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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Battery Voltage - Relay Switch Side | 2 | 2 | -- | --
Fuel Pump Supply Voltage | 1 | 2 | 3 | --
Fuel Pump Relay Control | P0628 00 | P0629 00 | P0629 00 | --
Fuel Pump Relay Ground | -- | 2 | -- | --
Fuel Pump Ground | -- | 2 | -- | --
1. Open fuel pump fuse, cranks no start 2. The engine cranks but does not run 3. Fuel pump operates continuously, then discharged battery

### 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.

### Diagnostic Aids

The following conditions may cause the fuel pump fuse to open:

• | The fuse F29 is faulty.

• | There is an intermittent short to ground in the fuel pump supply voltage circuit of the fuel pump.

• | The fuel pump has an intermittent internal condition.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### 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

EL-43244 Relay Puller Pliers

For equivalent regional tools, refer to Special Tools.

### Circuit/System Verification

With the ignition ON, engine OFF, command the fuel pump relay ON and OFF several times using the scan tool output control function. You should either hear or feel the relay click and the fuel pump should turn ON and OFF with each command.

⇒ | If the fuel pump operates continuously, test for a faulty KR23A Fuel Pump Relay or a short to voltage in the G12 Fuel Pump supply voltage circuit of the fuel pump.

### Circuit/System Testing

1. With the ignition OFF, remove the KR23A Fuel Pump Relay from the rear electrical center using the EL-43244 Relay Puller Pliers .
2. With the ignition ON, engine OFF, probe the control circuit terminal 85 of the KR23A Fuel Pump Relay connector with a test lamp that is connected to a good ground. Command the KR23A Fuel Pump Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF with each command.

⇒ | If the test lamp does not turn ON and OFF, test for an open or a short to ground in the KR23A Fuel Pump Relay control circuit, or an intermittent or a poor connection at the K20 Engine Control Module (ECM) terminal 46 (X1). If the circuit tests normal, replace the K20 Engine Control Module (ECM).

⇒ | If the test lamp remains illuminated with each command, test for a short to voltage in the control circuit of the KR23A Fuel Pump Relay, or an intermittent or a poor connection at the K20 Engine Control Module (ECM). If the circuit tests normal, replace the K20 Engine Control Module (ECM).

3. Connect a test lamp between the control circuit of the KR23A Fuel Pump Relay and the ground circuit of the KR23A Fuel Pump Relay. Command the fuel pump relay ON and OFF with a scan tool.

⇒ | If the test lamp does not turn ON and OFF, repair the open or the high resistance in the ground circuit of the KR23A Fuel Pump Relay.

⇒ | If the test lamp does turn ON and OFF, test for an intermittent and for a poor connection at the KR23A Fuel Pump Relay, or a faulty KR23A Fuel Pump Relay.

4. Inspect the fuel pump fuse F29.

⇒ | If the fuel pump fuse F29 is open, test for a short to ground in the supply voltage circuit of the G12 Fuel Pump, or a faulty fuel sender.

5. With the ignition ON, engine OFF, probe the battery positive voltage circuit of the KR23A Fuel Pump Relay fuse F29 with a test lamp that is connected to a good ground.

⇒ | If the test lamp does not illuminate, repair the open in the fuse F29 battery positive voltage circuit.

6. Connect a 15 A fused jumper wire between the battery positive voltage circuit fuse F29 of the KR23A Fuel Pump Relay and the supply voltage circuit of the G12 Fuel Pump.

⇒ | If the fuel pump operates, test for an intermittent or poor connection at the KR23A Fuel Pump Relay, or a faulty KR23A Fuel Pump Relay.

⇒ | If the fuel pump does not operate, test for an open or high resistance in the supply voltage circuit of the G12 Fuel Pump, an open or high resistance in the ground circuit of the G12 Fuel Pump, an intermittent or poor connection at the fuel sender connector, or a faulty fuel sender.

### Component Testing

#### Static Test

1. Measure for 70-110 Ω between terminal 85 and 86 of the KR23A Fuel Pump Relay.

⇒ | If the resistance is not within the specified range, replace the KR23A Fuel Pump Relay.

2. Measure for infinite resistance between the following terminals of the KR23A Fuel Pump Relay:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If continuity is detected, replace the KR23A Fuel Pump Relay.

3. Connect a 20 A fused jumper wire from the positive terminal of the battery to KR23A Fuel Pump Relay terminal 85. Connect a jumper wire from the negative terminal of the battery to KR23A Fuel Pump Relay terminal 86. Measure for less than 2 Ω between fuel pump relay terminal 30 and 87.

⇒ | If the resistance measures more than 2 Ω, replace the KR23A Fuel Pump Relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | NEED LINK (Fuel Tank Fuel Pump Module Replacement).

• | Relay Replacement

• | Control Module References for ECM replacement, setup, and programming