Fuel Pump Electrical Circuit Diagnosis VIN K
Circuit Description
When the ignition switch is first turned ON, the PCM energizes the fuel pump relay which applies power to the 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 output controls function.
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through the wire insulation or a wire broken insideof 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
Number(s) below refer to the Step number(s) on the Diagnostic Table:
-
Verifies that the fuel pump high circuit is OK between the fuel pump relay and the fuel pump, and that the fuel pump can deliver adequate pressure to the fuel rail.
-
Checks the battery positive voltage circuit to the fuel pump relay.
-
Ensures that the fuel pump relay control circuit and the PCM are capable of controlling the fuel pump relay. Using the scan tool to command the fuel pump allows only a 2 second time in the commanded state.
-
Checks the fuel pump control circuit for a short to ground.
-
Checks the fuel pump control circuit for an open.
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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.
-
Checks the fuel pump high circuit between the fuel pump relay and the fuel pump. Also checks the fuel pump low circuit.
-
Determines whether the problem is being caused by an open in the fuel pump high circuit or the fuel pump low circuit.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Is fuel pressure indicated at the specified value? | 333-376 kPa (48-55 psi) | |||
Is the test light ON? | -- | |||
Does the test light turn ON when the fuel pump is commanded ON? | -- | |||
Is the test light ON? | -- | |||
Was a problem found? | -- | |||
7 |
Was a problem found? | -- | ||
8 |
Was a problem found? | -- | ||
9 | Probe the battery positive voltage circuit at the fuel pump relay connector with a test light to ground. Is the test light ON? | -- | ||
Remove the fuel filler cap and listen for the fuel pump running. Is the fuel pump running? | -- | Go to Fuel System Pressure Test (VIN K) | ||
Is the test light ON? | -- | |||
Probe the fuel pump high circuit at the modular fuel sender harness connector with a test light to chassis ground. Is the test light ON? | -- | |||
13 | Locate and repair open in the fuel pump high circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |
14 | Locate and repair open in the fuel pump low circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |
15 | Locate and repair short to ground in the fuel pump relay control circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |
16 | Locate and repair open in the battery positive voltage circuit to the fuel pump relay. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |
17 | Locate and repair open in ground circuit to the fuel pump relay. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |
18 | Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement . Is action complete? | -- | -- | |
19 | Replace the fuel pump. Refer to Fuel Sender Assembly Service . Is action complete? | -- | -- | |
Replace the PCM Important: : The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
21 |
Is fuel pressure indicated at the specified value? | 333-376 kPa (48-55 psi) | System OK |
Fuel Pump Electrical Circuit Diagnosis VIN 1
Circuit Description
When the Ignition switch is first turned ON, the PCM energizes the fuel pump relay which applies power to the fuel pump through the high speed circuit (controlled by the fuel pump speed control relay). 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 turn ON by using the scan tool output controls function.
The PCM alters fuel pump speed by energizing the fuel pump speed control relay Under normal conditions, the fuel pump control speed control relay is energized (normal fuel pump speed). The applied voltage to the fuel pump is controlled by a resistor assembly. When higher fuel volume is required due to increased engine load (MAP sensor value over 90 kPa). the PCM de-energizes the fuel pump speed control relay circuit. The increased voltage to the in-tank fuel pump allows a higher volume of fuel to be delivered to the fuel rail. The PCM also compensates for low system voltage by energizing the fuel pump speed control relay.
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
Number(s) below refer to the Step number(s) on the Diagnostic Chart:
-
The fuel pump primes the fuel rail/injectors using the high speed circuit. This check ensures proper fuel pressure for the vehicle to start.
-
Once the engine starts the PCM commands the fuel pump to operate at normal speed (slightly lower pressure to the fuel rail/injectors). This check ensures proper operation of the fuel pump normal speed circuit.
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Checks for a short to ground in the feed circuit to the fuel pump relay.
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Checks for a short to ground in the feed circuit between the fuel pump and fuel pump speed control relay.
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Checks for a short to ground in the feed circuit or speed control resistor circuit to the fuel pump.
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Ensures that the fuel pump relay driver 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.
-
Checks the continuity of the speed control and fuel pump feed harness/splices.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic System Check performed? | -- | ||||||
2 | Is DTC P1643 set? | -- | ||||||
3 |
Important: Leave the gauge installed for the entire diagnostic. Is proper fuel pressure indicated? | 333-376 kPa (48-55 psi) | ||||||
4 |
Important: If the engine cranks but will not run, continue with the Engine Cranks but Does Not Start diagnostic table.
Is proper fuel pressure indicated? | 333-376 kPa (48-55 psi) | No trouble found | |||||
5 | Check for a blown fuel pump fuse. Is the fuse blown? | -- | ||||||
6 |
Is the test light ON? | -- | ||||||
7 | Locate and repair short to ground in the B+ feed to the fuel pump relay . Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||
8 |
Is the test light ON? | -- | ||||||
9 | Locate and repair the short between the B+ feed to cavities 86 and 30 in the fuel pump control relay and the following locations:
Is action complete? | -- | -- | |||||
10 |
Is the test light ON? | -- | ||||||
11 | Locate and repair short between the following circuits and chassis/fuel pump ground:
Is action complete? | -- | -- | |||||
12 |
Did the fuse blow? | |||||||
13 |
Is proper fuel pressure indicated? | |||||||
14 |
Is the test light ON? | |||||||
15 |
Is the test light ON? | |||||||
16 |
Was a problem found? | |||||||
17 | Locate and repair open fuel pump relay ground circuit . Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||
18 |
Is the test light ON? | -- | ||||||
19 |
Is proper fuel pressure indicated? | |||||||
20 | Locate and repair open in the B+ feed to the fuel pump relay . Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||
21 |
Was a problem found? | |||||||
22 |
Was a problem found? | |||||||
23 | Check for an open fuel pump speed control resistor. Was a problem found? | |||||||
24 |
Is the test light ON? | |||||||
25 |
Was a problem found? | -- | ||||||
26 | Connect the test light between terminal C in the fuel pump connector and chassis ground. Is the test light ON? | |||||||
27 | Locate and repair open or poor terminal connection in the fuel pump ground circuit. Is action complete? | -- | ||||||
28 | Locate and repair open or poor terminal connections in the following circuits:
Is action complete? | -- | ||||||
29 | Replace the fuel pump speed control resistor. Is action complete? | -- | ||||||
30 | Replace the fuel pump. Refer to Fuel Sender Assembly Service Is action complete? | -- | ||||||
31 | Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement Is action complete? | -- | ||||||
32 | Replace the fuel pump speed control relay Is action complete? | -- | ||||||
33 | Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | |||||
34 |
Is proper fuel pressure indicated? | 333-376 kPa (48-55 psi) | ||||||
35 |
Does the fuel pressure increase slightly when high fuel pump speed is selected? | -- | System OK |
