C (-22°F).
• Conditions met for 2 seconds
Action Taken When the DTC Sets
Idle increase
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
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
temperature and engine coolant temperature exceeds
71°C (161°F) that same ignition cycle).
• Use of a scan tool.
Diagnostic Aids
• Check harness routing for a potential short to ground.
After engine is started, the ECT temperature should rise
steady to about 85°C (185°F). A mis-scaled sensor
could result in poor driveability complaints.
Test Description
Number(s) below refer to number(s) on the diagnostic tables.
2. This test determines if PO 118 is an intermittent condition.
3. This test will determine if signal circuit is open, or a faulty
PCM.
PCM/Tech 1 Scan Tool 31
INTAKE AIR
TEMPERATURE
SENSOR (IAT)
A
ENGINE
COOLANT
TEMP
SENSOR
(ECT)
B
C5-C4
ECT
POWERTRAIN
SENSOR
CONTROL
SIGNAL
MODULE
9-S12-066