Circuit/System Description
Ignition voltage is supplied to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit.
This Engine Cranks but Does Not Run is an organized approach to identify a condition which causes the engine to crank but not start. This diagnostic directs the technician to the appropriate system diagnosis.
This diagnostic assumes the system voltage levels are adequate for starter motor operation. Refer to Battery Inspection/Test and Engine Cranks Slowly . Fuel level and fuel quality should be determined for correct diagnosis.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 3: This step determines if the condition is located on the coil side or the switch side of the circuit.
- 4: This step verifies that the PCM is providing voltage to the fuel pump relay.
- 5: This step tests for an open in the ground circuit to the fuel pump relay.
- 6: This step determines if a voltage is constantly being applied to the fuel pump relay.
- 13: This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Engine Controls Schematics (LX9) Connector End View Reference: Engine Controls Component Views or Powertrain Control Module (PCM) Connector End Views | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 2 | Turn ON the ignition, with the engine OFF. Command the fuel pump relay ON and OFF with a scan tool. Does the fuel pump turn ON and OFF? | Go to Diagnostic Aids | Go to Step 3 |
| 3 | Command the fuel pump relay ON and OFF with a scan tool. Do you hear a click when you command the fuel pump relay ON and OFF? | Go to Step 9 | Go to Step 4 |
| 4 | Turn OFF the ignition. Disconnect the fuel pump relay. Turn ON the ignition, with the engine OFF. Probe the control circuit of the fuel pump relay with a test lamp that is connected to a good ground. Command the fuel pump relay ON and OFF with a scan tool. Does the test lamp turn ON and OFF? | Go to Step 5 | Go to Step 6 |
| 5 | Connect a test lamp between the control circuit of the fuel pump relay and the ground circuit of the fuel pump relay. Command the fuel pump relay ON and OFF with a scan tool. Does the test lamp turn ON and OFF? | Go to Step 19 | Go to Step 22 |
| 6 | Does the test lamp remain illuminated with each command? | Go to Step 7 | Go to Step 8 |
| 7 | Test the control circuit of the fuel pump relay for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 26 |
| 8 | Test the control circuit of the fuel pump relay for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 20 |
| 9 | Turn ON the ignition, with the engine OFF. Does the fuel pump operate continuously? | Go to Step 10 | Go to Step 11 |
| 10 | Turn OFF the ignition. Disconnect the fuel pump relay. Turn ON the ignition, with the engine OFF. Does the fuel pump operate continuously? | Go to Step 21 | Go to Step 25 |
| 11 | Is the fuel pump fuse open? | Go to Step 12 | Go to Step 14 |
| 12 | Test the supply voltage circuit of the fuel pump for a grounded circuit between the fuel pump fuse and the fuel pump. Refer to Circuit Testing and Wiring Repairs . Replace the fuel pump fuse if necessary. Did you find and correct the condition? | Go to Step 27 | Go to Step 13 |
| 13 | Install all disconnected electrical components. Install a new fuel pump fuse. Command the fuel pump relay ON with a scan tool. Inspect the fuel pump fuse. Is the fuel pump fuse open? | Go to Step 24 | Go to Testing for Intermittent Conditions and Poor Connections |
| 14 | Turn OFF the ignition. Disconnect the fuel pump relay. Turn ON the ignition, with the engine OFF. Probe the battery voltage circuit of the fuel pump relay switch with a test lamp that is connected to a good ground. Does the test lamp illuminate? | Go to Step 15 | Go to Step 23 |
| 15 | Connect a 15-amp fused jumper wire between the battery voltage circuit of the fuel pump relay switch and the supply voltage circuit of the fuel pump. Does the fuel pump operate? | Go to Step 19 | Go to Step 16 |
| 16 | Test the supply voltage circuit of the fuel pump for an open or high resistance between the fuel pump relay and the fuel pump. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 17 |
| 17 | IMPORTANT: 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 .Did you find and correct the condition? | Go to Step 27 | Go to Step 18 |
| 18 | Inspect for poor connections at the fuel pump. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 24 |
| 19 | Inspect for poor connections at the fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 25 |
| 20 | Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 26 |
| 21 | Repair the supply voltage circuit of the fuel pump for a short to voltage. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 27 | |
| 22 | Repair the open fuel pump relay ground circuit. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 27 | |
| 23 | Repair the battery voltage circuit of the fuel pump relay switch. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 27 | |
| 24 | IMPORTANT: Inspect for poor connections at the fuel pump, within the fuel tank, before replacing the fuel pump. Replace the fuel pump. Refer to Fuel Sender Assembly Replacement (Short Wheel Base) or Fuel Sender Assembly Replacement (Long Wheel Base) . Replace the fuel pump fuse if necessary. Did you complete the replacement? | Go to Step 27 | |
| 25 | Replace the fuel pump relay. Did you complete the replacement? | Go to Step 27 | |
| 26 | Replace the PCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 27 | |
| 27 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK |
| IMPORTANT |
|---|
| Inspect the ground circuit for being tight, corrosion on terminals or damage to the wiring harness. |
| IMPORTANT |
|---|
| Inspect for poor connections at the fuel pump, within the fuel tank, before replacing the fuel pump. |
Fuel Pump Electrical Circuit Diagnosis
System Description
The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.
