GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 XLR 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 DTC P2636

System Description

The fuel pump supplies a small amount of pressurized fuel through the auxiliary fuel feed pipe to the siphon jet pump inside the right fuel tank. The pressurized fuel creates a venturi action inside the siphon jet pump. The venturi action causes the fuel to be drawn out of the right fuel tank. The fuel transfers from the right fuel tank to the left fuel tank through the auxiliary fuel return pipe. The auxiliary fuel return pipe contains an anti-siphon hole in order to prevent fuel from siphoning from the left fuel tank into the right fuel tank. Both the auxiliary fuel feed pipe and the auxiliary fuel return pipe are located inside the convoluted stainless steel crossover hose.

The right fuel tank module contains a secondary fuel pressure regulator. The secondary fuel pressure regulator has a lower set point than the primary regulator in order to allow fuel to flow to the siphon jet pump on the right fuel tank module. When the engine is shut off, the pressure in the feed pipes immediately drops to the secondary regulator set point. This prevents the siphon jet pump from operating and in turn prevents the equalization of the left and right fuel tanks. The secondary fuel pressure regulator maintains fuel pressure in the auxiliary fuel feed pipe which reduces the time to prime the siphon jet pump. The pressurization also reduces fuel vaporization and boiling in the auxiliary fuel feed pipe.

The left fuel level sensor and the right fuel level sensor change resistance in response to fuel level. The engine control module (ECM) monitors the signal circuit of the left fuel level sensor and the signal circuit of the right fuel level sensor in order to determine the fuel level. When the fuel tanks are full, the resistances of both fuel level sensors are high, and the ECM senses a high signal voltage on both the signal circuit of the left fuel level sensor and the signal circuit of the right fuel level sensor. When the fuel tanks are empty, the resistances of the fuel level sensors are low, and the ECM senses a low signal voltage. The ECM uses the signal circuits of the left fuel level sensor and the right fuel level sensor in order to calculate the percentage of remaining fuel in the tanks. The ECM sends the fuel level percentage via the Class 2 serial data circuit to the instrument cluster in order to control the fuel gage.

This diagnostic tests for damage or restriction in the fuel system affecting the transfer of fuel from the right fuel tank to the left fuel tank. If the ECM detects that the right fuel level is more than a predetermined amount of the left fuel level, DTC P2636 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2636 Fuel Transfer Pump Flow Insufficient

Conditions for Running the DTC
    • The ignition is ON.
    • DTC P2636 runs continuously once the above conditions have been met.

Conditions for Setting the DTC
    • The ECM detects that the left fuel tank is less than 6.25 liters (1.7 gallons) and the right fuel tank is more than 33 liters (8.7 gallons).
    • The above condition is met for 1 minute.

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.

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.

Step

Action

Value(s)

Yes

No

Schematic Reference: Fuel Hose/Pipes Routing Diagram

1

Did you perform the Diagnostic System Check-Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Turn ON the ignition, with the engine OFF.
  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 Step 3

Go to Intermittent Conditions

3

Observe the Fuel Level Sensor Left parameter with a scan tool.

Is the Fuel Level Sensor Left parameter less than the specified value?

0.8 V

Go to Step 4

Go to Step 5

4

Add the specified amount of fuel.

Did you complete the action?

15 L (4 gal)

Go to Step 5

--

5

    Important: The engine coolant temperature must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.

  1. Install a J 34730-1A Fuel Pressure Gage. Refer to Fuel Pressure Gage Installation and Removal .
  2. Turn ON the ignition, with the engine OFF.

    3. Important: The fuel pump may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

  3. Command the fuel pump ON with a scan tool.
  4. Observe the J 34730-1A with the fuel pump running.

Is the fuel pressure within the specified value?

380-427 kPa (55-62 psi)

Go to Step 6

Go to Fuel System Diagnosis

6

Observe the Fuel Level Sensor Right parameter.

Is the Fuel Level Sensor Right parameter less than the specified value?

1 V

Go to Step 7

Go to Step 9

7

Fill the fuel system until the Fuel Level Sensor Right parameter is more than the specified value.

