Circuit Description
An ignition voltage circuit and a ground circuit are supplied to the fuel pump control module. When the ignition switch is in the ON position, the fuel pump control module turns ON the fuel pump to full power within 24 ms. This facilitates rapid fuel prime for 500 ms. The engine control module (ECM) supplies a pulse width modulated (PWM) signal to the fuel pump control module on the fuel pump relay control circuit. The fuel pump control module varies the voltage to the fuel pump based on the signal from the ECM. If the fuel pump control module receives no fuel pump control signal from the ECM within 500 ms, the fuel pump control module will turn OFF output to the fuel pump.
At idle speed, the fuel pump control module sets the voltage potential to the fuel pump to 9.5 volts. This reduces fuel pump noise and vehicle system power requirements. When higher fuel volume is required, such as engine operation above idle, the fuel pump control module increases the voltage potential to the fuel pump to battery voltage.
The fuel pump control module also supplies the fuel pump speed output circuit and the fuel pump motor low reference circuit, which allows for enhanced fuel pump diagnostics. Therefore, the fuel pump control module is capable of diagnosing itself, the fuel pump relay control circuit, and the fuel pump performance. The diagnostic information is communicated from the fuel pump control module to the ECM through the fuel pump speed control feedback signal circuit.
If the ECM detects an output driver failure in the fuel pump control module, DTC P1251 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1251 Fuel Pump Speed Control Module Performance
Conditions for Running the DTC
| • | The fuel pump is controlled by the fuel pump control module. |
| • | The ignition voltage is between 6-18 volts. |
| • | The ignition ON time is more than 2 seconds. |
| • | DTC P1251 runs continuously once the above conditions have been met. |
Conditions for Setting the DTC
| • | The ECM detects an output driver failure in the fuel pump control module. |
| • | The above conditions are present for more than 2 seconds. |
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. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Did the DTC fail this ignition? | Go to Step 3 | Go to Intermittent Conditions |
3 | Test the fuel pump motor low reference circuit and the ground circuit of the fuel pump control module for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 5 | Go to Step 4 |
4 | Replace the fuel pump control module. Refer to Fuel Pump Control Module Replacement . Did you complete the replacement? | Go to Step 5 | -- |
5 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 6 |
6 | 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 in Vehicle DTC Information | System OK |