The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the primary fuel tank module, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
An electric turbine style fuel pump attaches to the primary fuel tank module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, past the fuel pressure regulator and through the fuel feed pipe to the fuel injection system. The fuel pressure regulator has a T-joint that diverts the needed fuel to the fuel rail with the unused fuel dropping back into the reservoir of the primary fuel tank module. The primary fuel tank module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
The primary fuel tank module also contains a primary jet pump and a secondary jet pump. Fuel pump flow loss, caused by vapor expulsion in the pump inlet chamber, is diverted to the primary jet pump and the secondary jet pump through a restrictive orifice located on the pump cover. The primary jet pump fills the reservoir of the primary fuel tank module. The secondary jet pump creates a venturi action which causes the fuel to be drawn from the secondary side of the fuel tank, through the fuel transfer pipe, to the primary side of the fuel tank.
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |
| 2 | IMPORTANT: Inspect the fuel system for damage or external leaks before proceeding with this diagnostic. Turn ON the ignition, with the engine OFF. Command the fuel pump relay ON with a scan tool. Does the fuel pump operate? | Go to Step 3 | Go to Fuel Pump Electrical Circuit Diagnosis | |
| 3 | IMPORTANT: Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic. Turn OFF the ignition. Turn OFF all accessories. Install the SA9127E Gage Bar Set with the Fuel Pressure Adapter and the Drain Hose. Refer to Fuel Pressure Gage Installation and Removal . Turn ON the ignition, with the engine OFF. IMPORTANT: DO NOT start the engine. Command the fuel pump relay ON with a scan tool. Observe the fuel pressure gage with the fuel pump commanded ON. Is the fuel pressure within the specified range? | 345-414 kPa (50-60 psi) | Go to Step 4 | Go to Step 7 |
| 4 | IMPORTANT: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. Monitor the fuel pressure gage for 5 minutes.Does the fuel pressure decrease by more than the specified value? | 55 kPa (8 psi) | Go to Step 6 | Go to Step 5 |
| 5 | Operate the vehicle within the conditions to reproduce the original symptoms. Monitor the O2 and the Fuel Trim parameters with a scan tool. Do the scan tool parameters indicate a lean condition? | Go to Step 8 | Go to Symptoms - Engine Controls | |
| 6 | Turn OFF the ignition. Relieve the fuel pressure. Refer to Fuel Pressure Relief Procedure . Remove the fuel pressure gage from the fuel pressure test connection. Disconnect the chassis fuel hose from the engine compartment fuel pipe. Connect the fuel feed hose to the inlet side of SA9127E-7 Fuel Pressure/Flow Adapter using the J 43937 3/8-Inch Male Fuel Pressure Adapter Line. See Special Tools . Connect the return hose from the SA9127E-7 to the outlet side of SA9127E-7 . Place the other end of the return hose into the fuel filler pipe. Connect the fuel pressure gage to the SA9127E-7 . Close the valve on the SA9127E-7 . Turn ON the ignition, with the engine OFF. Command the fuel pump relay ON for a minimum of 10 seconds with a scan tool. Record the fuel pressure. Command the fuel pump relay OFF. Monitor the fuel pressure gage for 5 minutes. Does the fuel pressure decrease by more than the specified value? | 55 kPa (8 psi) | Go to Step 11 | Go to Step 9 |
| 7 | Is the fuel pressure more than the specified value? | 414 kPa (60 psi) | Go to Step 11 | Go to Step 8 |
| 8 | Turn OFF the ignition. Relieve the fuel pressure. Refer to Fuel Pressure Relief Procedure . Remove the fuel pressure gage from the fuel pressure test connection. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information. Disconnect the chassis fuel feed pipe at the fuel tank pipe. Connect the inlet side of SA9127E-7 to the fuel tank pipe using the J 43937 3/8-Inch Female Fuel Pressure Adapter Line. See Special Tools . Place the return hose from the SA9127E-7 into the fuel filler pipe. Connect the fuel pressure gage to the SA9127E-7 . Open the valve on the SA9127E-7 . Turn ON the ignition, with the engine OFF. Command the fuel pump relay ON for a minimum of 10 seconds with a scan tool. Is the fuel pressure more than the specified value? | 379 kPa (55 psi) | Go to Step 10 | Go to Step 11 |
| 9 | Turn OFF the ignition. Open the valve on the SA9127E-7 . Remove the SA9127E-7 . Connect the chassis fuel hose to the engine compartment fuel pipe. Raise the fuel rail, with the fuel line connected. Refer to Fuel Rail Assembly Replacement . Turn ON the ignition, with the engine OFF. Command the fuel pump relay ON with a scan tool. Locate and replace the leaking fuel injector. Refer to Fuel Injector Replacement . Did you complete the replacement? | Go to Step 12 | ||
| 10 | Replace the chassis fuel feed pipe. Refer to Fuel Hose/Pipes Replacement - Chassis . Did you complete the replacement? | Go to Step 12 | ||
| 11 | Replace the primary fuel tank module. Refer to Fuel Sender Assembly Replacement (Short Wheel Base) or Fuel Sender Assembly Replacement (Long Wheel Base) . Did you complete the replacement? | Go to Step 12 | ||
| 12 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3 |
| IMPORTANT |
|---|
| Inspect the fuel system for damage or external leaks before proceeding with this diagnostic. |
| IMPORTANT |
|---|
| Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic. |
| IMPORTANT |
|---|
| DO NOT start the engine. |
| IMPORTANT |
|---|
| The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. |
Fuel System Diagnosis
The numbers below refer to the step numbers on the diagnostic table.
