GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Fuel Tank Leak Test

Description

The fuel tank leak test is used to locate any fuel or fuel vapor escaping the fuel tank area. Fuel vapors escaping above the fuel level will be detected when the evaporative emission (EVAP) diagnostics complete one test cycle. The malfunction indicator lamp (MIL) will illuminate after the EVAP diagnostics have failed two test cycles.

Diagnostic Aids
    • Operate the vehicle under the condition of the customers concern. Under high temperature conditions fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
    • Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.
    • If the fuel level is low, a leak may not be evident.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for fuel leaks below the fuel tank fuel level.

    2.

  2. This step tests for fuel vapors escaping above the fuel level in the fuel tank .

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check - Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Caution: Gasoline or gasoline vapors are highly flammable. A fire could occur if an ignition source is present. Never drain or store gasoline or diesel fuel in an open container, due to the possibility of fire or explosion. Have a dry chemical (Class B) fire extinguisher nearby.

  1. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Inspect the fuel tank and fuel pipes for damage or external leaks.

Did you find fuel leaking from the fuel tank?

Go to Step 6

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump relay ON with a scan tool.
  3. Inspect for fuel leaking from the fuel pipes.

Did fuel leak from the fuel pipes?

Go to Step 7

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Install the J 41413-200 Evaporative Emissions System Tester (EEST) and the J 41415-40 Fuel Tank Cap Adaptor or the GE-41415-50 Interrupted Thread Fuel Tank Cap Adapter.

    3. Important: If the floating indicator registers any flow after stabilizing, a leak is evident.

  3. Test for a fuel tank leak referring to the J 41413-210 Operation Manual.
  4. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  5. Inspect for a fuel leak while the system is under pressure.

Did fuel leak from the fuel tank?

Go to Step 6

Go to Step 5

5

  1. Using the J 41413-200 and the J 41413-210 Operation Manual, introduce smoke into the evaporative emission (EVAP) system.

    2. Important: It may be necessary to partially lower the fuel tank. Refer to Fuel Tank Replacement .

  2. Inspect for leaks in any of the following locations:
    3. • The fuel tank, fill limiter vent valve, the pressure relief valve, and the grade vent valves--Refer to Fuel Tank Replacement .
    • The fuel sender housing and the fuel sender seal--Refer to Fuel Sender Assembly Replacement .
    • The fuel tank pressure (FTP) sensor seal--Refer to Fuel Tank Pressure Sensor Replacement .
    • The fuel fill pipe and hose--Refer to Filler Tube Replacement .
    • If equipped with a rear tank, the fuel tank, the fill limiter vent valve, the pressure relief valve, and the rollover valves--Refer to Fuel Tank Replacement .
    • If equipped with a rear tank, the fuel sender housing and the fuel sender seal--Refer to Fuel Sender Assembly Replacement .

Did you find and correct the condition?

Go to Step 8

Go to Diagnostic Aids

6

Replace the fuel tank. Refer to Fuel Tank Replacement .

Did you complete the repair?

Go to Step 8

--

7

Replace the leaking fuel pipe. Refer to Fuel Hose/Pipes Assembly Replacement .

Did you complete the replacement?

Go to Step 8

--

8

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2