GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 6.6L (LLY) 🢒 DTC P0181

Circuit Description

The fuel temperature sensor is a thermistor that measures the temperature of the fuel being returned to the fuel tank. The engine control module (ECM) supplies the fuel temperature sensor a reference voltage of 5 volts on the signal circuit and a ground for the low reference circuit. When the fuel temperatures are low, the resistance is high. The signal voltage remains near the supplied voltage cold and decreases as the sensor warms. The ECM uses a fuel temperature rationality test to determine if the fuel temperature input is inaccurate. The ECM will record the amount of time the engine is OFF. During cold start the ECM will calculate the temperature difference between the fuel temperature sensor and the intake air temperature (IAT). Before failing this diagnostic, the ECM will perform a calculation to determine the presence of a block heater. If this diagnostic fails, DTC P0181 sets.

DTC Descriptor

This diagnostic supports the following DTC:

DTC P0181 Fuel Temperature Sensor Performance

Conditions for Running the DTC
    • DTCs P0112, P0113, P0182, P0183, P0500, or P2610 are not set.
    • The engine is running.
    • The engine must be OFF for 10 hours or more.
    • The start-up intake air temperature (IAT) is more than 15°C (59°F).
    • DTC P0181 runs once per drive cycle within the enabling conditions.

Conditions for Setting the DTC
    • The ECM detects the fuel temperature and the engine coolant temperature (ECT) are more than 9.75°C (18°F) of each other at start-up.
    • The IAT has decreased less than 5.25°C (10°F) after the engine has been 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 diagnostic 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 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
    • 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.

Diagnostic Aids
    • Ensure that an engine block heater or front grill blanket is not being used at temperatures above -17C ( 0°F ).
    • A engine block heater is used at temperatures above -17C ( 0°F ) this DTC may set.
    • A front grill blanket is used at temperatures above -17C ( 0°F ) this DTC may set.
    • If this DTC cannot be duplicated, the conditions may be intermittent. Refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if the IAT sensor is within the normal range. If the value is outside of the specification, the IAT sensor may be inaccurate or the circuit may have high resistance.

    2.

  2. This step determines if the fault is present at the time of diagnosis.

    3.

  3. Reprogram the replacement ECM. Refer to the latest techline information for ECM programming.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls 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

Important: The intake air temperature (IAT) sensor will start to warm-up as soon as the ignition is turned ON.

  1. Allow the engine to cool to ambient temperature by comparing IAT and engine coolant temperature (ECT) parameters.
  2. Record the ambient air temperature surrounding the vehicle using an accurate thermometer.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the IAT parameter with a scan tool.

Does the scan tool indicate a temperature close to the ambient air temperature, within the specified range?

10°C (18°F)

Go to Step 3

Go to Step 5

3
  1. Observe the Fuel Temperature Sensor parameter with a scan tool.
  2. Observe the IAT Sensor parameter with a scan tool.

Is the difference between the Fuel Temperature Sensor parameter and the IAT Sensor parameter more than the specified value?

10°C (18°F)

Go to Step 7

Go to Step 4

4

  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 5

Go to Diagnostic Aids

5
  1. Disconnect the mass air flow (MAF)/IAT sensor connector.
  2. Turn ON the ignition with the engine OFF.
  3. Measure the voltage from the IAT signal circuit at the MAF sensor harness connector to a good ground with a DMM. Refer to in Wiring Systems.

is the voltage measured within the specified range?

4.9-5.1 V

Go to Step 6

Go to Step 8

6
  1. Turn OFF the ignition.
  2. Wait approximately 60 seconds or until the engine control module (ECM) powers down.
  3. Measure the resistance from the low reference circuit of the IAT sensor harness connector to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the resistance less than the specified value?

5 ohms

Go to Step 13

Go to Step 11

7
  1. Disconnect the air filter outlet duct to access the fuel temperature sensor.
  2. Disconnect the fuel temperature sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the fuel temperature sensor signal circuit to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

is the voltage measured within the specified Range?

4.9-5.1 V

Go to Step 9

Go to Step 10

8
  1. Turn OFF the ignition.
  2. Disconnect the ECM connectors.
  3. Test the IAT signal circuit for the following conditions:
    4. • An open
    • A short to ground
    • High resistance
    • Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

9
  1. Turn OFF the ignition
  2. Wait approximately 60 seconds or until the ECM powers down.
  3. Measure the resistance from the low reference circuit of the fuel temperature sensor harness connector to a good ground with DMM. Refer to Circuit Testing in Wiring Systems

Is the resistance less than the specified value?

5 ohms

Go to Step 12

Go to Step 11

10

Repair the high resistance in the fuel temperature sensor signal circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

11

Repair the open or the high resistance in the sensor low reference circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

12

Inspect the fuel temperature sensor for any of the following conditions:

    • A fuel temperature sensor leaking fuel internally through the sensor
    • Corrosion on the fuel temperature sensor harness connector and sensor terminals
    • Intermittent and poor connections--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 18

Go to Step 17

13

Inspect the MAF/IAT sensor for any of the following conditions:

    • Corrosion on the MAF/IAT sensor harness connector and sensor terminals
    • Intermittent and poor connections--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 18

Go to Step 16

14

Test for intermittent and for poor connections at the ECM connector terminals. Repair as necessary. 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 18

Go to Step 15

15

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 18

--

16

Replace the MAF/ IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 18

--

17

Replace the fuel temperature sensor. Refer to Fuel Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 18

--

18
  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 19

19

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