GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Riviera 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Fuel Pump Electrical Circuit Diagnosis

Object Number: 431001 Size: MF
Engine Controls Components
Engine Controls Schematics
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 battery positive voltage to the fuel pump control module. 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 the scan tool output controls function.

The PCM alters fuel pump speed by varying the duty cycle on the fuel pump speed control PWM circuit to the fuel pump control module. The fuel pump speed control PWM circuit duty cycle is set at 33% under normal conditions. When higher fuel volume is required due to increased engine load (MAP sensor value over 90 kPa), the PCM switches the fuel pump speed control PWM circuit duty cycle to 100%. The fuel pump control module increases the voltage the in-tank fuel pump, allowing a higher volume of fuel to be delivered to the fuel rail at the higher duty cycle. The PCM also compensates for low system voltage by switching the fuel pump control circuit PWM duty cycle to 100%.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through the wire insulation or a wire broken insideof the insulation.

Check for a poor connection or a 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 Table:

  1. Fuel pressure between the specified values is sufficient for the vehicle to start. If directed to this table from the Engine Cranks But Will Not Run table, continue diagnosis with Engine Cranks But Will Not Run.

    2.

  2. Ensures that the fuel pump speed control PWM circuit and the PCM are capable of controlling fuel pump speed.

    3.

  3. Verifies that the fuel pump high and low circuits are OK between the fuel pump control module and the fuel pump, and that the fuel pump can deliver adequate pressure to the fuel rail.

    4.

  4. Checks the feed circuit to the fuel pump control module. Commands the Fuel Pump Speed and allows only a 2 second time in the commanded state, using a scan tool.

    5.

  5. Ensures that the Fuel pump PWM Control circuit is not shorted to ground.

    6.

  6. Checks the battery positive voltage circuit to the fuel pump relay contacts.

    7.

  7. Checks the ground circuit for the fuel pump relay coil.

    8.

  8. Ensures that the fuel pump relay control circuit is OK and that the PCM is capable of controlling the fuel pump relay. Commanding the fuel pump relay allows only a 2 second ON time using a scan tool.

    9.

  9. Checks the fuel pump relay control circuit for a short to ground.

    10.

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

  11. Determines whether the problem is being caused by an open in the fuel pump high circuit or the fuel pump low circuit.

    12.

  12. Ensures that the fuel pump PWM control circuit is OK and that the PCM can control the fuel pump speed control circuit. Commands the fuel pump speed and allows only a 2 second time in the commanded state, using a scan tool.

    13.

  13. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Is DTC P0230 set?

--

Go to DTC P0230 Fuel Pump Relay Control Circuit

Go to Step 3

3

  1. Install a fuel pressure gauge.
  2. Turn ON the ignition switch.
  3. Select Special Functions on the scan tool.
  4. Select Engine Output controls on the scan tool.
  5. Select Fuel Pump on the scan tool.

    6. Important: Ensure all fuel lines are connected.

  6. Observe the pressure gauge while commanding the fuel pump ON with the scan tool.

Is fuel pressure indicated at the specified value?

333-376 kPa (48-55 psi)

Go to Step 4

Go to Step 5

4

Important:: If the engine cranks but will not run, continue with Engine Cranks but Does Not Run .

  1. Start the engine.
  2. Select Engine Output Controls with the scan tool.
  3. Select Fuel Pump Speed with the scan tool.
  4. Observe the pressure gauge while using the scan tool to switch fuel pump speed between normal and high.

Does the fuel pressure increase slightly when high fuel pump speed is selected?

--

System OK

Go to Step 31

5

  1. Turn OFF the ignition switch.
  2. Disconnect the fuel pump control module.
  3. Connect a fused jumper between the fuel pump high circuit (fuel pump control module harness connector terminal 6) and B+.
  4. Connect a second jumper between the fuel pump low circuit (fuel pump control module harness terminal 5) and chassis ground.
  5. Observe the fuel pressure gauge.

