Circuit Description
When the ignition is turned ON, the powertrain control module (PCM) turns ON the in-tank fuel pump. The pump will remain ON as long as the PCM is receiving ignition reference pulses from the electronic ignition control module (ICM). If there are no reference pulses, the PCM will shut OFF the fuel pump about 2-3 seconds after the ignition is turned ON, about 10 seconds after the reference pulses stop.
The fuel pump delivers fuel to the fuel rail and fuel injectors, then to the fuel pressure regulator, where the system pressure is controlled to 283-324 kPa (41-47 psi) with no manifold vacuum or 214-303 kPa (31-44 psi) at idle. Excess fuel is then returned to the fuel tank.
Improper Fuel System pressure will result in one or all of the following symptoms:
| • | Cranks But Will Not Run |
| • | DTC P0171 |
| • | DTC P0172 |
| • | DTC P1171 |
| • | DTC P0300 |
| • | Cuts out, may feel like an ignition problem |
| • | Poor fuel economy, loss of power |
| • | Hesitation |
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for a poor connection or damaged harness. Inspect the PCM harness and connectors for the following items:
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wire connections |
| • | Damaged harnesses |
Test Description
The number(s) below refer(s) to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool, if applicable. This creates an electronic copy of the data captured when this DTC set. The scan tool stores this data for later reference.
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If the no start condition was due to an open fuse, locate and repair any shorts that may have caused the fuse to open before the replacement.
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This step determines if the PCM can control the fuel pump. The PCM should energize the fuel pump relay and turn ON the fuel pump when commanded by the scan tool. If the engine is not cranking or running, the PCM should de-energize the relay and turn OFF the fuel pump after 2-3 seconds.
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Connecting a fused jumper wire between the fuel pump feed terminal and the fuel pump relay ignition feed terminal verifies that the following circuits are all OK.
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This step checks for an open in the fuel pump ground circuit.
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Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communications System (ITCS) information for PCM programming and Crankshaft Position System Variation Learn for the Crankshaft Position System Variation Learn Procedure.
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This test will determine if a short to ground on the fuel pump feed circuit or the fuel injector feed circuit caused the fuse to open. Be sure to disconnect the fuel pump harness before the test in order to prevent a mis-diagnosis.
| • | Fuel pump relay ignition feed circuit |
| • | Fuel pump feed circuit |
| • | Fuel pump |
| • | Fuel ground |
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
Inspect the Fuel Pump Relay Ignition Feed fuse. Is the fuse OK? | -- | |||||||||
Does the in-tank fuel pump run when the fuel pump relay is commanded ON? | -- | Go to Fuel System Diagnosis | ||||||||
Does the fuel pump run? | -- | |||||||||
5 |
Does the test light illuminate? | -- | ||||||||
6 |
Is the test light ON? | -- | ||||||||
Is the test light ON? | -- | |||||||||
8 |
Was a repair necessary? | -- | ||||||||
9 |
Does the test light illuminate? | -- | ||||||||
10 | Repair the open in the ignition feed circuit for the fuel pump relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
11 | Replace the fuel pump relay. Refer to the Fuel Pump Relay Replacement . Is the action complete? | -- | -- | |||||||
12 | Repair the open in the ground circuit to the fuel pump relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
13 |
Was a repair necessary? | -- | ||||||||
14 |
Does the test light illuminate? | -- | ||||||||
15 | Repair the open in the fuel pump feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
Is the action complete? | -- | -- | ||||||||
17 |
Was a repair necessary? | -- | ||||||||
18 | Repair the open in the fuel pump ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
19 | Replace the fuel pump. Refer to the Fuel Sender Assembly Replacement . Is the action complete? | -- | -- | |||||||
Does the test light illuminate? | -- | |||||||||
21 | Repair the short to ground in the following circuits. Refer to Wiring Repairs in Wiring Systems.
Is the action complete? | -- | -- | |||||||
22 |
Does the test light illuminate? | -- | ||||||||
23 | Repair the short to ground in the fuel pump relay ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
24 |
Was a repair necessary? | -- | ||||||||
25 |
Does the engine start and continue to run? | -- | ||||||||
26 |
Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK |
