Fuel Pump Electrical Circuit Diagnosis EFI
Go to Engine Controls Schematic
Cell 23: Fuel Controls 1 -- Fuel Lift Pump and Relay
Circuit Description
When the key is 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.
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.
-
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 function to save the Freeze Frame and the Failure records for reference. The control module's data is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
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 lamp ON? | -- | |||
6 | Connect an J 35616-200 unpowered test lamp between the fuel pump relay battery feed circuit harness connector and ground. Is the test lamp ON? | -- | ||
7 |
Is the test lamp ON during glow plug cycle and then OFF? | -- | ||
8 | Check for a poor connection at the fuel pump relay control connector terminal. Refer to Wiring Repairs in Wiring Systems. Did you perform a repair? | -- | ||
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 lamp ON? | -- | ||
12 |
Is the test lamp ON? | -- | ||
13 | With an J 35616-200 unpowered test lamp connected to B+ probe the fuel pump ground terminal (vehicle side) of the chassis harness fuel pump connector. Is the test lamp ON? | -- | ||
14 | Repair the open in the battery feed circuit to the fuel pump relay harness connector terminal. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | --
| |
15 | Repair the open in the fuel pump relay ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | --
| |
16 |
Did you perform a repair? | -- | ||
17 | Check the oil pressure switch harness connector terminals for a poor connection. Refer to Wiring Repairs in Wiring Ssytems. Did you perforn a repair? | -- | ||
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. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
21 | Repair the open in the fuel pump harness ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
22 | Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
23 | Repair the connection as necessary. Refer to Wiring Repairs in Wiring Systems. 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 | Operate the vehicle within the conditions that the system was noted. Does the system operate properly? | -- |
Fuel Pump Electrical Circuit Diagnosis MFI
Go to Engine Controls Schematic
Cell 22: Fuel Controls 1 -- Fuel Pump Control
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 lamo ON? | -- | |||
3 | Connect an J 35616-200 unpowered test lamp between the fuel pump relay battery feed circuit and the circuit at the relay center. Is the test lamp ON? | -- | ||
4 |
Is the test lamp ON? | -- | ||
5 |
Did you perform a repair? | -- | ||
6 |
Is the test lamp ON? | -- | ||
7 | With an J 35616-200 unpowered test lamp connected to B+ probe the fuel pump ground terminal at the fuel pump harness connector. Is the test lamp 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. Refer to Wiring Repairs. Is the action complete? | -- | -- | |
10 |
Did you perform a repair? | -- | -- | |
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. Refer to Wiring Repairs. Is the action complete? | -- | -- | |
14 | Repair the open in the fuel pump harness ground circuit. Refer to Wiring Repairs. Is the action complete? | -- | -- | |
15 | Start and idle vehicle. Is the fuel pump operating? | -- | System OK | -- |
