P2636

DTC P2636

Circuit 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.