Hummer H1 Service Manual page 1104

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DTC P0126 Engine Coolant Temperature (ECT) Insufficient for Stable Operation
C
5 VOLT
REFERNCE
CKP
SENSOR
SIGNAL
A
C5
B9
C29-A5 C29-B12
CKP
SENSOR
SIGNAL
Circuit Description
While the engine is warming, the PCM monitors the ECT sen-
sor to determine how long it takes the engine to reach the cool-
ant temperature required for "Closed Loop" operation. DTC
P0126 will set if the PCM determines that the engine does not
reach "Closed Loop" temperature in a specified amount of
time. This test will not run if either the intake air or engine
coolant temperature is too low at start up. The PCM will only
run this DTC on a cold start and only once per cold start.
Conditions for Running the DTC
• The PCM performs this DTC diagnostic once per igni-
tion cycle until a pass or fail condition exists.
• The engine operation time is greater than 600 seconds
• The DTCs P0112, P0113, P0117 and P0118 are not set.
• The engine coolant is less than 56˚C (133˚F).
• The intake air temperature is greater than -7˚C (20˚F)
or
• The engine operation time is greater than 300 seconds
• The DTCs P0112, P0113, P0117, and P0118 are not set.
• The engine coolant temperature is less than 56˚(133F).
• The intake air temperature is greater than -7˚C (22˚F).
05745159
CRANK
SHAFT
POSITION
SENSOR
(CKP)
SENSOR
GROUND
B
B
B11 B12
C27-D13 C27-C14
SENSOR 5 VOLT BOOST
GROUND REFERENCE SENSOR
SIGNAL
PCM/Tech 1 Scan Tool 38.1
C
BOOST/
A
BARO
PRESSURE
SENSOR
A
B
651 BK
C4
B10
C27-C11 C27-C1
ECT SENSOR
SENSOR GROUND
SIGNAL
Conditions for Setting the DTC
• The fuel burned since start up is greater than 1,000,000 cu. mm.
• The total idle time since start up is less than 450 seconds.
• The fuel burned since start up is greater than 468,120 cu.mm.
• The total idle time since start up is less than 225 seconds.
Action Taken When the DTC Sets
• The PCM illuminates the Malfunction Indicator Lamp
(MIL) on the second consecutive drive trip that the diag-
nostic runs and fails.
• The PCM records the operating conditions at the time
the diagnostic fails. The first time the diagnostic fails,
the "Failure Records" will store this information. If the
diagnostic reports a failure on the second consecutive
drive trip, the "Freeze Frame" records the operating
conditions at the time of failure and updates the "Failure
Records".
Conditions for clearing the MIL/DTC
• The PCM will turn the MIL off after three consecutive
drive trips that the diagnostic runs and does not fail.
• A last test failed (Current DTC) will clear when the ig-
nition is cycled and the diagnostic runs and does not fail.
ENGINE
COOLANT
TEMP
SENSOR
(ECT)
INTAKE AIR
TEMPERATURE
SENSOR (IAT)
A
B
C5
B5
C27-C4
IAT
POWERTRAIN
SENSOR
CONTROL
SIGNAL
MODULE
9-S12-066
3-1-01