GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Denali 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC P2636

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P2636: Fuel Pump 2 Flow Insufficient

Circuit/System 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.

Conditions for Running the DTC
    • DTCs P0461, P0462, P0463, P0500, P2067, or P2068 are 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

DTC P2636 is a Type C DTC.

Conditions for Clearing the DTC
    • DTC P2636 is a Type C DTC.
    • The fuel gage will default to empty when this DTC sets.

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 ignition is on or the engine is running while fueling the vehicle, this DTC may set.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Special Tools Required

J 43244 Relay Puller Pliers

Circuit/System Verification
  1. If DTC P2632 is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  2. Turn ON the ignition, with the engine OFF.
  3. Command the fuel pump relay ON and OFF several times with a scan tool. You should either hear or feel the fuel pump relay click with each command. The fuel pump should operate when commanded ON.
  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 data.

Circuit/System Testing

Important: 

   • You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
   • If the fuel level is not between 25-50 percent, add 19 L (5 gal) 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. You should either hear or feel the fuel pump relay click with each command.
    3. ⇒If the fuel pump relay did not clicked when commanded ON and OFF , replace the fuel pump relay.
  3. Remove the fuel pump relay from the underhood electrical center.
  4. Probe the positive voltage supply circuit of the fuel pump relay with a test lamp that is connected to a ground. The test lamp should illuminate.
    5. ⇒If the test lamp did not illuminate, test the positive voltage supply circuit for an open.
  5. Connect a fused jumper wire between the positive voltage supply circuit of the fuel pump relay and the voltage supply circuit of the fuel pump. The fuel pump should operate.
    6. ⇒If the fuel pump did not operate, test the voltage supply circuit of the fuel pump and the ground circuit of the fuel pump for an open.
    ⇒If the positive voltage supply circuit fuse opens, test the voltage supply circuit of the fuel pump for a short to ground.
    ⇒If all circuits tested normal, replace the fuel pump.
  6. With the fused jumper still connected , observed the Fuel Level sensor voltage parameter with a scan tool. The rear fuel level voltage should increase as the pump is operating.
    7. ⇒If the fuel level voltage did not increased, inspect the fuel lines and the fuel sender for a restriction at the rear fuel tank.
  7. Remove the fused jumper and disconnect the outlet hose from the fuel pump. Connect a section of rubber hose with a clamp to the outlet port of the fuel pump. Insert the other end of the hose into an approved container to measure more than 4 liters (1.06 gallons) of fuel. Operate the fuel pump for a total of 2 minutes and measure the fuel in the container. There should be 2.6 liters (0.70 gallons) of fuel.
    8. ⇒If the fuel volume did not measure more than 2.6 liters (0.70 gallons) within the specified time, replace the fuel pump.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Pump Replacement