Diagnostic Procedures

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.

NOTE: Before performing this procedure, place a dry chemical (class "B") fire extinguisher near work area.

Raise vehicle. Inspect fuel tank and fuel pipes for damage or external leaks. Did you find fuel leaking from fuel tank? If yes, go to step 6. If no, go to next step.
Turn ignition on, with engine off. With scan tool, command fuel pump ON. Inspect for fuel leaking from fuel pipes. Did fuel leak from fuel pipes? If yes, go to step 7. If no, go to next step.
Install Fuel Tank Cap Adapter (J-41415-40). Connect Evaporative Emissions System Tester (J-41413-200) to fuel tank cap adapter. With scan tool, seal EVAP system. DO NOT exceed 15 in. H2O. With EVAP pressure/purge diagnostic station, pressurize fuel tank. Did fuel leak from fuel tank? If yes, go to step 6. If no, go to next step.

NOTE: Fuel tank may need to be partially lowered during this step.

With EVAP pressure/purge diagnostic station, maintain pressure in fuel tank. With Ultrasonic Leak Detector (J-41416), test for leaks above fuel level in following locations:
- Fuel tank, fill limiter vent valve, pressure relief valve and rollover valves.
- Fuel sender housing and fuel sender seal.
- Fuel Tank Pressure (FTP) sensor seal.
- EVAP vapor pipes.
- Fuel fill pipe and hose.
Did you locate a fuel leak? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
Replace fuel tank. After repairs, system is okay.
Replace leaking fuel pipe. After repairs, system is okay.
Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step 2.