Hummer H1 Service Manual page 1106

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Test Description
Number(s) below refer to step numbers on the diagnostic table.
2. An ECT failure could cause a DTC P0126 to set, so
correct any ECT DTC that are set.
P
DTC 0126 Engine Coolant Temperature (ECT) Insufficient for Stable Operation
Step
1 Important: Before clearing any DTCs, use the scan tool
option "Capture Info" to save freeze frame and failure
records for reference, as the scan tool loses data when
using the "Clear Info" function.
2 Are any engine coolant temperature DTCs set?
3 a. Connect the scan tool.
b. Turn the ignition to the "RUN" position leaving
the engine off.
c. Disconnect the ECT sensor.
Does the scan tool indicate the ECT sensor is at a tempera-
ture colder than the specified value?
4 Using a jumper wire, jumper the terminals at the ECT sen-
sor harness connector together.
Does the scan tool indicate the ECT sensor is at a tempera-
ture colder than the specified value?
5 a. Reconnect the ECT sensor.
b. Start and idle the engine.
c. With the engine idling, observe the ECT sensor
display on the "Engine 1 Data List" option on the
scan tool.
Important: Allow time for the engine to warm up if it has
not already reached the specified temperature. 7 minutes is
the maximum amount of time it should take to reach this
temperature from a cold start. Less time should be neces-
sary if the engine is already warm.
Does the scan tool indicate the engine coolant temperature
has reached the specified value?
6 Using a Digital Multi Meter measure the resistance of the
DCT sensor. Refer to Temperature vs. Resistance.
Is the ECT resistance close to the value indicated in the
Temperature vs. Resistance Table
7 For an engine cooling system problem, check for the fol-
lowing conditions:
• Thermostat operation
• Coolant level
• Coolant to water ratio
• Cooling fan operation etc.
Refer to Engine Cooling.
Is the action complete?
8 Replace the ECT sensor. Refer to ECT Sensor Replace-
ment.
Is the action Complete?
05745159
Action
PCM/Tech 1 Scan Tool 38.3
6. If it is obvious that the engine is not reaching full
operating temperature, for example the radiator
hoses never get vary warm, or there is a complaint
of little or no heat from the heater, this step could
be skipped.
Value(s) Yes
––– Go to step 2.
––– Go to the applicable
DTC table.
-35˚C (-31˚F) Go to step 4
150˚C (302˚F) Go to step 5
60˚C (140˚F) System must be
rechecked on a cold
start. Refer to Diag-
nostic Aids.
___ Go to step 7.
___ Go to step 9.
___ Go to step 9.
No
Go to A Powertrain On
Board Diagnostic
(OBD) Systems Check
Go to step 3.
Go to the diagnostic
chart for P0117 Engine
Coolant Temperature
(ECT) Sensor Circuit
Low Voltage.
Go to the diagnostic
chart for DTC P0117
Engine Coolant Tem-
perature (ECT) sensor
Circuit Low Voltage.
Go to step 6.
Go to step 8.
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