Fuel Pump Electrical Circuit Diagnosis VIN K
Refer to Engine Controls Schematics
Fuel Pump and Relay, L36
.
Circuit Description
When the ignition switch is first turned ON, the powertrain control module (PCM) energizes the fuel pump relay which applies battery positive voltage to the in-tank fuel pump. The fuel pump relay will remain ON as long as the engine is running or cranking and the PCM is receiving reference pulses. If no reference pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped.
The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator controls fuel pressure by allowing excess fuel to be returned to the fuel tank. With the engine stopped, the fuel pump can be turned ON by using the scan tool device controls function.
Diagnostic Aids
Inspect for the following:
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
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Command both the ON and OFF states. Repeat the commands as necessary.
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This step determines if the condition is located on the coil side or the switch side of the circuit.
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This step verifies that the powertrain control module (PCM) is providing voltage to the fuel pump relay.
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This step tests for an open in the ground circuit to the fuel pump relay.
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This step determines if a voltage is constantly being applied to the fuel pump relay.
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This step tests for a grounded fuel pump supply circuit between the fuel pump and the fuel pump fuse.
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This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage between the fuse and the fuel pump for an intermittent condition.
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This step jumps the fuel pump relay in order to bypass the fuel pump relay and activate the fuel pump.
-
This step tests the fuel pump supply circuit between the fuel pump and the fuel pump relay for an open or high resistance.
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This step tests the fuel pump ground circuit for an open or high resistance.
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you Perform the Powertrain On-Board Diagnostic (OBD) System Check? | ||
Does the fuel pump turn ON and OFF? | Go to Intermittent Conditions | ||
With a scan tool, command the fuel pump relay ON and OFF. Do you hear a click from the relay when you command the fuel pump ON and OFF? | |||
Does the test lamp turn ON and OFF? | |||
Does the test lamp turn ON and OFF? | |||
Does the test lamp remain illuminated with each command? | |||
7 |
Did you find and correct the condition? | ||
8 |
Did you find and correct the condition? | ||
9 | Turn ON the ignition, with the engine OFF. Does the fuel pump operate continuously? | ||
10 |
Does the fuel pump operate continuously? | ||
11 | Is the fuel pump fuse open? | ||
Did you find and correct the condition? | |||
Is the fuel pump fuse open? | Go to Intermittent Conditions | ||
14 |
Does the test lamp illuminate? | ||
Connect a 20 amp fused jumper wire between the switch supply circuit of the fuel pump relay and the pump supply circuit of the fuel pump relay. Does the fuel pump operate? | |||
Did you find and correct the condition? | |||
|
Important: Visually/physically inspect the ground circuit for being tight, corrosion on terminals or damage to the wiring harness. Test the ground circuit of the fuel pump for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | |||
18 | Inspect for poor connections at the fuel pump. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | ||
19 | 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? | ||
20 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | ||
21 | Repair the supply voltage circuit of the fuel pump for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | |
22 | Repair the ground circuit of the fuel pump relay for an open. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | |
23 | Repair the relay switch supply circuit of the fuel pump relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | |
24 |
Important: Inspect for poor connections at the fuel pump, within the fuel tank, before replacing the fuel pump.
Did you complete the replacement? | -- | |
25 | Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement . Did you complete the replacement? | -- | |
26 |
Important: The replacement PCM must be programed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . | -- | |
27 | Operate the system in order to verify the repair. Did you correct the condition? | System OK |
Fuel Pump Electrical Circuit Diagnosis VIN 1
Refer to Engine Controls Schematics
Fuel Pump Control, L67
.
Circuit Description
When the ignition switch is first turned ON, the powertrain control module (PCM) energizes the fuel pump relay which applies battery positive voltage to the fuel pump control module. The fuel pump relay will remain ON as long as the engine is running or cranking and the PCM is receiving reference pulses. If no reference pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped. The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator controls fuel pressure by allowing excess fuel to be returned to the fuel tank. With the engine stopped, the fuel pump can be turned ON by using the scan tool output controls function.
The PCM alters fuel pump speed by varying the duty cycle on the fuel pump speed control PWM circuit to the fuel pump control module. Under normal conditions, the fuel pump speed control PWM circuit duty cycle is set at 33 percent . When higher fuel volume is required due to increased engine load (MAP sensor value over 90 kPa), the PCM switches the fuel pump speed control PWM circuit duty cycle to 100 percent . At the higher duty cycle, the fuel pump control module increases the voltage to the in-tank fuel pump, allowing a higher volume of fuel to be delivered to the fuel rail. The PCM also compensates for low system voltage by switching the fuel pump control circuit PWM duty cycle to 100 percent .
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through the wire insulation or a wire broken inside of the insulation.
Check for a poor connection or a 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 numbers below refer to the step numbers on the diagnostic table.
