Hummer H2. Manual — part 1631

DTC P0128

Circuit Description

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the
powertrain control module (PCM) for engine control, and as an enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and used to determine if the vehicle has been driven within
conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If
the coolant temperature does not increase normally or does not reach the regulating temperature of the
thermostat, diagnostics that use ECT as enabling criteria, may not run when expected.

This DTC will only run once per ignition cycle within the enabling condition. If the PCM detects the calibrated
amount of air flow and engine run time have been met and the ECT has not met the minimum thermostat
regulating temperature, DTC P0128 sets.

Conditions for Running the DTC

z

DTCs P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0125, P0500, P0502, P0503 are not
present.

z

The start up engine coolant temperature is less than 70°C (158°F).

z

The intake air temperature (IAT) sensor parameter is between -7 and +55°C (+19 and +131°F).

z

The engine is running between 120-1,600 seconds.

z

The vehicle speed is more than 8 km/h (5 mph) for more than 2.5 km (1.5 miles).

z

The mass air flow (MAF) is between 20-75 g/s with the average more than 15 g/s.

z

This diagnostic has not previously run this ignition cycle.

Did you complete the replacement?

Go to Step 14

-

13

Replace the PCM. Refer to Powertrain Control
Module (PCM) Replacement .
Did you complete the replacement?

or

Go to Step 14

-

14

1. Clear the DTCs with a scan tool.

2. Turn OFF the ignition for 30 seconds.

3. Start the engine.

4. Operate the vehicle within the Conditions for

Running the DTC. You may also operate the
vehicle within the conditions that you
observed from the Freeze Frame/Failure
Records.

Did the DTC fail this ignition?

-

Go to Step 2

Go to Step 15

15

Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?

-

Go to Diagnostic

Trouble Code

(DTC) List

System OK

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

Conditions for Setting the DTC

The PCM detects all of the following conditions:

z

The calibrated amount of engine run time has been met.

z

The calibrated amount of engine air flow has been met.

z

The calibrated vehicle speed and distance have been met.

z

The calibrated minimum engine coolant temperature of 75°C (167°F) has not been met.

Action Taken When the DTC Sets

z

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition
cycle that the diagnostic runs and fails.

z

The control module records the operating conditions at the time the diagnostic fails. The first time the
diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic
reports a failure on the second consecutive ignition cycle, the control module records the operating
conditions at the time of the failure. The control module writes the operating conditions to the Freeze
Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

z

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles
that the diagnostic runs and does not fail.

z

A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

z

A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other
emission related diagnostic.

z

Clear the MIL and the DTC with a scan tool.

DTC P0128

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls Connector End Views or Powertrain Control
Module (PCM) Connector End Views

1

Did you perform the Diagnostic System Check-
Engine Controls?

-

Go to Step 2

Go to

Diagnostic

System Check -

Engine

Controls

2

Is the cooling system coolant low?

-

Go to Draining and

Filling Cooling

System in Engine

Cooling

Go to Step 3

3

Test and verify the proper operation of the
thermostat. Refer to Thermostat Diagnosis in
Engine Cooling.

-

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

Did you find and correct the condition?

Go to Step 14

Go to Step 4

4

1. Disconnect the engine coolant temperature

(ECT) sensor.

2. Inspect for the following conditions:

z

Corrosion on the ECT sensor terminals

z

Improper or corroded terminals at the
ECT harness connector

z

Loose terminals in the ECT harness
connector-Refer to Testing for
Intermittent Conditions and Poor
Connections and Connector Repairs
in Wiring Systems.

Did you find and correct the condition?

-

Go to Step 14

Go to Step 5

5

Measure the voltage from the signal circuit of the
ECT sensor to a good ground with a DMM. Refer
to Circuit Testing in Wiring Systems.
Is the voltage within the specified range?

4.8-5.2

V

Go to Step 6

Go to Step 8

6

Measure the voltage from the signal circuit of the
ECT sensor to the low reference circuit of the ECT
sensor with a DMM. Refer to Circuit Testing in
Wiring Systems.
Is the voltage within the specified range?

4.8-5.2

V

Go to Step 9

Go to Step 7

7

Test the ECT sensor low reference circuit for high
resistance. Refer to Circuit Testing and Wiring
Repairs in Wiring Systems.
Did you find and correct the condition?

-

Go to Step 14

Go to Step 11

8

Test the ECT sensor signal circuit for high
resistance. Refer to Circuit Testing and Wiring
Repairs in Wiring Systems.
Did you find and correct the condition?

-

Go to Step 14

Go to Step 11

9

1. Turn OFF the ignition.

2. Remove the ECT sensor. Refer to Engine

Coolant Temperature (ECT) Sensor
Replacement .

3. Place the sensor on a work surface away

from any heat source.

4. Allow the sensor to reach the ambient air

temperature for 30-60 minutes.

5. Observe and record the ambient air

temperature of the vehicle environment using
an accurate thermometer.

-

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

DTC P0131 OR P0151

Circuit Description

6. Measure the resistance of the ECT sensor and

record the value.

7. Compare the resistance measurement of the

ECT sensor to the ambient air temperature on
the Temperature vs. Resistance table. Refer
to Temperature vs Resistance .

Is the resistance measurement of the ECT sensor
within the specified range?

IMPORTANT:

Do not hold the ECT sensor by the probe.

Go to Step 10

Go to Step 12

10

Install the ECT sensor. Refer to Engine Coolant
Temperature (ECT) Sensor Replacement .
Is the action complete?

-

Go to Intermittent

Conditions

-

11

Test for an intermittent and for a poor connection at
the powertrain control module (PCM). Refer to
Testing for Intermittent Conditions and Poor
Connections and Connector Repairs in Wiring
Systems.
Did you find and correct the condition?

-

Go to Step 14

Go to Step 13

12

Replace the ECT sensor. Refer to Engine Coolant
Temperature (ECT) Sensor Replacement .
Did you complete the replacement?

-

Go to Step 14

-

13

Replace the PCM. Refer to Powertrain Control
Module (PCM) Replacement .
Did you complete the replacement?

-

Go to Step 14

-

14

1. Clear the DTCs with a scan tool.

2. Turn OFF the ignition for 30 seconds.

3. Start the engine.

4. Operate the vehicle within the Conditions for

Running the DTC. You may also operate the
vehicle within the conditions that you
observed from the Freeze Frame/Failure
Records.

Did the DTC fail this ignition?

-

Go to Step 2

Go to Step 15

15

Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?

-

Go to Diagnostic

Trouble Code

(DTC) List

System OK

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2