Fuel System Diagnosis (LDD)
Diagnostic Instructions
Circuit/System Description
When the ignition is turned ON, the engine control module (ECM)
supplies power to the in-tank fuel pump, by energizing the fuel
pump relay. The in-tank fuel pump remains ON as long as the engine
is cranking or running and the ECM receives crankshaft reference
pulses. If there are no reference pulses, the ECM turns the in-tank
fuel pump OFF, 2 s after the ignition switch is turned ON or 2 s
after the engine stops running. The electric fuel pump is
incorporated into the modular fuel pump and sender assembly and is
located inside the fuel tank. The fuel pump supplies fuel through a
fuel filter, also located in the modular fuel pump and sender
assembly, through the fuel feed pipes, to the fuel rail assembly.
The fuel pump provides fuel at a pressure above the pressure needed
by the fuel injectors. The fuel pressure regulator, located in the
modular fuel pump and sender assembly, keeps the fuel available to
the fuel injectors at a regulated pressure. When the fuel pressure
rises above the pressure regulator calibration, the pressure is
relieved, with excess fuel exhausted into the modular fuel pump and
sender assembly reservoir.
Reference Information
Description and Operation
Fuel System Description
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Special Tools
• |
CH 48027
Digital Pressure Gauge |
• |
EN 37287 Fuel
Line Shut-Off Adapters |
For equivalent regional tools, refer to
Special Tools .
Circuit/System Verification
Note:
• |
Inspect the fuel
system for damage or external leaks before proceeding. |
• |
Verify that an
adequate amount of fuel is in the fuel tank before
proceeding. |
• |
The fuel pump
relay may need to be commanded ON a few times in order to obtain
the highest possible fuel pressure. |
1. |
Ignition ON, command the KR23A
Fuel Pump Relay ON with a scan tool. You should hear the G12 Fuel
Pump turn ON and OFF. |
2. |
Ignition OFF, all accessories
OFF, install the CH 48027 digital pressure gauge
. |
3. |
Ignition ON, command the KR23A
Fuel Pump Relay ON with a scan tool. Verify the fuel pressure is
between 365-414 kPa (53-60 PSI) and remains steady for 5 m.
|
Circuit/System Testing
|
Note:
• |
The KR23A Fuel
Pump Relay may need to be commanded ON a few times in order to
obtain the highest possible fuel pressure. |
• |
Do not start the
engine. |
|
1. |
Ignition ON, engine OFF,
command the KR23A Fuel Pump Relay ON with a scan tool and observe
the fuel pressure gauge while the G12 Fuel Pump is operating.
Verify the fuel pressure is between 345-414 kPa (50-60 PSI).
|
⇒ |
If the fuel pressure is greater than the specified
range, replace the G12 Fuel Pump. |
⇒ |
If the fuel pressure is less than the specified
range, test, inspect, and repair the items listed below. If all
items test normal, replace the G12 Fuel Pump. |
|
• |
Restricted fuel feed
pipe |
|
• |
Restricted or clogged
strainer |
|
• |
Restricted or plugged fuel
filter |
|
Note: The fuel pressure may
vary slightly when the G12 Fuel Pump stops operating. After the G12
Fuel Pump stops operating, the fuel pressure should stabilize and
remain constant.
|
|
|
|
|
• |
Inspect the G12 Fuel Pump
harness connectors and the ground circuits of the fuel pump for
poor connections. |
2. |
Verify the fuel pressure does
not decrease greater than 34 kPa (5 PSI) in 1 min. |
⇒ |
If the fuel pressure decreases more than the
specified value, perform the following procedure: |
|
2.1 |
Ignition OFF, relieve fuel
pressure. |
|
2.2 |
Install the EN 37287
fuel line shut-off adaptors between the fuel feed pipe and
the fuel rail. |
|
2.3 |
Open the valve on the EN
37287 fuel line shut-off adaptors . |
|
2.4 |
Ignition ON, command the fuel
pump relay ON with a scan tool and bleed the air from the digital
pressure gauge. |
|
2.5 |
Close the valve on the EN
37287 fuel line shut-off adaptors . |
|
2.6 |
Verify the fuel pressure does
not decrease greater than 34 kPa (5 PSI) in 1 minute. |
⇒ |
If the fuel pressure decreases more than 34 kPa (5 PSI) within
the specified time, locate and replace the leaking fuel
injector(s). If the fuel pressure does not decrease more than 34
kPa (5 PSI) within the specified time, replace the G12 Fuel
Pump. |
3. |
Relieve the fuel pressure to
69 kPa (10 PSI). Verify that the fuel pressure does not decrease
more than 14 kPa (2 PSI) in 5 min. |
⇒ |
If the fuel pressure decreases more than the
specified value, replace the G12 Fuel Pump. |
4. |
Remove the EN 37287
fuel line shut-off adaptors and CH 48027
digital pressure gauge . |
5. |
Operate the vehicle within the
conditions of the customers concern while monitoring fuel related
parameters with a scan tool. The scan tool parameters should not
indicate a lean condition. |
⇒ |
If the scan tool parameters indicate a lean
condition, test for a restricted fuel feed pipe, restricted fuel
filter, or poor connections at the harness connectors and ground
circuits of the fuel pump. If all test normal, replace the fuel
pump. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|