-
Fuel pressures within the specified range are sufficient for the vehicle to start. If directed to this table from the Engine Cranks But Will Not Run table, continue diagnosis with Engine Cranks But Will Not Run.
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Ensures that the fuel pump speed control PWM circuit and the PCM are capable of controlling fuel pump speed.
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Verifies that the fuel pump feed and ground circuits are OK between the fuel pump control module and the fuel pump, and that the fuel pump can deliver adequate pressure to the fuel rail.
-
Checks the feed circuit to the fuel pump control module.
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Ensures that the fuel pump speed control PWM circuit is not shorted to ground.
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Checks the ignition feed circuit to the fuel pump relay contacts.
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Checks the ground circuit for the fuel pump relay coil.
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Ensures that the fuel pump relay control circuit is OK and that the PCM is capable of controlling the fuel pump relay. Using the scan tool to command the fuel pump relay allows only a 2 second ON time.
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Checks the fuel pump relay control circuit for a short to ground.
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If the fuel pump is operating but incorrect pressure is observed, the fuel pump wiring is OK and the Fuel System Pressure Test should be used for diagnosis.
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Determines whether the problem is being caused by an open in the fuel pump feed circuit or the fuel pump ground circuit.
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Ensures that the fuel pump speed control PWM circuit is OK and that the PCM can control the fuel pump speed control circuit. Using the scan tool to command the FP Speed allows only a 2 second time in the commanded state.
-
This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On Board Diagnostic (OBD) System Check performed? | -- | ||||||
2 | Is DTC P0230 or any other DTCs set? | -- | ||||||
Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete. Is the fuel pressure within the specified range? | 333-376 kPa (48-55 psi) | |||||||
|
Important:: If the engine cranks but will not run, continue with Engine Cranks but Does Not Run .
Does the fuel pressure increase slightly when high fuel pump speed is selected? | -- | System OK | ||||||
Is the fuel pressure within the specified range? | 333-376 kPa (48-55 psi) | |||||||
Does the test lamp illuminate? | -- | |||||||
7 | Probe terminal 4 (fuel pump control module ground circuit) with a test lamp connected to B+. Does the test lamp illuminate? | -- | ||||||
Does the test lamp illuminate? | -- | |||||||
9 | Locate and repair a short to ground in the fuel pump speed control PWM circuit. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||
10 |
Is the voltage more than the specified value while the fuel pump relay is commanded ON? | 8 V | ||||||
11 |
Does the test lamp illuminate while the fuel pump relay is commanded ON? | -- | ||||||
12 |
Was a problem found? | -- | Go to Diagnostic Aids | |||||
Does the test lamp illuminate? | -- | |||||||
Connect the test lamp between the fuel pump relay feed circuit terminal 87 and the fuel pump relay ground circuit terminal 86. Does the test lamp illuminate? | -- | |||||||
Does the test lamp illuminate with the fuel pump relay commanded ON? | -- | |||||||
16 |
Does the test lamp illuminate? | -- | ||||||
17 |
Is the action complete? | -- | ||||||
18 | Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement . Is the action complete? | -- | -- | |||||
19 | Locate and repair an open in the fuel pump relay feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
20 | Locate and repair an open in the fuel pump relay ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
Does the test lamp illuminate? | -- | |||||||
22 | Locate and repair a short to ground in the fuel pump relay control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |||||
23 |
Was a problem found? | -- | ||||||
24 | Locate and repair an open in fuel pump control module feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
25 | Locate and repair an open in the fuel pump control module ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
Remove the fuel filler cap and listen for the fuel pump running. Is the fuel pump running? | -- | |||||||
27 |
Does the test lamp illuminate? | -- | ||||||
Probe the fuel pump feed circuit at the modular fuel sender harness connector with a test lamp connected to chassis ground. Does the test lamp illuminate? | -- | |||||||
29 | Locate and repair an open in the fuel pump feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |||||
30 | Locate and repair an open in the fuel pump ground circuit. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||
Is the test lamp illuminated with normal selected and OFF with high selected? | -- | |||||||
32 |
Does the voltage approximately equal the specified values? | 8 V B+ | ||||||
33 |
Was a problem found? | -- | ||||||
34 |
Was a problem found? | -- | ||||||
35 | Replace the fuel pump control module. Refer to Fuel Pump Control Module Replacement . Is the action complete? | -- | -- | |||||
36 |
Was a problem found? | -- | ||||||
37 | Replace the fuel pump. Refer to Fuel Sender Assembly Replacement . Is the action complete? | -- | -- | |||||
|
Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||||||
39 |
Is the fuel pressure within the specified range? | 333-376 kPa (48-55 psi) | ||||||
40 |
Does the fuel pressure increase slightly when the fuel pump high speed is selected? | -- | System OK |