Did you complete the action?

1 V

Go to Step 8

--

8

Drain the left fuel tank until the Fuel Level Sensor Left parameter is less than the specified value. Refer to Fuel Tank Draining .

Did you complete the action?

1.5 V

Go to Step 9

--

9
  1. Start the engine.
  2. Observe the Fuel Level Sensor Left and the Fuel Level Sensor Right parameters with a scan tool for 5 minutes.

Does the Fuel Level Sensor Right parameter decrease while the Fuel Level Sensor Left parameter increases?

--

Go to Intermittent Conditions

Go to Step 10

10
  1. Remove the fuel tank crossover tube/hose. Refer to Fuel Tank Crossover Tube Replacement .
  2. Inspect the auxiliary fuel feed pipe and the auxiliary fuel return pipe inside of the crossover tube/hose for a restriction.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 11

11
  1. Connect the J 41413-200 Evaporative Emissions System Tester (EEST) to one end of the 5/16 inch auxiliary fuel feed pipe inside of the crossover hose using the appropriate hose and the J 41413-311 Brass Cone Adapter from the J 41413-300 EVAP Cap/Plug Kit.
  2. Apply nitrogen to the auxiliary fuel feed pipe.
  3. Cap the other end of the 5/16 inch auxiliary fuel feed pipe inside of the crossover hose using the J 41413-306 Small Red Cap from the J 41413-300.
  4. Observe the flow meter on the J 41413-200 .

Does the flow meter indicate a leak?

--

Go to Step 20

Go to Step 12

12
  1. Connect the J 41413-200 to one end of the 3/8 inch auxiliary fuel return pipe inside of the crossover hose using the appropriate hose and the J 41413-311 from the J 41413-300 .
  2. Apply nitrogen to the auxiliary fuel return pipe.
  3. Cap the other end of the 3/8 inch auxiliary fuel return pipe inside of the crossover hose using the J 41413-307 Small Black Cap from the J 41413-300 .
  4. Observe the flow meter on the J 41413-200 .

Does the flow meter indicate a leak?

--

Go to Step 20

Go to Step 13

13

Inspect for damaged O-rings at the crossover hose to fuel tank connections.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 14

14
  1. Connect the J 41413-200 to the 5/16 inch auxiliary fuel feed pipe inside of the left fuel tank using the appropriate hose and the J 41413-311 from the J 41413-300 .
  2. Apply nitrogen to the auxiliary fuel feed pipe.
  3. Observe the flow meter on the J 41413-200 .

Does the flow meter indicate a leak?

--

Go to Step 16

Go to Step 15

15
  1. Connect the J 41413-200 to the 5/16 inch auxiliary fuel feed pipe inside of the right fuel tank using the appropriate hose and the J 41413-311 from the J 41413-300 .
  2. Apply nitrogen to the auxiliary fuel feed pipe.
  3. Observe the flow meter on the J 41413-200 .

Does the flow meter indicate a leak?

--

Go to Step 17

Go to Step 19

16
  1. Remove the left fuel tank module. Refer to Fuel Tank Fuel Pump Module Replacement - Left Side .
  2. Inspect the auxiliary fuel feed and return pipes for damage or restriction.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

17
  1. Remove the right fuel tank module. Refer to Fuel Tank Fuel Pump Module Replacement - Right Side .
  2. Inspect the auxiliary fuel feed and return pipes for damage or restriction.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

18

Replace the left fuel tank module. Refer to Fuel Tank Fuel Pump Module Replacement - Left Side .

Did you complete the replacement?

--

Go to Step 21

--

19

Replace the right fuel tank module. Refer to Fuel Tank Fuel Pump Module Replacement - Right Side .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the fuel tank crossover tube/hose. Refer to Fuel Tank Crossover Tube Replacement

Did you complete the replacement?

--

Go to Step 21

--

21
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Turn ON the ignition, with the engine OFF.
  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 Step 2

Go to Step 22

22

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 in Vehicle DTC Information

System OK