Is fuel pressure indicated at the specified value?

333-376 kPa (48-55 psi)

Go to Step 6

Go to Step 26

6

  1. Disconnect the jumpers from the fuel pump control module connector.
  2. Connect a test lamp between the fuel pump control module feed circuit (fuel pump control module harness connector terminal 8) and chassis ground.
  3. Turn ON the ignition switch.
  4. Command the fuel pump ON using the scan tool in Engine Output Controls.
  5. Observe the test lamp.

Is the test lamp ON?

--

Go to Step 7

Go to Step 13

7

Probe the fuel pump control module ground circuit (fuel pump control module harness connector terminal 4) with a test lamp to B+.

Is the test lamp ON?

--

Go to Step 8

Go to Step 25

8

  1. Turn OFF the ignition switch.
  2. Disconnect the PCM.
  3. Probe the fuel pump PWM control circuit at the PCM connector with a test lamp to B+.

Is the test lamp ON?

--

Go to Step 9

Go to Step 10

9

Locate and repair the short to ground in the fuel pump PWM control circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 39

--

10
  1. Turn OFF the ignition switch.
  2. Reconnect the PCM.
  3. Turn ON the ignition switch.
  4. Install a J 39200 Digital Multimeter to measure voltage between the fuel pump PWM control circuit (fuel pump control module connector terminal 7) and the fuel pump control module ground circuit (fuel pump control module harness connector terminal 4).
  5. Select special functions on the scan tool.
  6. Select fuel pump in engine output controls, using the scan tool.
  7. Command the fuel pump ON using the scan tool.

Does the voltage measure greater than the specified value while the fuel pump is commanded ON?

8V

Go to Step 11

Go to Step 38

11
  1. Turn OFF the ignition switch.
  2. Reconnect the fuel pump control module electrical connector.
  3. Turn ON the ignition switch.
  4. Backprobe between the fuel pump high circuit (fuel pump control module connector terminal 6) and the fuel pump low circuit (fuel pump control module connector terminal 5), using a scan tool.
  5. Select special functions on the scan tool.
  6. Select engine output controls on the scan tool.
  7. Select fuel pump on the scan tool.
  8. Command the fuel pump ON.

Is the test lamp ON while the fuel pump relay is commanded ON?

--

Go to Step 12

Go to Step 34

12
  1. Check for poor connections at the fuel pump control module.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Step 39

Go to Diagnostic Aids

13

  1. Turn OFF the ignition switch.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition switch.
  4. Probe the fuel pump relay battery positive voltage circuit with a test lamp to ground.

Is the test lamp ON?

--

Go to Step 14

Go to Step 19

14

Connect the test lamp between the fuel pump relay battery positive voltage circuit and the fuel pump relay ground circuit.

Is the test lamp ON?

--

Go to Step 15

Go to Step 20

15

  1. Connect the test lamp between the fuel pump relay control circuit and the fuel pump relay ground circuit.
  2. Command the fuel pump ON using the scan tool in engine output controls.

Is the test lamp ON with the fuel pump commanded ON?

--

Go to Step 16

Go to Step 21

16
  1. Connect a jumper between the fuel pump relay battery positive voltage circuit and the fuel pump control module feed circuit.
  2. Probe the fuel pump control module feed circuit at the fuel pump control module feed harness connector terminal 8 with a test lamp to ground.

Is the test lamp ON?

--

Go to Step 17

Go to Step 24

17
  1. Check for a loose terminal connection at the fuel pump relay.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Is the action complete?

--

Go to Step 39

Go to Step 18

18

Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement .

Is the action complete?

--

Go to Step 39

--

19

Locate and repair open in the fuel pump relay battery positive voltage circuit. Refer to Wiring Repairs .

Is action complete?

--

Go to Step 39

--

20

Locate and repair open in the fuel pump relay ground circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 39

--

21

  1. Turn OFF the ignition switch.
  2. Disconnect the PCM.
  3. Probe the fuel pump relay control circuit at the PCM connector with a test lamp to B+.

