GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The fuel pump is located on the left frame rail between the fuel tanks. The engine control module (ECM) provides ignition positive voltage to the coil side of the fuel pump relay. The ECM energizes the fuel pump relay, which applies power to the fuel transfer pump. Fuel is transferred from the rear fuel tank to the front fuel tank in order to ensure all of the usable fuel volume is available to the engine. If the ECM commands the transfer fuel pump ON and a predetermined change in the front and rear fuel level sensors does not occur, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2636 Fuel Pump 2 Flow Insufficient

Conditions for Running the DTC

    • DTC P0500 is not set.
    • The engine is running.
    • The vehicle speed is 0 km/h (0 mph).
    • The primary fuel level is less than 25 liters (6.6 gallons).
    • The secondary fuel level is between 3-10 liters (0.8-2.6 gallons).
    • The above conditions are met for 20 seconds before the fuel transfer pump is commanded ON.
    • The fuel transfer pump is commanded ON for 120 seconds.

Conditions for Setting the DTC

The ECM detects a primary fuel level increase and a secondary fuel level decrease of less than 2.6 liters (0.70 gallons) each, within 120 seconds.

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.
    • The fuel gage will be commanded to empty.

Conditions for Clearing the DTC

    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

    • When outside temperatures are below 0°C (32°F), the fuel tank pickup screen may ice over from water in the fuel tank.
    • If the engine is running while fueling the vehicle, this DTC may set.
    • The fuel will default to empty when this DTC sets.

Test Description

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

  1. This step determines if the condition is on the coil side or the switch side of the fuel pump relay.

  2. This step verifies the fuel transfer pump operation. If the test lamp flashes, the fuel transfer pump and circuits are OK.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Is DTC P0461, P0462, P0463, P2067, or P2068 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3

Important: The fuel level must be between 25-50 percent in order to perform this diagnostic procedure. If the fuel level is not within this range, misdiagnosis will occur.

  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 relay click?

--

Go to Step 9

Go to Step 4

4

  1. Remove the fuel pump relay from the underhood electrical center.
  2. Probe the ground circuit of the fuel pump relay with a test lamp that is connected to battery voltage. Refer to Probing Electrical Connectors and Circuit Testing .

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 25

5

  1. Probe the fuel pump relay control circuit with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors .
  2. Command the fuel pump relay ON and OFF with a scan tool.

Does the test lamp turn ON and OFF?

--

Go to Step 22

Go to Step 6

6

Does the test lamp remain illuminated?

--

Go to Step 7

Go to Step 8

7

Test the fuel pump relay control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 24

8

Test the fuel pump relay control circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 24

9

Command the fuel transfer pump ON with a scan tool.

Does the fuel transfer pump operate?

--

Go to Step 17

Go to Step 10

10

  1. Remove the fuel pump relay from the underhood electrical center.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the battery voltage circuit of the fuel pump relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 12

11

Connect a fused jumper wire between the fuel pump relay battery voltage circuit and the fuel pump supply voltage circuit.

Does the fuel pump operate?

--

Go to Step 22

Go to Step 15

12

Is the battery positive voltage fuse open?

--

Go to Step 13

Go to Step 27

13

Test the battery voltage circuit of the fuel pump relay for a short to ground.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 14

14

Test the fuel pump supply voltage circuit for a short to ground.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 23

15

Test the fuel transfer pump supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 16

16

Probe the ground circuit of the fuel transfer pump with a test lamp that is connected to battery voltage.

Does the test lamp illuminate?

--

Go to Step 23

Go to Step 26

17

Observe the fuel level sensor rear tank voltage parameter with a scan tool.

Is the voltage more than the specified value?

1 V

Go to Step 19

Go to Step 18

18

Add the specified amount of fuel to the rear fuel tank.

Did you complete the action?

19 L (5 gal)

Go to Step 19

--

19

  1. Connect a fused jumper wire between the fuel pump relay battery voltage circuit and the fuel pump voltage supply circuit.
  2. Observe the Fuel Level sensor voltage parameter with a scan tool.

Does the rear fuel level sensor voltage parameter decrease as the fuel pump is operating?

--

Go to Step 20

Go to Step 21

20

  1. Disconnect the outlet hose from the fuel transfer pump.
  2. Connect a section of rubber hose with a clamp to the outlet port of the transfer pump.
  3. Insert the other end of the rubber hose into a container to measure more than 4 liters (1.06 gallons).
  4. Operate the transfer pump with a scan tool for a total of 120 seconds.
  5. Measure the fuel in the container.

Does the fuel volume measure more than the specified value?

2.6 L (0.70 gal)

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 21

21

Inspect for the following conditions:

    • A restriction in the fuel lines between the front and rear fuel tanks
    • The rear fuel sender for a restriction

Did you find and correct the condition?

--

Go to Step 31

Go to Step 29

22

Inspect for poor connections at the harness connector of the fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 28

23

Inspect for poor connections at the harness connector of the fuel transfer pump. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 29

24

Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 30

25

Repair the open ground circuit of the fuel pump relay. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 31

--

26

Repair the open ground circuit of the fuel transfer pump. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 31

--

27

Repair the open battery voltage circuit of the fuel pump relay. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 31

--

28

Replace the fuel pump relay.

Did you complete the replacement?

--

Go to Step 31

--

29

Replace the fuel transfer pump. Refer to Fuel Pump Replacement .

Did you complete the replacement?

--

Go to Step 31

--

30

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 31

--

31

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Diagnostic Aids

Go to Step 32

32

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK