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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 SRX 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Fuel Pump Electrical Circuit Diagnosis

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.

Circuit/System Description

The engine control module (ECM) provides ignition voltage to the coil side of the fuel pump relay whenever the engine is cranking or running. The control module enables the fuel pump relay as long as the engine is cranking or running, and ignition system reference pulses are received. If no ignition system reference pulses are received, the control module turns OFF the fuel pump. The fuel pump relay control circuit is equipped with a feedback circuit that is pulled up to 2.5 volts within the ECM. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

Diagnostic Aids

The following conditions may cause the fuel pump fuse to open:

    • The fuse is faulty.
    • There is an intermittent short to ground in the supply voltage circuit of the fuel pump.
    • The fuel pump has an intermittent internal condition.
    • If the condition is intermittent, move the related harnesses and connectors, with the engine operating, while monitoring the circuit status for the component with a scan tool. The circuit status parameter changes from OK or Indeterminate to Fault if there is a condition with the circuit or a connection.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls 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

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

    Important: Fuel pump DTCs may set when using the Fuel Pump output control.

  1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump operate for 3-5 seconds and then turn OFF.
  2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing
  1. Ignition OFF, the fuel pump should not be operating.
    2. ⇒If the fuel pump operates continuously, test for a short to voltage in supply voltage circuit of the fuel pump. If the circuit/connections test normal, replace the fuel pump relay.
  2. Test the fuel pump fuse. The fuse should not be open.
    3. ⇒If the fuel pump fuse is open, test for a short to ground in the supply voltage circuit of the fuel pump. If the circuit/connections test normal, replace the fuel pump.
  3. Ignition OFF, remove the fuel pump relay from the electrical center.
  4. Ignition ON, test for battery voltage between the B+ voltage circuit of the fuel pump relay and ground.
    5. ⇒If less than B+, repair the B+ voltage circuit of the fuel pump relay for an open/high resistance.
  5. Connect a 20A fused jumper wire between the B+ circuit of the fuel pump relay and the supply voltage circuit of the fuel pump. The fuel pump should operate.
    6. ⇒If the fuel pump does not operate, test for the following conditions:
    • An open/high resistance in the supply voltage circuit of the fuel pump
    • An open/high resistance in the ground circuit of the fuel pump
    ⇒If the above circuit/connections test normal, replace the fuel pump.
  6. If all circuit/connections test normal, test or replace the fuel pump relay.

Component Testing
  1. Measure for 70-110 ohms of resistance between terminals 85 and 86 of the fuel pump relay.
    2. ⇒If the resistance is not within the specified range, replace the fuel pump relay.
  2. Measure for infinite resistance between the following terminals of the fuel pump relay:
    3. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒If continuity is detected, replace the fuel pump relay.
  3. Connect a 20A fused jumper wire from the positive terminal of the battery to relay terminal 85. Connect a jumper wire from the negative terminal of the battery to relay terminal 86. Measure for less than 2 ohms between terminals 30 and 87 of the relay.
    4. ⇒If the resistance measures more than 2 ohms, replace the fuel pump relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Primary Fuel Tank Module Replacement
    •  Relay Replacement