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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Engine 🢒 Engine Electrical 🢒 Fuel Pump Electrical Circuit Diagnosis

Object Number: 372984 Size: MF
Engine Controls Component Views
Fuel System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

When the ignition switch is ON, the PCM activates the in-tank fuel pump. The fuel pump remains ON as long as the PCM receives reference pulses from the ignition system. If there are no reference pulses, the PCM turns the fuel pump OFF after about 2-3 seconds. The pump delivers fuel to the fuel rail and injectors. The fuel pressure regulator, located in the fuel tank, maintains the system pressure at 380-410 kPa (55-60 psi). Excess fuel returns to the fuel tank. When the engine is stopped, a scan tool in the output controls function can turn ON the fuel pump.

Improper fuel system pressure results in one or many of the following symptoms:

    • Cranks but will not run
    • Cuts out, may feel like an ignition problem
    • Poor fuel economy
    • Loss of power
    • Hesitation
    • DTCs

Diagnostic Aids
    • The following may cause an intermittent:
       - Poor connections; Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
       - Corrosion
       - Mis-routed harness.
       - Rubbed through wire insulation.
       - Broken wire inside the insulation.
    • The following conditions may have caused the fuel pump fuse to open:
       - The fuse was faulty
       - There is an intermittent short in the fuel pump power feed circuit.
       - The fuel pump has an intermittent internal problem.
    • For an intermittent, refer to Symptoms .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Refer to the thumbnail wiring schematic for the proper terminal identification.

    2.

  2. The test lamp only illuminates for two seconds even though the scan tool commanded position is ON. You will have to command the fuel pump OFF then ON to re-enable the PCM fuel pump control.

    3.

  3. Inspect the fuel pump fuse for an open. If the fuse is open, test the circuit for a short to ground.

    4.

  4. Inspect the fuel pump fuse for an open. If the fuse is open, test the circuit for a short to ground.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Inspect the fuel pump fuse for being open.

Is the fuse open?

--

Go to Step 9

Go to Step 3

3

Important: For terminal identification, refer to Electrical Center Identification Views in Wiring Systems.

  1. Install a scan tool.
  2. Disconnect the fuel pump relay from the underhood electrical center 2.
  3. Turn ON the ignition leaving the engine OFF.
  4. Probe the fuel pump relay battery feed circuit at the underhood electrical center with the test lamp J 35616-200 connected to battery ground.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 12

4

Probe the fuel pump relay ground circuit at the underhood electrical center 2 with the test lamp J 35616-200 connected to B+.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 13

5

  1. Probe the fuel pump relay control circuit at the underhood electrical center 2 with the test lamp J 35616-200 connected to ground.
  2. Enable the fuel pump using the scan tool.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 11

6

Important: Ignition must be ON before performing this step.

Jumper the fuel pump relay battery feed circuit to the fuel pump relay load circuit at the underhood electrical center 2 using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.

Does the fuel pump operate?

--

Go to Step 18

Go to Step 7

7
  1. Leave the fused jumper wire connected.
  2. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  3. Disconnect the fuel pump harness connector at the Body Pass Through connector. Refer to

    Outside Left of Rear Floor Pan, Forward of Rear Axle
    Object Number: 383738 Size: MF
    (1)C405B
    (2)I/P wiring harness
    (3)C405C
    (4)Rear wheel speed sensor harness
    in Wiring Systems.
  4. Probe the fuel pump power feed circuit at the Body Pass Through connector with the test lamp J 35616-200 connected to ground.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 14

8
  1. Leave the fused jumper wire connected.
  2. Connect the test lamp J 35616-200 between the battery feed circuit and the ground circuit at the Body Pass Through connector. Refer to

    Outside Left of Rear Floor Pan, Forward of Rear Axle
    Object Number: 383738 Size: MF
    (1)C405B
    (2)I/P wiring harness
    (3)C405C
    (4)Rear wheel speed sensor harness
    in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 25

Go to Step 15

9
  1. Turn OFF the ignition.
  2. Remove the fuel pump relay.
  3. Remove the fuel pump fuse.
  4. Turn On the ignition leaving the engine OFF.
  5. Probe the battery feed circuit for the fuel pump relay at the underhood electrical center 2 with the test lamp J 35616-200 connected to B+.

