For 1990-2009 cars
Engine Controls Components
Cell 21: Fuel Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

When the ignition switch is first turned ON, the PCM energizes the fuel pump relay which applies power to the in-tank fuel pump. The fuel pump relay will remain ON as long as the engine is running or cranking and the PCM is receiving reference pulses. If no reference pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped.

The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator controls fuel pressure by allowing excess fuel to be returned to the fuel tank.

### Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for a poor connection or damaged harness. A blown fuse may be the result, so always check for possible causes. Inspect the PCM harness and connectors for the following items:

• | Improper mating

• | Broken locks

• | Improperly formed or damaged terminals

• | Poor terminal to wire connections

• | Damaged harnesses

### Test Description

The numbers below refer to the step numbers on the Diagnostic Table:

1. Verifies that the fuel pump feed circuit is OK between the fuel pump relay and the fuel pump, and that the fuel pump can deliver adequate pressure to the fuel rail.

2. Checks the ignition feed circuit to the fuel pump relay.

3. Checks the fuel pump feed circuit for a short to battery positive voltage.

4. Checks whether the problem is being caused by an open in the fuel pump feed circuit or the fuel pump ground circuit.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain OBD System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn the ignition off.
2. Disconnect the fuel pump relay.
3. Install the fuel pump pressure gauge.
4. Connect a fused jumper between the fuel pump feed circuit at the fuel pump relay connector and battery positive voltage.
5. Note the fuel pressure gage.

Is proper fuel pressure indicated

284-325 kPa (41-47 psi)

Go to Step 3

Go to Step 8

3 |

1. Disconnect the jumper from the fuel pump relay connector.
2. Connect a test lamp between fuel pump relay Battery feed circuit and the ground circuit.
3. Turn ON the ignition, observe the test lamp.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 7

4 |

- Probe the fuel pump feed circuit with a test lamp to ground.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 6

5 |

- Check for a short to battery positive voltage in the fuel pump feed circuit.

Did you find and correct the condition?

--

Go to Step 13

--

6 |

1. Check for a poor terminal connection at the fuel pump relay. Refer to Testing for Continuity and Intermittents and Poor Connections Diagnosis .
2. If a problem is found, replace terminal(s) as necessary. Refer to Repairing Connector Terminals , Connector Repairs and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

7 | Replace the underhood wiring junction block. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | --
8 | Probe the fuel pump feed circuit at the modular fuel sender harness connector with a test lamp to chassis ground. Does the test light illuminate? | -- | Go to Step 10 | Go to Step 9
9 |

1. If the fuel pump fuse needs replacing, replace it.
2. Locate and repair open or short to ground in the fuel pump feed circuit. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10 |

1. If the fuel pump fuse needs replacing, replace it.
2. Locate and repair open in the fuel pump ground circuit. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11 | Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 |

1. If the fuel pump fuse needs replacing, replace it.
2. Replace the fuel pump. Refer to Fuel Sender Assembly Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13 |

1. Reassemble all previously disassembled parts.
2. Turn ON the ignition, with the engine off.
3. Note the fuel pressure gage.

Is proper fuel pressure indicated?

284-325 kPa (41-47 psi)

OK

Go to Step 2