BMW 840i xDrive Fuel Pressure Sensor Replacement Cost

When fuel is cold, it is dense and burns slowly. If it is warm, it is less dense and burns quickly. A fuel temperature sensor in a vehicle allows the Engine Control Module to constantly monitor the temperature of the fuel and adjust how much fuel is injected into the engine. The fuel temperature sensor is usually mounted on the fuel pump inside the fuel tank. A vehicle with a diesel engine may have a fuel temperature sensor located inside the injector pump or a fuel filter housing.

The fuel temperature sensor is a type of electric resistor (called a thermistor) that is sensitive to heat. Changes in the temperature around the sensor cause changes in its electrical resistance. This difference is calculated by the Engine Control Module and the information is used to adjust the air to fuel mixture ratio in differing temperature conditions.

The most likely symptom of a faulty fuel temperature sensor is a check engine light. When the sensor goes bad, the Engine Control Module signals the driver that there is a problem by turning on the dash light. Poor fuel economy might also be noticed. In some cases, a failing fuel temperature sensor could lead to hard starting of the engine or an engine misfire and poor performance.

The most likely effect of a bad fuel temperature sensor is poor fuel economy. The engine will work to compensate for the faulty sensor, but fuel will be wasted. Under some conditions, a vehicle may have trouble starting, may run poorly, or may stall if the fuel temperature sensor is not working properly. A diagnostic test at a repair shop should be run any time a check engine light comes on.

There is no scheduled maintenance or replacement interval for a fuel temperature sensor. Although these sensors do sometimes go bad, they are supposed to last the lifetime of the vehicle.

A technician will begin diagnosis of a faulty fuel temperature sensor by running a diagnostic scan with a scan tool connected to the vehicle's data port. The scan will not tell the technician if the sensor is bad, but it can reveal if the circuit for the sensor has a fault in it. If the scan is positive, the technician will access the sensor, unplug the harness wires, and test the sensor as well as the wire harness plugs. Using a multimeter, the technician will check the resistance reading of the temperature sensor. If the readings are off, the sensor needs to be replaced. If the readings are normal, the harness is checked for continuity with the multimeter.

To replace the fuel temperature sensor in most vehicles, a technician must remove the fuel pump assembly from the fuel tank. First, the technician will relieve the residual pressure in the fuel system by disabling the fuel pump (usually by removing a fuse) and cranking the ignition. Then the battery is disconnected. On some cars and SUVs, the top of the fuel tank and the fuel pump assembly are accessible from inside the passenger compartment. If this is the case, the technician removes the back seat and an access cover in the floor below. On trucks, and on many cars, the fuel tank must be removed from underneath the vehicle in order to gain access to the fuel pump assembly. In either case, once access to the fuel pump assembly is achieved, the technician will unplug the wiring harness connectors from the top of the assembly. The fuel lines are detached, often using a special tool for the connectors. The technician will remove the retaining ring that holds the fuel pump assembly in place and pull the assembly out of the tank. The fuel temperature sensor is unplugged from the assembly and detached. A new sensor is installed in its place. The pump is inserted into the tank, secured, and plugged in. If the fuel tank was removed from the vehicle, it is reinstalled. The fuel system is enabled and the system is tested.

RepairPal recommends installing a new fuel pump assembly gasket when a fuel temperature sensor is being replaced. Also, any mounting hardware for the fuel tank that might be compromised should also be replaced.

The electrical system on the vehicle should be disabled to prevent accidental arcing of wires during the repair that might cause the open fuel system to ignite.

If the fuel pump assembly is easily accessible underneath the rear seat of a vehicle, someone with intermediate to advanced DIY skills might be able to tackle the job. A diagnostic scan is necessary and experience with a multimeter is needed to avoid replacing a sensor that is not bad. If the fuel tank needs to be removed from the vehicle, the repair should be left to a qualified technician at a trusted repair shop.