Diagnostic Instructions
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
| • | 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. |
| • | DTCs 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
Electrical Information Reference
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.
- Engine running, observe the DTC information with a scan tool. DTC P0168 should not set.
- 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
.
- 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. |
- Inspect for debris or damage to the cooling fins of the fuel cooler.
| ⇒ | If a damaged fuel cooler was found, repair or replace the cooler. |
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.
