Hummer H1 (2006+). Instruction - page 66

OBD-108

On-Board Diagnostics

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DTC P0181 Fuel Temperature Sensor Performance (Figure OBD-32)

Figure OBD-32: Fuel Temperature Sensor Circuit

Circuit Description

The fuel temperature sensor is a thermistor. The engine control module (ECM) supplies the fuel temperature sensor a reference
voltage of 5 volts on the signal circuit and also provides a low reference circuit to the sensor. When the fuel temperature sensor is
cold, the resistance is high. The fuel temperature sensor signal voltage remains near the supplied voltage cold and decreases the
signal voltage as the sensor warms. The control module monitors the fuel temperature sensor signal circuit in order to calculate the
temperature of the fuel entering the engine.

Conditions for Setting the DTC

• The fuel temperature and the ECT are more than 9.75°C (18°F) of each other at start-up.

• The IAT has dropped less than 5.25°C (10°F) after running more than 400 seconds above 24 km/h (15 mph).

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diag-

nostic runs and fails.

• 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 consecu-
tive 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.

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On-Board Diagnostics OBD-109

5745804

Conditions for Clearing the MIL/DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic

runs and does not fail.

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

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

diagnostic.

• Clear the MIL and the DTC with a scan tool.

Step

Action

Value(s)

Yes

No

1

NOTE: Before clearing DTC(s) use the scan tool “Capture info”
to record Freeze Frame and Failure Records for reference, as data
will be lost when “Clear Info” function is used

Was the “On-Board Diagnostic (OBD) System Check” per-
formed?

Go to step 2.

Go to OBD Sys-

tem Check.

2

1.

Allow the engine to cool to ambient temperature.

2.

Turn ON the ignition.

3.

Observe the intake air temperature (IAT) sensor parameter
with a scan tool.

Does the scan tool indicate a temperature near ambient tempera-
ture within the specified range?

10°C

(18°F)

Go to Step 3

Go to Step 4

3

1.

Start the engine.

2.

Operate the vehicle within the Conditions for Running the
DTC as specified in the supporting text.

Does the DTC fail this ignition?

Go to Step 6

Intermittent Go

To Diagnostic

Aids

4

1.

Disconnect the mass air flow (MAF) sensor connector.

2.

Turn ON the ignition, with the engine OFF.

3.

Measure the voltage of the IAT signal circuit 654 (DB) at the
MAF sensor connector.

Does the voltage measure near the specified value?

5 V

Go to Step 5

Go to Step 9

5

1.

Connect a test lamp to B+.

2.

Probe the low reference circuit 250 (BK) of the IAT.

Does the test lamp illuminate?

Go to Step 14

Go to Step 11

6

1.

Disconnect the air filter outlet duct to access the fuel temper-
ature sensor.

2.

Disconnect the fuel temperature sensor electrical connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Probe the fuel temperature sensor signal circuit 324 (YL)
with a DVOM connected to ground.

Does the voltage measure near the specified value?

5 V

Go to Step 8

Go to Step 9

7

Connect a 3-amp fused jumper wire between the fuel temperature
sensor signal circuit 324 (YL) and ground.

Is the temperature more than the specified value?

140°C

(285°F)

Go to Step 8

Go to Step 10

8

1.

Connect a test lamp to B+.

2.

Probe the low reference circuit 252 (BK) pin A of the fuel
temperature sensor connector.

Does the test lamp illuminate?

Go to Step 15

Go to Step 11

OBD-110

On-Board Diagnostics

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9

1.

Turn OFF the ignition.

2.

Disconnect the engine control module (ECM) connectors.

3.

Inspect the signal circuit 324 (YL) for an open or for short to
ground between C76 pin 27 and pin B of the FT sensor.

Did you perform a repair?

Go to Step 16

Go to Step 12

10

Repair the high resistance in the fuel temperature sensor signal
circuit 324 (YL).

Did you complete the repair?

Go to Step 16

Go to Step 12

11

Repair the open or the high resistance in the sensor low reference
circuit 252 (BR).

Did you complete the repair?

Go to Step 16

Go to Step 13

12

Inspect the ECM connector terminals for spreading or poor con-
nections.

Did you find and correct the condition?

Go to Step 16

Go to Step 13

13

Replace the faulty ECM.

Did you complete the replacement?

Go to Step 16

14

Replace the faulty MAF sensor.

Did you complete the replacement?

Go to Step 16

15

Replace the faulty fuel temperature sensor.

Did you complete the replacement?

Go to Step 16

16

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 17

17

1.

Using the Scan Tool select “Capture Info,” Review Info.” Are
any DTC’s displayed that have not been diagnosed?

Go to the appli-

cable DTC

table.

System OK.

Step

Action

Value(s)

Yes

No

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On-Board Diagnostics OBD-111

5745804

DTC P0182 Fuel Temperature Sensor Circuit Low Voltage (Figure OBD-33)

Figure OBD-33: Fuel Temperature Sensor Circuit

Circuit Description

The fuel temperature sensor is a thermistor. The engine control module (ECM) supplies the fuel temperature sensor a reference
voltage of 5 volts on the signal circuit and also provides a low reference circuit to the sensor. When the fuel temperature sensor is
cold, the resistance is high. The fuel temperature sensor signal voltage remains near the supplied voltage cold and decreases the
signal voltage as the sensor warms. The control module monitors the fuel temperature sensor signal circuit in order to calculate the
temperature of the fuel entering the engine. If the ECM detects an excessively low fuel temperature signal voltage, a high tempera-
ture indication, this DTC will set.

Conditions for Setting the DTC

The fuel temperature sensor is more than 129.75°C (265.55°F) for 2 seconds.

OR

The fuel temperature sensor voltage is less than 0.24 volts for 2 seconds.

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this informa-

tion in the Freeze Frame/Failure Records.

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