For 1990-2009 cars

## Fuel Pump Electrical Circuit Diagnosis w/LY7

### 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) provides ignition voltage to the coil side of the fuel pump relay whenever the engine is cranking or running. The control module enables the fuel pump relay as long as the engine is cranking or running, and ignition system reference pulses are received. If no ignition system reference pulses are received, the control module turns OFF the fuel pump. The fuel pump relay control circuit is equipped with a feedback circuit that is pulled up to 2.5 volts within the ECM. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

### Diagnostic Aids

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

• | The fuse is faulty.

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

• | The fuel pump has an intermittent internal condition.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Description and Operation

Fuel System Description

#### 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

J 43244 Relay Puller Pliers

### Circuit/System Verification

Note: Fuel pump DTCs may set when using the Fuel Pump output control.

1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump operate for 2-3 seconds and then turn OFF.
2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

### Circuit/System Testing

1. Ignition OFF, the fuel pump should not be operating.

⇒ | If the fuel pump operates continuously, test for a short to voltage in supply voltage circuit of the fuel pump. If the circuit/connections test normal, replace the fuel pump relay.

2. Test the fuel pump fuse. The fuse should not be open.

⇒ | If the fuel pump fuse is open, test for a short to ground in the supply voltage circuit of the fuel pump. If the circuit/connections test normal, replace the fuel pump.

3. Ignition OFF, remove the fuel pump relay from the electrical center.
4. Ignition ON, test for battery voltage between the B+ voltage circuit of the fuel pump relay and ground.

⇒ | If less than B+, repair the B+ voltage circuit of the fuel pump relay for an open/high resistance.

5. Connect a 15 A fused jumper wire between the B+ circuit of the fuel pump relay and the supply voltage circuit of the fuel pump. The fuel pump should operate.

⇒ | If the fuel pump does not operate, test for the following conditions:

• | An open/high resistance in the supply voltage circuit of the fuel pump

• | An open/high resistance in the ground circuit of the fuel pump

⇒ | If the above circuit/connections test normal, replace the fuel pump.

6. If all circuit/connections test normal, test or replace the fuel pump relay.

### Component Testing

1. Measure for 135-185 Ω between terminals 85 and 86 of the fuel pump relay.

⇒ | If the resistance is not within the specified range, replace the fuel pump relay.

2. Measure the resistance between the terminals of the fuel pump relay listed below. The DMM should display O.L.

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If less than the specified value, replace the fuel pump relay.

3. Connect a 15 A fused jumper wire from the positive terminal of the battery to relay terminal 85. Connect a jumper wire from the negative terminal of the battery to relay terminal 86. Test for less than 2 Ω between terminals 30 and 87 of the relay.

⇒ | If greater than the specified range, replace the fuel pump relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Primary Fuel Tank Module Replacement

• | Relay Replacement