For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit/System Description

The engine control module (ECM) enables the fuel pump relay when the ignition switch is turned ON. The ECM will disable the fuel pump relay within 2 s unless the ECM detects ignition reference pulses. The ECM continues to enable the fuel pump relay as long as ignition reference pulses are detected. The ECM disables the fuel pump relay within 2 s 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 is attached 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 at 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.

### Reference Information

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

#### Special Tools

CH-48027 Digital Pressure Gage

J 43936 Fuel Pressure Adapter Cap

J 43937 Fuel Pressure Adapter Lines

SA9127E-7 Fuel Pressure/Flow Adapter

For equivalent regional tools, refer to Special Tools.

### Circuit/System Verification

Note:

• | Inspect the fuel system for damage or external leaks before proceeding.

• | Verify that an adequate amount of fuel is in the fuel tank before proceeding.

• | The KR23A Fuel Pump Relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

• | Before proceeding with this test review the CH 48027[dash ]5 User Manual for safety information and instructions.

1. Ignition ON, engine OFF, command the KR23A Fuel Pump Relay ON with a scan tool. You should hear the G12 Fuel Pump turn ON and OFF.

⇒ | If the G12 Fuel Pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis.

2. Ignition OFF, all accessories OFF, install a CH-48027 Digital Pressure Gage . Refer to Fuel Pressure Gage Installation and Removal.
3. Ignition ON, engine OFF, command the KR23A Fuel Pump Relay ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 PSI) and does not decrease more than 34 kPa (5 PSI) in 5 min.

### Circuit/System Testing

Note:

• | The KR23A 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.

1. Ignition ON, engine OFF, command the KR23A Fuel Pump Relay ON with a scan tool and observe the fuel pressure gauge while the G12 Fuel Pump is operating. Verify the fuel pressure is between 345-414 kPa (50-60 PSI).

⇒ | If the fuel pressure is greater than the specified range, replace the G12 Fuel Pump.

⇒ | If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the G12 Fuel Pump.

• | Restricted fuel feed pipe

• | Restricted or clogged strainer

• | Inspect the G12 Fuel Pump harness connectors and the ground circuits of the G12 Fuel Pump for poor connections.

2. Verify that the fuel pressure does not decrease more than 34 kPa (5 PSI) in 5 min.

⇒ | If the fuel pressure decreases more than the specified value, perform the following procedure:

2.1. | Ignition OFF, relieve fuel pressure.

2.2. | Disconnect the front fuel pump fuel feed hose from the fuel rail.

2.3. | Connect the front fuel pump fuel feed hose to the inlet side of SA9127E-7 Fuel Pressure/Flow Adapter using the J 43937 Fuel Pressure Adapter Lines .

2.4. | Connect the fuel rail to the ON/OFF valve side of the SA9127E-7 Fuel Pressure/Flow Adapter using the J 43937 Fuel Pressure Adapter Lines .

2.5. | Cap the pressure test port on the SA9127E-7 Fuel Pressure/Flow Adapter with the J 43936 Fuel Pressure Adapter Cap .

2.6. | Open the valve on the SA9127E-7 Fuel Pressure/Flow Adapter .

2.7. | Ignition ON, command the KR23A Fuel Pump Relay ON with a scan tool and bleed the air from the CH-48027 Digital Pressure Gage .

2.8. | Command the KR23A Fuel Pump Relay ON for a minimum of 10 s with a scan tool.

2.9. | Close the valve on the SA9127E-7 Fuel Pressure/Flow Adapter .

2.10. | Monitor the fuel pressure for 1 min.

⇒ | If the fuel pressure decreases more than 34 kPa (5 PSI) within the specified time, locate and replace the leaking fuel injector(s).

⇒ | If the fuel pressure does not decrease more than 34 kPa (5 PSI) within the specified time, replace the G12 Fuel Pump.

3. Relieve the fuel pressure to 69 kPa (10 PSI). Verify that the fuel pressure does not decrease more than 14 kPa (2 PSI) in 5 min.

⇒ | If the fuel pressure decreases more than the specified value, replace the G12 Fuel Pump module.

4. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 Digital Pressure Gage . The fuel pressure should not drop off during acceleration, cruise or hard cornering.

⇒ | If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the G12 Fuel Pump.

• | Restricted fuel feed pipe

• | Restricted or clogged strainer

• | Inspect the harness connectors and the ground circuits of the G12 Fuel Pump for poor connections

5. If the fuel system tests normal, refer to Symptoms - Engine Controls.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Injector Fuel Feed Pipe Replacement

• | Fuel Injector Replacement

• | Fuel Pump Fuel Feed Hose Replacement - Front

• | Fuel Pump Fuel Feed Hose Replacement - Rear

• | Fuel Tank Fuel Pump Module Replacement