GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1996 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L 🢒 Fuel Pump Electrical Circuit Diagnosis

Refer to

Fuel Pump System


Object Number: 28321 Size: FS
Fuel Injectors
Ignition Control and the Knock Sensor System
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. With the engine stopped, the fuel pump can be turned ON by using a fused jumper to apply B+ to the fuel pump test lead in the engine compartment.

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. 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

Number(s) below refer to the Step number(s) on the Diagnostic Chart:

  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.

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

    3.

  3. Checks the fuel pump relay driver circuit and the PCM are capable of controlling the fuel pump relay.

    4.

  4. Checks the fuel pump driver circuit for a short to ground.

    5.

  5. Checks the fuel pump driver circuit for an open.

    6.

  6. If the fuel pump is operating but incorrect pressure is noted, the fuel pump wiring is OK and Fuel System Pressure Test should be used for diagnosis.

    7.

  7. Checks the fuel pump feed circuit between the fuel pump relay and the fuel pump. Also checks the fuel pump ground circuit.

    8.

  8. 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 On-Board Diagnostic System Check performed?

--

Go to Step 2

Go to Powertrain OBD System Check

2
  1. Ignition OFF.
  2. Disconnect the fuel pump relay.
  3. Connect a fused jumper between the fuel pump feed circuit at the fuel pump relay connector and B+.
  4. Note the fuel pressure gage.

Is proper fuel pressure indicated?

41-47 psi

Go to Step 3

Go to Step 10

3
  1. Disconnect the jumper from the fuel pump relay connector.
  2. Connect a test light between fuel pump relay connector cavities for the ignition feed circuit and the ground circuit.
  3. Ignition ON, observe the test light.

Is the test light ON?

--

Go to Step 4

Go to Step 9

4
  1. Ignition OFF.
  2. Connect a test light between fuel pump relay connector cavities for the fuel pump relay driver circuit and the ground circuit.
  3. Observe the test light while turning ON the ignition.

Did the test light turn ON for approximately 2 seconds?

--

Go to Step 8

Go to Step 5

5
  1. Ignition OFF.
  2. Disconnect the PCM.
  3. Probe the fuel pump relay driver circuit at the PCM connector with a test light to B+.

Is the test light ON?

--

Go to Step 15

Go to Step 6

6
  1. Check for continuity in the fuel pump relay driver circuit between the PCM and the fuel pump relay.
  2. If the fuel pump relay driver circuit is open, repair it as necessary. Refer to Engine Electrical.

Was the fuel pump relay driver circuit open?

--

Go to Powertrain OBD System Check

Go to Step 7

7
  1. Check the fuel pump relay driver circuit for a poor terminal connection at the PCM.
  2. If a problem is found, replace terminal as necessary (refer to Engine Electrical).

Was a problem found?

--

Go to Powertrain OBD System Check

Go to Step 20

8
  1. Check for a poor terminal connection at the fuel pump relay.
  2. If a problem is found, replace terminal(s) as necessary. Refer to Engine Electrical.

Was a problem found?

--

Go to Powertrain OBD System Check

Go to Step 18

9

Probe the ignition feed circuit at the fuel pump relay connector with a test light to ground.

Is the test light ON?

--

Go to Step 17

Go to Step 16

10

Remove the fuel filler cap and listen for the fuel pump running.

Is the fuel pump running?

--

Go to Fuel System Pressure Test

Go to Step 11

11
  1. Raise the vehicle (leave the fuel pump feed circuit jumped to B+).
  2. Disconnect the modular fuel sender electrical connector at the fuel tank.
  3. Connect a test light between the fuel pump feed circuit and the fuel pump ground circuit at the modular fuel sender harness connector.

Is the test light on?

--

Go to Step 19

Go to Step 12

12

Probe the fuel pump feed circuit at the modular fuel sender harness connector with a test light to chassis ground.

Is the test light on?

--

Go to Step 14

Go to Step 13

13

Locate and repair open in the fuel pump feed circuit. Refer to Engine Electrical .

Is action complete?

--

Go to Powertrain OBD System Check

--

14

Locate and repair open in the fuel pump ground circuit. Refer to Engine Electrical .

Is action complete?

--

Go to Powertrain OBD System Check

--

15

Locate and repair short to ground in the fuel pump relay driver circuit. Refer to Engine Electrical.

Is action complete?

--

Go to Powertrain OBD System Check

--

16

Locate and repair open in ignition feed to the fuel pump relay. Refer to Engine Electrical.

Is action complete?

--

Go to Powertrain OBD System Check

--

17

Locate and repair open in ground circuit to the fuel pump relay. Refer to Engine Electrical.

Is action complete?

--

Go to Powertrain OBD System Check

--

18

Replace the fuel pump relay.

Is action complete?

--

Go to Powertrain OBD System Check

--

19

Replace the fuel pump.

Is action complete?

--

Go to Powertrain OBD System Check

--

20

Replace the PCM.

Important: Replacement PCM must be programmed. Refer to PCM Replacement/Programming.

Is action complete?

--

Go to Powertrain OBD System Check

--