Is the test lamp ON?

--

Go to Step 22

Go to Step 23

22

Locate and repair short to ground in the fuel pump relay control circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 39

--

23
  1. Check for the following conditions:
    2. • Fuel pump relay control circuit open between the fuel pump relay and the PCM.
    • Poor fuel pump relay control circuit terminal connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Step 39

Go to Step 38

24

Locate and repair open in fuel pump control module feed circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 39

--

25

Locate and repair open or short to voltage in fuel pump control module ground circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 39

--

26

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

Is the fuel pump running?

--

Go to Fuel System Pressure Test (VIN 1)

Go to Step 27

27
  1. Leave the fuel pump high circuit jumpered to B+ and the fuel pump low circuit jumpered to ground at the fuel pump control module connector.
  2. Remove the modular fuel sender access cover. Refer to Fuel Sender Access Panel .
  3. Disconnect the modular fuel sender electrical connector at the fuel tank.
  4. Connect a test lamp between the fuel pump high circuit and the fuel pump low circuit at the modular fuel sender harness connector.

Is the test lamp ON?

--

Go to Step 36

Go to Step 28

28

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

Is the test lamp ON?

--

Go to Step 30

Go to Step 29

29

Locate and repair open or short to ground in the fuel pump high circuit. Refer to Wiring Repairs . Is the action complete?

--

Go to Step 39

--

30

Locate and repair open in the fuel pump low circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 39

--

31

  1. Backprobe between the fuel pump PWM control circuit control circuit (fuel pump control module terminal 7) and the fuel pump control module feed circuit (fuel pump control module terminal 8) using a test lamp.
  2. Select fuel pump speed in engine output controls with the scan tool and engine idling.
  3. Observe the test lamp while switching fuel pump speed between normal and high.

Is the test lamp ON with Normal selected and OFF with High selected?

--

Go to Step 32

Go to Step 33

32
  1. Backprobe to measure voltage between the fuel pump low circuit (fuel pump control module terminal 5) and the fuel pump high circuit (fuel pump control module terminal 6), using a J 39200 Digital Multimeter.
  2. Select fuel pump speed in engine output controls with the scan tool and engine idling.
  3. Observe the voltage on the digital multimeter while switching fuel pump speed between normal and high:
    4. • Normal speed voltage is the first value shown.
    • High speed voltage is the second value shown.

Does the voltage measure near the specified values?

8V

B+

Go to Step 36

Go to Step 34

33
  1. Check for the following conditions:
    2. • Fuel pump PWM control circuit shorted to voltage or open between the fuel pump control module and the PCM.
    • Poor fuel pump PWM control circuit terminal connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Step 39

Go to Step 38

34
  1. Check for poor terminal connections at the fuel pump control module.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Step 39

Go to Step 35

35

Replace the fuel pump control module. Refer to Fuel Pump Control Module Replacement .

Is the action complete?

--

Go to Step 39

--

36
  1. Check for poor terminal connections at the fuel pump.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Step 39

Go to Step 37

37

Replace the fuel sender assembly. Refer to Fuel Sender Assembly Replacement .

Is the action complete?

--

Go to Step 39

--

38

Important: : The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is action complete?

--

Go to Step 39

--

39
  1. Turn ON the ignition switch
  2. Select fuel pump in engine output controls using a scan tool.
  3. Observe the fuel pressure gauge while turning the fuel pump ON with the scan tool.

Is fuel pressure indicated at the specified value?

333-376 kPa (48-55 psi)

Go to Step 40

Go to Step 5

40
  1. Select fuel pump speed in engine output controls with the scan tool with the engine idling.
  2. Observe the fuel pressure gauge while using the scan tool to switch fuel pump speed between normal and high.

Does the fuel pressure increase slightly when high fuel pump speed is selected?

--

System OK

Go to Step 31