Circuit Description
The fuel pump relay is located in the underhood fuse block (UBFB). The engine control module (ECM) provides a ground to the fuel pump relay coil whenever the engine is cranking or running. When the fuel pump relay is commanded OFF, circuit not grounded, the voltage level at the ECM should be high. When the fuel pump relay is commanded ON, circuit grounded, the voltage level at the ECM should be low. The ECM fuel pump relay feedback circuit uses a pull-up voltage, 2.6-4.6 volts, which allows the ECM to individually differentiate between an open, a short to ground, or a short to voltage. During engine crank, the ECM will command the fuel pump relay OFF for a very short amount of time. During this time it will test for an open/low voltage condition. This test is only performed once during engine crank. DTC P0629 will set if the ECM detects lower than normal feedback voltage when the fuel pump relay is commanded OFF with the engine cranking.
DTC Descriptor
This diagnostic procedure supports the following DTC:
P0629 Fuel Pump Relay Control Circuit High Voltage
Conditions for Running the DTC
| • | The engine speed is more than 40 RPM. |
| • | The system voltage is between 7.5-15 volts. |
Conditions for Setting the DTC
| • | The control module detects an incorrect voltage on the control circuit of the fuel pump relay. |
| • | The condition exists for less than 1 second. |
| • | DTC P0629 runs continuously once the above conditions have been met. |
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. |
Diagnostic Aids
The fuel pump relay coil resistance is 70-120 ohms.
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: 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 in Vehicle DTC Information |
2 |
Important: An audible click should be heard. Does the fuel pump relay turn ON and OFF with each command? | Go to Step 3 | Go to Step 4 |
3 |
Does the DTC fail this ignition? | Go to Step 4 | Go to Intermittent Conditions |
Does the test lamp remain illuminated? | Go to Step 5 | Go to Step 6 | |
5 | Test the control circuit of the fuel pump relay for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 10 | Go to Step 7 |
6 | Inspect for poor connections at the fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 10 | Go to Step 8 |
7 | Inspect for poor connections at the harness connectors of the control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 10 | Go to Step 9 |
8 | Replace the fuel pump relay. Did you complete the replacement? | Go to Step 10 | -- |
9 | Replace the engine control module (ECM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 10 | -- |
10 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 11 |
11 | 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 |
