Circuit Description
The powertrain control module (PCM) 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 crankshaft reference pulses are received. If no crankshaft reference pulses are received, the control module de-energizes the fuel pump.
The fuel pump relay control circuit is pulled up to 2.5 volts within the PCM using a bypass resistor that is connected internally to ignition voltage. This resistor allows the PCM to detect a high voltage condition if the fuel pump control circuit is open when the pump relay is not commanded ON. The control module monitors the voltage on the fuel pump relay control circuit. If the PCM detects a low voltage condition on the control circuit with the engine cranking or running, DTC P0628 sets.
DTC Descriptors
This diagnostic procedure supports the following DTC:
P0628 Fuel Pump Relay Control Circuit Low Voltage
Conditions for Running the DTC
| • | The engine speed is more than 80 RPM. |
| • | The engine controls ignition relay voltage is between 10-18 volts. |
| • | The PCM has commanded the fuel pump relay ON and OFF at least once during the ignition cycle. |
| • | DTC P0628 runs continuously once the above conditions have been met. |
Conditions for Setting the DTC
| • | The PCM detects the voltage on the fuel pump relay control circuit is less than 2.21 volts. |
| • | The condition exists for less than 1 second. |
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 3 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
| • | 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.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
2 |
Does the fuel pump relay turn ON and OFF with each command? | Go to Step 3 | Go to Step 4 |
3 |
Did the DTC fail this ignition? | Go to Step 4 | Go to Intermittent Conditions |
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 in Wiring Systems. 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 PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 8 | -- |
8 |
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? | System OK | |
