GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2003 🢒 CTS - RHD 🢒 Engine 🢒 Engine Electrical 🢒 Fuel Pump Electrical Circuit Diagnosis

Circuit Description

When the ignition switch is turned ON, the engine control module (ECM) 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 ECM is receiving crankshaft position (CKP) sensor reference pulses. If no CKP sensor reference pulses are present, the ECM de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped. The ECM applies a low current signal of approximately 7 volts to the fuel pump relay control circuit with the key ON and the engine OFF. The ECM uses this signal to detect the integrity of the fuel pump relay control circuit.

Diagnostic Aids

Fuel Relay Right Rear Bussed Electrical Center Terminal Identification

Front of vehicle

Left side of vehicle

Control

Fuel pump supply

Right side of vehicle

--

Ignition 1 voltage

Ground

--

Test Description

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

  1. Command both the ON and OFF states. Repeat the commands as necessary. This can be determined by listening for an audible hiss from the fuel pump when the fuel pump relay is commanded ON or a vibration in the fuel feed line.

    2.

  2. This step determines if the condition is located on the coil side or the switch side of the relay.

    3.

  3. This step determines if the fuel pump relay is stuck closed.

    4.

  4. This step tests for a grounded voltage supply circuit. The fuel pump fuse supplies power to fuel pump. Disconnecting the fuel pump in-line harness connector isolates the fuel pump voltage supply circuit.

    5.

  5. This step verifies that the ECM is providing voltage to the fuel pump relay.

    6.

  6. This step verifies that the fuel pump fuse is providing voltage to the fuel pump relay.

    7.

  7. This step tests for an open circuit or a short to ground causing an open MaxiFuse.

    8.

  8. This step bypasses the fuel pump relay in order to activate the fuel pump.

    9.

  9. This step tests for an open in the fuel pump feed circuit between the in-line connector and the fuel pump relay.

    10.

  10. This step tests for an open or high resistance in the fuel pump ground circuit.

    11.

  11. This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump relay ON and OFF with a scan tool.

Does the fuel pump turn ON and OFF?

Go to Intermittent Conditions

Go to Step 3

3

  1. Remove the rear seat. Refer to Rear Seat Cushion Replacement in Seats.

    2. Important: An audible click should be heard.

  2. Command the fuel pump relay ON and OFF with a scan tool.

Do you hear a click when you command the fuel pump relay ON and OFF?

Go to Step 4

Go to Step 9

4

Turn ON the ignition, with the engine OFF.

Does the fuel pump operate continuously?

Go to Step 5

Go to Step 6

5

  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.

Does the fuel pump operate continuously?

Go to Step 20

Go to Step 24

6

Is the fuel pump fuse open?

Go to Step 7

Go to Step 10

7

  1. Disconnect the fuel pump harness in-line connector located near the fuel tank. Refer to Power and Grounding Component Views in Wiring Systems.
  2. Test the supply voltage circuit of the fuel pump for a grounded circuit. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.
  3. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 26

Go to Step 8

8
  1. Lower the fuel tank if necessary. Refer to Fuel Tank Replacement .
  2. Test or inspect the fuel tank electrical harness for the following conditions:
    3. • Damage to the harness
    • A grounded fuel pump voltage supply circuit--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  3. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 26

Go to Step 17

9

  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the fuel pump relay control circuit with a test lamp connected to a ground.
  5. Command the fuel pump ON and OFF with a scan tool.

Did the test lamp illuminate?

Go to Step 18

Go to Step 19

10

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

Does the test lamp illuminate?

Go to Step 12

Go to Step 11

11

  1. Turn OFF the ignition.
  2. Disconnect the fuel pump fuse.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the battery positive side of the fuel pump fuse, with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 21

Go to Step 22

12

Connect a 15-amp fused jumper wire between the battery positive voltage circuit and the fuel pump supply circuit in the fuel pump relay cavity.

Does the fuel pump operate?

Go to Step 18

Go to Step 13

13

  1. Disconnect the fuel pump harness in-line connector located near the fuel tank. Refer to Power and Grounding Component Views in Wiring Systems.
  2. Test the supply voltage circuit of the fuel pump for an open or for high resistance between the fuel pump relay and the in-line connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 14

14

Important: Inspect the fuel pump ground circuit for being tight, corrosion on the terminals, or damage to the wiring harness.

Test the ground circuit of the fuel pump for an open or for high resistance between the body pass through connector and the ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 15

15

Test for an intermittent and for a poor connection at the fuel pump in-line connector to the body pass through connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 16

16

  1. Lower the fuel tank. Refer to Fuel Tank Replacement .
  2. Test or inspect the fuel tank electrical harness for the following conditions:
    3. • Damage to the harness
    • A short to ground
    • An open circuit--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 23

17
  1. Connect all disconnected components.
  2. Install a new fuel pump fuse.
  3. Command the fuel pump ON with a scan tool.

Is the fuel pump fuse open?

Go to Step 23

Go to Intermittent Conditions

18

Test for an intermittent and for a poor connection at the fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 24

19

Test for an intermittent and for a poor connection at the harness of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 25

20

Repair the supply voltage circuit of the fuel pump for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 26

--

21

Repair the battery positive voltage circuit of the fuel pump relay for an open. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 26

--

22

Repair the battery positive voltage circuit of the fuel pump fuse for an open or a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 26

--

23

Important: Inspect for poor connections at the fuel pump, within the fuel tank, before replacing the fuel pump.

  1. Replace the right fuel tank module. Refer to Primary Fuel Tank Module Replacement .
  2. Replace the fuel pump fuse if necessary.

Did you complete the replacement?

Go to Step 26

--

24

Replace the fuel pump relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 26

--

25

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 26

--

26

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2