DTC P0168. GMC Truck TopKick C-Series (Conventional) C4/C5 2007

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2007 🢒 TopKick C-Series (Conventional) C4/C5 🢒 DTC 🢒 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

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. 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

•	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.

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

Circuit/System Verification

The Fuel Temperature and ECT Temperature parameters should closely match each other when the engine has not been started and soaked overnight.

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 .

With ignition ON and the engine OFF, observe the Fuel Temperature and ECT Temperature parameters with a scan tool.

⇒	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.

Component Testing

Remove the fuel temperature sensor from the engine.
Measure the resistance of the sensor at different ambient temperatures and record results. Compare the results to the Temperatures vs. Resistance table .

⇒	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