GM Service Manual Online
For 1990-2009 cars only

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 P2635: Fuel Pump Flow Performance

Diagnostic Fault Information

Circuit

Short to Ground

Open or High Resistance

Short to Voltage

Signal Performance

Fuel Pump High Control

P0231

P023F

P0232

P023F, P2635

Fuel Pump Low Control

--

P023F

--

P023F, P2635

Circuit/System Description

The engine control module (ECM) supplies voltage to the fuel pump flow control module (FPCM) when the ECM detects that the ignition is on. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in crank or run. While this voltage is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel rail pressure.

Conditions for Running the DTC

    •  DTC P0191, P0192, P0193, P0231, P0232, P023F, P064A, P1255 or P06A6 are not active.
    • DTC P0641 has not failed this ignition cycle.
    • Fuel pump control is enabled and the fuel pump control state is normal.
    • The system voltage is greater than 11 volts.
    • The engine has been running for more than 30 seconds.

Conditions for Setting the DTC

This DTC sets when the FPCM detects a predetermined fuel pressure performance degradation between the desired fuel rail pressure and the current estimated fuel rail pressure.

Action Taken When the DTC Sets

DTC P2635 is a Type A DTC.

Conditions for Clearing the DTC

DTC P2635 is a Type A DTC.

Diagnostic Aids

Using the Failure Records data may help locate an intermittent condition. If you cannot duplicate the DTC, the information in the Failure Records can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can help determine how many ignition cycles that the diagnostic test reported a pass and/or a fail.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Fuel System Description

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

Control Module References for scan tool information

Circuit/System Testing

  1. Verify that DTCs P0192, P0193, P0231, P0232, or P023F are not set.
  2. If the DTC is set, refer to DTC P0192 or P0193 or DTC P0231, P0232, or P023F.
  3. Ignition OFF, disconnect the harness connector at the G12 fuel pump.
  4. Ignition ON, test for less than 5.0 Ω between the G12 fuel pump low reference circuit terminal 1 and ground.
  5. If greater than the specified range, test the G12 fuel pump low reference circuit for a high resistance. If the circuit tests normal, replace the K27 FPCM.
  6. Ignition OFF, install a test lamp between the control circuit terminal 2 and the low reference circuit terminal 1.
  7. Ignition ON, command the Fuel Pump Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  8. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K27 FPCM.
    If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K27 FPCM.
  9. Perform the Fuel System Diagnosis to verify proper fuel pressure.
  10. If the fuel pressure is not normal, replace the G12 fuel pump
  11. If all circuits test normal, replace the K27 FPCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for FPCM replacement, setup, and programming