Fuel Pump Electrical Circuit Diagnosis EFI
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Engine Controls (Cell 22: Fuel Controls 1)
Circuit Description
When the key is in turned ON, the PCM energizes the fuel pump relay which sends voltage to the lift pump. The lift pump remains ON during the glow plug cycle. If the engine is not started immediately after the glow plug cycle, the PCM shuts the fuel lift pump OFF and waits until the engine starts. As a backup system to the fuel pump relay, the fuel lift pump can also be turned ON by the fuel pump/oil pressure switch. When the engine oil pressure reaches 28 kPa (4 psi), and the fuel pump relay does not complete the circuit, the fuel pump/oil pressure switch will close and complete the circuit to run the fuel lift pump.
Diagnostic Aids
Possible long crank times or a poor performance problem will exist.
Test Description
The number(s) below refer to step number(s) on the Diagnostic Table.
-
Checks for proper operation of the fuel pump.
-
Checks the operation of the fuel pump by supplying 12 volts to the fuel pump control circuit.
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Check the battery feed circuit to the fuel pump relay.
-
Checks for proper operation of the fuel pump relay.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the Scan Tool Capture Info in order to record the Freeze Frame and the failure records for reference, as the data will be lost when the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the fuel pump operate during the glow plug cycle? | -- | |||
Apply a 12 volt fused jumper to the fuel pump test terminal. Does the fuel pump operate? | -- | |||
4 |
Does the fuel pump operate the during glow plug cycle and then stop? | -- | ||
Is the test light ON? | -- | |||
6 | Connect a test light between the fuel pump relay battery feed circuit harness connector and ground. Is the test light ON? | -- | ||
7 |
Is the test light ON during glow plug cycle and then OFF? | -- | ||
8 | Check for a poor connection at the fuel pump relay control connector terminal. Was a problem found? | -- | ||
9 | Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement. Is the action complete? | -- | ||
Does the engine continue to run? | -- | |||
11 |
Is the test light ON? | -- | ||
12 |
Is the test light ON? | -- | ||
13 | With a test light connected to B+ probe the fuel pump ground terminal (vehicle side) of the chassis harness fuel pump connector. Is the test light ON? | -- | ||
14 | Repair the open in the battery feed circuit to the fuel pump relay harness connector terminal. Is the action complete? | -- | --
| |
15 | Repair the open in the fuel pump relay ground circuit. Is the action complete? | -- | --
| |
16 |
Was a problem found? | -- | ||
17 | Check the oil pressure switch harness connector terminals for a poor connection. Was a problem found? | -- | ||
18 | Replace the oil pressure switch. Refer to Engine Oil Pressure Sensor and/or Switch Replacement . Is the action complete? | -- | -- | |
19 | Replace the fuel pump. Refer to Fuel Lift Pump Replacement . Is the action complete? | -- | -- | |
20 | Repair the open between the fuel pump test terminal and the fuel pump feed circuit at the fuel pump harness connector. Is the action complete? | -- | -- | |
21 | Repair the open in the fuel pump harness ground circuit. Is the action complete? | -- | -- | |
22 | Repair the circuit as necessary. Is the action complete? | -- | -- | |
23 | Repair the connection as necessary. Is the action complete? | -- | -- | |
24 | Replace the PCM. Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
25 |
Does the engine start and continue to run? | -- | ||
26 |
Are there any additional DTCs displayed? | -- | Go to Applicable DTC Table | |
27 | Use the scan tool in order to select Capture Info, Review Info. Are there any additional DTCs displayed that have not been diagnosed? | -- | Go to Applicable DTC Table | System OK |
Fuel Pump Electrical Circuit Diagnosis MFI
Go to full page mechanization drawing.
Cell 22: Fuel Controls
Circuit Description
The electrical circuit for the lift pump involves several main components:
| • | The oil pressure switch/sending unit that is threaded into a lubrication system passage. |
| • | A relay. |
| • | The fuel pump that is mounted under the vehicle on the frame rail. |
When the ignition switch is in the crank position, the lift pump circuit is completed through the relay contacts. During this time, oil pressure is building to the point of closing the contacts of the oil pressure switch. A minimum of 28 kPa (4 psi) is required to close the oil pressure switch contacts.
When the ignition switch is returned to the RUN position, the oil pressure of the running engine maintains electrical power to the lift pump. For diagnosis of the lift pump electrical circuit, refer to Fuel Pump Relay Circuit Diagnosis .
Diagnostic Aids
Possible long crank times or a poor performance problem will exist.
Test Description
The number(s) below refer to step number(s) on the Diagnostic Table.
-
Checks for proper operation of the fuel pump.
-
Check the battery feed circuit to the fuel pump relay.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Apply a 12 volt fused jumper to the fuel pump test terminal. Does the fuel pump operate? | -- | |||
Is the test light ON? | -- | |||
3 | Connect a test light between the fuel pump relay battery feed circuit and the circuit at the relay center. Is the test light ON? | -- | ||
4 |
Is the test light ON? | -- | ||
5 |
Was a problem found? | -- | ||
6 |
Is the test light ON? | -- | ||
7 | With a test light connected to B+ probe the fuel pump ground terminal at the fuel pump harness connector. Is the test light ON? | -- | ||
8 | Repair the open in the battery feed circuit to the fuel pump relay harness connector terminal in the relay center. Is the action complete? | -- | -- | |
9 | Repair the open in the fuel pump relay ground circuit. Is the action complete? | -- | -- | |
10 |
Was a problem found? | -- | -- | |
11 | Replace the fuel pump relay. Refer to Fuel Injection Line Replacement . Is the action complete? | -- | -- | |
12 | Replace the fuel pump. Refer to Fuel Lift Pump Replacement . Is the action complete? | -- | -- | |
13 | Repair the open between the fuel pump test terminal and the fuel pump feed circuit at the fuel pump harness connector. Is the action complete? | -- | -- | |
14 | Repair the open in the fuel pump harness ground circuit. Is the action complete? | -- | -- | |
15 | Start and idle vehicle. Is the fuel pump operating? | -- | System OK | -- |
