The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, contained in the fuel sender assembly, and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

Electrical Information Reference

Scan Tool Reference

Special Tools Required

1. Turn OFF the ignition.
2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
3. Disconnect the chassis fuel hose from the fuel rail. Refer to Metal Collar Quick Connect Fitting Service .
4. Install the J 37287 between the chassis fuel hose and the fuel rail.
5. Open the valve on the J 37287 .
6. Turn ON the ignition, with the engine OFF.
7. Command the fuel pump relay ON with a scan tool.
8. Bleed the air from the CH-48027 .
9. Command the fuel pump relay ON and then OFF with a scan tool.
10. Close the fuel feed pipe shut-off valve.
11. Monitor the CH-48027 for one minute.

⇒	If the fuel pressure remains constant, replace the fuel sender assembly.

⇒	If the fuel pressure does not remain constant, locate and replace the leaking fuel injectors.

Important: 

1. Turn ON the ignition, with the engine OFF.
2. Command the fuel pump relay ON with a scan tool.

⇒	If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis .

3. Turn OFF the ignition.
4. Turn OFF all accessories.
5. Install a CH-48027 . Refer to Fuel Pressure Gage Installation and Removal .
6. Turn ON the ignition, with the engine OFF.

Important: 

•	The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

•	DO NOT start the engine.

7. Command the fuel pump relay ON with a scan tool.
8. Observe the CH-48027 with the fuel pump commanded ON. The fuel pressure should be 384-425 kPa (55-61 psi).

⇒	If the fuel pressure is less than 384 kPa (55 psi), inspect for a restricted fuel feed pipe, poor connections at the harness connectors and ground circuits of the fuel pump, or a faulty fuel sender assembly.

⇒	If the fuel pressure is more than 425 kPa (61 psi), replace the fuel sender assembly.

Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.

9. Monitor the CH-48027 for 1 minute. The fuel pressure should not decrease more than 34 kPa (5 psi).

⇒	If the fuel pressure decreases more than 34 kPa (5 psi), refer to Circuit/System Testing.

10. Relieve the fuel pressure to 69 kPa (10 psi).
11. Monitor the CH-48027 for 5 minutes. The fuel pressure should not decrease more than 14 kPa (2 psi).

⇒	If the fuel pressure decreases more than 14 kPa (2 psi), replace the fuel sender assembly.

12. Remove the CH-48027 . Refer to Fuel Pressure Gage Installation and Removal .
13. Operate the vehicle within the conditions to reproduce the original symptoms.
14. Monitor the O2 and the Fuel Trim parameters with a scan tool.

⇒	If the scan tool parameters indicate a lean condition, inspect for a restricted fuel feed pipe, poor connections at the harness connectors and ground circuits of the fuel pump, or a faulty fuel sender assembly.

⇒	If the scan tool parameters do not indicate a lean condition, go to Symptoms - Engine Controls .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.