GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 DTC 🢒 DTC P0628

Circuit 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. If the ECM detects the control circuit voltage is less than a predetermined voltage when commanded ON, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0628 Fuel Pump Relay Control Circuit Low Voltage

Conditions for Running the DTC
    • The fuel pump relay is commanded ON.
    • The ignition 1 voltage is more than 10.5 volts.
    • DTC P0628 runs continuously once the above conditions are met.

Conditions for Setting the DTC
    • The ECM detects that the fuel pump relay control circuit is shorted to ground.
    • The condition exists for less than 4 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
    • 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 emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
    • The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views .
    • If the condition is intermittent, move the related harnesses and connectors while monitoring the circuit status for the component in the Output Driver Module (ODM) data list with a scan tool. The circuit status parameter changes from OK to Fault if there is a condition with the circuit or a connection.
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step verifies that the control module is providing voltage to the fuel pump relay.

DTC P0628 Fuel Pump Relay Control Circuit Low Voltage

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Important: 

   • DTCs P1629, P1630, P1631, and P2105 may cause this DTC to set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
   • Additional DTCs may set when using the fuel pump output control.

  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump ON and OFF with a scan tool.

Does the fuel pump relay turn ON and OFF with each command?

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  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 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control circuit of the fuel pump relay with a test lamp connected to a good ground.
  5. Command the fuel pump ON and OFF with a scan tool.

Does the test lamp turn ON and OFF?

Go to Step 6

Go to Step 5

5

Test the control circuit of the fuel pump relay for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 7

6

Replace the fuel pump relay.

Did you complete the replacement?

Go to Step 8

--

7

Replace the engine control module (ECM). Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 8

--

8
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  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 9

9

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

System OK