2012 BMW 740Li Fuel Tank Replacement Cost

The fuel tank is filled with fuel through the fill spout. The fill spout connects to the fuel tank filler neck, which will be equipped with a check valve or release valve, to allow the fuel going into the tank to replace air inside the tank. When the tank is full, and no air remains, the pressure signals the fuel station pump to stop sending fuel. Once fuel is inside the tank, it will adjust the mechanical float that reads fuel level, and be sucked from the tank on demand by the fuel pump.

The check engine light will illuminate any time there is a failed EVAP system test. This will be indicated by the various on-board diagnostics trouble codes that are stored in the vehicle's memory. Also, in some models, there may be a popping sound accompanying the check engine light, as the leak detection pump continuously attempts to pressurize the fuel tank. A fuel tank leak may also cause difficulty starting the engine, a rough idle, and poor fuel mileage. When a fuel tank is simply corroded to the point of failure, the exterior tank condition rarely shows damage. The inside of the fuel tank will be rusted or corroded, and rust flakes or other debris may be floating in the fuel.

A vehicle with a bad fuel tank should not be driven. The corrosion, debris, and rust inside the fuel tank will be further flushed into the fuel delivery system. The vehicle should not be started until the fuel is filtered, and the fuel tank and filter are replaced. Get this fixed by a RepairPal Certified Shop

Fuel tanks failure rates vary with the age of the vehicle and environmental differences. Environments with extreme temperature fluctuation, humidity, sand, salt, or deep water will all impact the probability of a metal gas tank corroding. Most modern vehicles have plastic tanks which are impervious to corrosion. However, many have integrated emissions components (vent and return lines) that can fail and necessitate replacement of the entire tank.

When the EVAP system is checked, the purge valve and vent valve are closed, and the pressure is monitored by the fuel tank pressure sensor. If that pressure drops with both valves closed, there is a leak in the EVAP system. If pressure holds properly, the system passes, and will continue to prevent vapor emissions. The sensor is also used in testing vent valve and purge valve operation. When the valves are open, the pressure sensor reads the fuel tank pressure, and must sense a drop in pressure. If not, the purge valve or vent valve may be faulty.

When the identified component is faulty, the technician will remove all electrical and vacuum connectors, clean the mating surface for the faulty part, and install a new part. The evap system will then be allowed to run self-diagnostics to test the repair. If additional leaks are present, or other components have failed, the test will fail, and the process will restart. To help prevent issues with the EVAP system, especially the charcoal canister, avoid overfilling or topping off the fuel tank.

To help prevent issues with the EVAP system, especially the charcoal canister, avoid overfilling or topping off the fuel tank. When the tank is topped off, the charcoal canister may fill with fuel, causing degradation of the charcoal canister and system failure.

When working with fuel, the battery should always be disconnected, and proper precautions taken against fire hazards. It is recommended to replace the fuel tank retaining straps if they are corroded or damaged.

Fuel tanks are large, cumbersome, and can be extremely heavy. If the fuel tank must be replaced, a DIYer can handle the repair, but an assistant should be used to prevent injury or damage to the vehicle. The fuel tank combines electricity and fuel, and proper working knowledge of these components, and safety procedures is a must. If you feel that you are unqualified for this task, leave it to a professional technician.