Does the test lamp illuminate?

--

Go to Step 20

Go to Step 10

10
  1. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Disconnect the fuel pump harness connector at the Body Pass Through connector. Refer to

    Outside Left of Rear Floor Pan, Forward of Rear Axle
    Object Number: 383738 Size: MF
    (1)C405B
    (2)I/P wiring harness
    (3)C405C
    (4)Rear wheel speed sensor harness
    in Wiring Systems.
  3. Probe the load circuit for the fuel pump relay at the underhood electrical center 2 with the test lamp J 35616-200 connected to B+.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 21

11
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the opposite side of the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
  3. Test the fuel pump relay control circuit for the following conditions.
    4. • An open
    • A short to ground
    • A short to voltage

Did you find any of the above conditions?

--

Go to Step 17

Go to Step 22

12
  1. Repair the open or grounded battery feed circuit to the relay. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the fuel pump fuse if the fuse is open.

Is the action complete?

--

Go to Step 29

--

13

Repair the open relay ground circuit. Refer to Wiring Repairs in Wiring Systems .

Is the action complete?

--

Go to Step 29

--

14

Repair the open circuit between the underhood electrical center 2 and the Body Pass Through connector. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 29

--

15

Repair the open fuel pump ground circuit. Refer to Wiring Repairs in Wiring Systems .

Is the action complete?

--

Go to Step 29

--

16

Repair the short to ground in the fuel pump relay load circuit between the relay and the Body Pass Through connector. Refer to Wiring Repairs in Wiring Systems .

Is the action complete?

--

Go to Step 29

--

17

Repair the fuel pump relay control circuit. Refer to Wiring Repairs in Wiring Systems .

Is the action complete?

--

Go to Step 29

--

18
  1. Inspect for poor connections at the relay (underhood electrical center). Refer to Wiring Repairs in Wiring Systems.
  2. If you find a poor connection repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 29

Go to Step 19

19

Replace the relay.

Is the action complete?

--

Go to Step 29

--

20

  1. Repair the short to ground in the fuel pump relay battery feed circuit between the relay and the fuse. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the open fuse.

Is the action complete?

--

Go to Step 29

--

21
  1. Turn OFF the ignition.
  2. Re-install the fuel pump relay.
  3. Install a new fuse.
  4. Connect the fuel pump harness to the Body Pass Through connector.
  5. Turn ON the ignition leaving the engine OFF.
  6. Command the fuel pump relay ON using a scan tool.

Is the Fuel Pump fuse open?

--

Go to Step 24

Go to Diagnostic Aids

22
  1. Inspect for a poor connection at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems .
  2. If you find a poor connection, repair the circuit as necessary. Refer to Repairing Connector Terminals in Wiring Systems .

Did you find and correct the condition?

--

Go to Step 29

Go to Step 23

23

Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the action complete?

--

Go to Step 29

--

24
  1. Lower the fuel tank. Refer to Fuel Tank Replacement .
  2. Test the fuel pump harness between the Body Pass Through connector and the fuel pump (sending unit) for a short to ground.
  3. If you find a grounded circuit, repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 29

Go to Step 27

25
  1. Inspect for poor connections at the Body Pass Through connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems .
  2. If you find a poor connection repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 29

Go to Step 26

26
  1. Lower the fuel tank. Refer to Fuel Tank Replacement .
  2. Remove the fuel sending unit jumper harness.
  3. Inspect the harness for damage.
  4. If you find a damaged harness, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 29

Go to Step 27

27
  1. Inspect for poor connections at the fuel tank sending unit. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems .
  2. If you find a poor connection repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 29

Go to Step 28

28

Important: Inspect for poor electrical connections (within the fuel tank) at the fuel pump/sending unit harness connector before replacing the fuel pump.

Replace the fuel pump. Refer to Fuel Tank Fuel Pump Module Replacement .

Is the action complete?

--

Go to Step 29

--

29
  1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
  2. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 30

Go to Step 2

30
  1. Idle the engine until the normal operating temperature is reached.
  2. Select the Diagnostic Trouble Code (DTC) option.

Are any DTCs displayed?

--

Go to the applicable DTC table

Go to Step 31

31

Select the Capture Info option and the Review Info option using the scan tool.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to the applicable DTC table

System OK