GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 6.6L (LLY) 🢒 DTC P0168

Circuit Description

The fuel temperature sensor is a thermistor type sensor. The engine control module (ECM) supplies 5 volts and a ground circuit to the sensor. When the ECM detects a fuel temperature sensor above a pre-determined value, a type C code, no malfunction indicator lamp (MIL) sets. A fuel cooler located in front of the fuel tank is used to help keep the fuel temperature at an acceptable limit.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0168 Engine Fuel Over-Temperature

Conditions for Running the DTC
    • The ignition is ON.
    • DTC P0168 runs continuously within the enabling conditions.

Conditions for Setting the DTC

The fuel temperature sensor is above 122°C (252°F) for more than 5 seconds.

Action Taken When the DTC Sets
    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC
    • 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 non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Test Description

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

  1. This step inspects for a condition in the fuel cooler that could cause the fuel temperature sensor to increase above the pre-determined specification due to a lack of cooler efficiency.

    2.

  2. This step tests for a voltage above or below the 5 volts supplied by the ECM.

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 - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Inspect the fuel cooler located in front of the fuel tank for debris restricting the airflow or damage to the cooling fins.
  2. Inspect the fuel lines for kinks or damage.
  3. Clean or replace the above listed components as necessary.

Did any of the components require a repair?

--

Go to Step 11

Go to Step 3

3
  1. Disconnect the air filter outlet duct to access the fuel temperature sensor.
  2. Disconnect the fuel temperature sensor electrical connector.
  3. Turn ON the ignition.
  4. Probe the fuel temperature sensor signal circuit with a DMM connected to ground.

Is the voltage near the specified value?

5 V

Go to Step 4

Go to Step 5

4
  1. Connect a test lamp to B+.
  2. Probe the low reference circuit of the fuel temperature sensor connector.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 6

5

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) connector that contains the fuel temperature sensor signal circuit.
  3. Inspect the signal circuit for an open or short to voltage or ground and repair the circuit as necessary.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

6
  1. Turn OFF the ignition.
  2. Disconnect the ECM connector that contains the fuel temperature sensor low reference circuit.
  3. Inspect the fuel temperature sensor low reference circuit and connectors for an open or high resistance and repair the circuit as necessary.

Did you complete the repair?

--

Go to Step 11

--

7

Inspect for poor connections at the fuel temperature sensor and 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 11

Go to Step 9

8

Inspect for poor connections at the ECM and 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 11

Go to Step 10

9

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

Did you complete the replacement?

--

Go to Step 11

--

10

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 11

--

11
  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 12

12

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK