GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Denali 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC P0168

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0168: Engine Fuel Over-Temperature

Circuit/System Description

Fuel is drawn from the fuel tank through the fuel heater, then to the fuel injection pump. Fuel temperature is monitored by the fuel temperature sensor, which is located in the fuel return line on the engine. The engine control module (ECM) supplies 5 volts and a ground circuit to the sensor. A fuel cooler located in front of the fuel tank is used to help keep the fuel temperature at an acceptable limit. When the ECM detects a fuel temperature above the pre-determined value, this diagnostic will fail, but will not turn the malfunction indicator lamp (MIL) ON.

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.
    • DTC P0181, P0182 or P0183 are not set.

Action Taken When the DTC Sets

DTC P0168 is a Type C DTC.

Conditions for Clearing the DTC

DTC P0168 is a Type C DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Output Controls
    •  Scan Tool Data Definitions

Circuit/System Verification
  1. The Fuel Temperature and ECT Temperature parameters should closely match each other when the engine has not been started and soaked overnight.
  2. Engine running, observe the DTC information with a scan tool. DTC P0168 should not set.
  3. 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 data.

Circuit/System Testing

Important: Fuel temperature overheating may be cause by a fuel heater element that is stuck on. Refer to Fuel Heater Always On .

  1. With ignition ON and the engine OFF, observe the Fuel Temperature and ECT Temperature parameters with a scan tool.
    2. ⇒If the temperatures do not closely match each other when the engine has cold soaked overnight, test for a skewed fuel temperature sensor. Refer to Component Testing in the diagnostic.
  2. Inspect for debris or damage to the cooling fins of the fuel cooler.
    3. ⇒If a damaged fuel cooler was found, repair or replace the cooler.

Component Testing

  1. Remove the fuel temperature sensor from the engine.
  2. Measure the resistance of the sensor at different ambient temperatures and record results. Compare the results to the Temperatures vs. Resistance Fuel Temperature table. Refer to Temperature Versus Resistance .
    3. ⇒If the fuel temperature sensor is skewed, replace the sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Fuel Temperature Sensor Replacement
    •  Fuel Cooler Replacement