Fuel Tank Leak Test

Fuel Tank Leak Test

The diagnosis of fuel odor may be a condition of a leaking fuel tank, filler neck or filler cap. A defective filler cap, a plugged or pinched vent pipe can cause a collapsed fuel tank. Loose mounting straps or foreign material in tank may be the cause of a rattle at the fuel tank.

Leak Check Procedure

Warning

Place a dry chemical (Class B) fire extinguisher near the area before performing a Fuel Tank Leak Check. Before removing the fuel tank for a suspected leak, make sure that the fuel pipes or the tubes are not leaking onto the tank. Once removed, make sure that the fuel is not leaking around the fuel sender O-ring. Failure to follow these precautions may result in personal injury.

This check requires the fuel sender and the O-ring to be installed.

Warning

Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

For Vehicles equipped with OnStar(R) (UE1) with Back Up Battery:

The Back Up Battery is a redundant power supply to allow limited OnStar(R) functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar(R)module). Do not disconnect the main vehicle battery or remove the OnStar(R) fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar(R) module in any way while the ignition is On or with RAP activated may cause activation of the OnStar(R) Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.

1. Disconnect the battery cables.
2. Drain the fuel tank. Refer to Fuel Tank Draining (Procedures).
3. Remove the fuel tank. Refer to Fuel Tank Replacement (Pickup) (Removal and Replacement)Fuel Tank Replacement (Cab/Chassis - Front) (Removal and Replacement)Fuel Tank Replacement (Cab/Chassis - Rear) (Removal and Replacement).
4. Cap the fuel feed tube and the fuel return tube on the fuel sender.
5. Connect a piece of hose to the filler tube nipple and plug the opposite end.
6. Submerge the tank in water or apply a soap solution to the outside of the tank.
7. Apply 35 kPa (5 psi) of air pressure to the vent hose of the fuel tank. A leak will show up as bubbles.