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 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 semi-returnless design. The fuel pressure regulator is a part of the fuel gage sensor assembly, eliminating the need for a return pipe from the engine. A semi-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.

### Reference Information

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Engine Control Module Scan Tool Information

#### Special Tools

• | CH-48027 Digital Pressure Gage

• | J 37287 Fuel Line Shut-off Adapter

### Circuit/System Verification

1. Turn the ignition OFF.
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 the ignition ON 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 OFF with a scan tool.
10. Close the fuel feed pipe shut-off valve.
11. Monitor the CH-48027 for 1 minute.

⇒ | If the fuel pressure remains constant, replace the fuel gauge sensor assembly.

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

### Circuit/System Testing

Important:

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

• | Verify there is adequate fuel in the fuel tank before proceeding with this diagnostic.

1. Turn the ignition ON 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 the ignition OFF.
4. Turn OFF all of the accessories.
5. Install a CH-48027 . Refer to Fuel Pressure Gage Installation and Removal .
6. Turn the ignition ON 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 between 380-410 kPa (55-60 psi).

⇒ | If the fuel pressure is less than 380 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 gage sensor assembly.

⇒ | If the fuel pressure is more than 410 kPa (60 psi), replace the fuel gauge sensor assembly.

Important: The fuel pressure may vary slightly when the fuel pump stops running. 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 gage sensor 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 gage sensor assembly.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Injector and Fuel Rail Replacement

• | Primary Fuel Level Sensor Replacement