Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 152 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)FUEL SYSTEMSFUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS (3.0L)TEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic
Test Description
1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to the step numbers on the diagnostic procedures.
- 2 - Command both the ON and OFF states. Repeat the commands as necessary. This can be determined by listening for an audible hiss from the fuel pump when the fuel pump relay is commanded ON or a vibration in the fuel feed line.
- 3 - This step determines if the condition is located on the coil side or the switch side of the relay.
- 5 - This step determines if the fuel pump relay is stuck closed.
- 7 - This step tests for a grounded voltage supply circuit. The fuel pump fuse supplies power to fuel pump. Disconnecting the fuel pump in-line harness connector isolates the fuel pump voltage supply circuit.
- 9 - This step verifies that the ECM is providing voltage to the fuel pump relay.
- 10 - This step verifies that the fuel pump fuse is providing voltage to the fuel pump relay.
- 11 - This step tests for an open circuit or a short to ground causing an open MaxiFuse(R).
- 12 - This step bypasses the fuel pump relay in order to activate the fuel pump.
- 13 - This step tests for an open in the fuel pump feed circuit between the in-line connector and the fuel pump relay.
- 16 - This step tests for an open or high resistance in the fuel pump ground circuit.
- 18 - This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and fuel pump for an intermittent condition.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.