- 3: This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
- 4: This step determines if all of the fuel injectors are within 3 ohms of each other. If the highest resistance value is within 3 ohms of the lowest resistance value, then all of the fuel injector coil windings are OK.
- 6: This step determines if the ignition 1 voltage circuit under the intake plenum is causing the concern.
- 8: This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| Schematic Reference: Engine Controls Schematics (LX9) Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module (PCM) Connector End Views | ||||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |
| 2 | Observe the engine coolant temperature (ECT) with a scan tool. Is the ECT value within the specified range? | 10-32°C (50-90°F) | Go to Step 3 | Go to Step 4 |
| 3 | Disconnect the fuel injector multi-way harness connector. Measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way connector with a DMM. Refer to Testing for Continuity in Wiring Systems. Do any of the fuel injectors display a resistance outside the specified range? | 11-14 ohms | Go to Step 5 | Go to Diagnostic Aids |
| 4 | Disconnect the fuel injector multi-way connector. Measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way connector with a DMM. Refer to Testing for Continuity in Wiring Systems. Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to or less than, the specified value? | 3 ohms | Go to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 | Go to Step 8 |
| 5 | Remove the upper intake manifold. Refer to Intake Manifold Removal - Upper in Engine Mechanical. Did you complete the action? | Go to Step 6 | ||
| 6 | Measure the resistance of the ignition 1 voltage circuit between the multi-way connector and the affected fuel injector connector, with a DMM. Is the resistance more than the specified value? | 5 ohms | Go to Step 7 | Go to Step 9 |
| 7 | Repair the open or high resistance in the ignition 1 voltage circuit. Did you complete the repair? | Go to Step 11 | ||
| 8 | Add all of the fuel injector resistance values, to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors, to obtain an average resistance value. Subtract the lowest and the highest individual fuel injector resistance values from the average resistance value. Replace the fuel injector that displays the greatest resistance difference, above or below the average. Refer to Fuel Injector Replacement . Did you complete the replacement? | Go to Step 11 | ||
| 9 | Test for an intermittent and for a poor connection at the affected fuel injector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 | |
| 10 | Replace any fuel injectors that are out of the specified range. Refer to Fuel Injector Replacement . Did you complete the replacement? | 11-14 ohms | Go to Step 11 | |
| 11 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 | |
Fuel Injector Coil Test
Scheme 143
| Callout | Component Name |
|---|---|
| 1 | First Fuel Pressure Gage Reading |
| 2 | Second Fuel Pressure Gage Reading |
The scan tool is first used to energize the fuel pump relay. The fuel injector tester is then used to pulse each injector for a precise amount of time, allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.
| Cylinder | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| 1st Reading | 379 kPa (55 psi) | 379 kPa (55 psi) | 379 kPa (55 psi) | 379 kPa (55 psi) |
| 2nd Reading | 280 kPa (41 psi) | 310 kPa (45 psi) | 340 kPa (49 psi) | 317 kPa (46 psi) |
| Amount of Drop | 99 kPa (14 psi) | 69 kPa (10 psi) | 39 kPa (6 psi) | 62 kPa (9 psi) |
| Average Range: 47-87 kPa (6.8-12.6 psi) | Replace fuel injector - too much fuel pressure drop | Injector OK | Replace fuel injector - too little fuel pressure drop | Injector OK |
Fuel Injector Balance Test Example (Actual Results May Vary)
The numbers below refer to the step numbers on the diagnostic table.
- 3: The engine coolant temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
- 6: If the pressure drop value for each fuel injector is within 20 kPa (3 psi) of the average pressure drop value, the fuel injectors are flowing properly.
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle | |
| 2 | Did you perform the Fuel Injector Coil Test? | Go to Step 3 | Go to Fuel Injector Coil Test | |
| 3 | IMPORTANT: Do not perform this test if the engine coolant temperature (ECT) is above 94°C (201°F). Observe the ECT parameter with a scan tool.Is the ECT parameter less than the specified value? | 94°C (201°F) | Go to Step 4 | |
| 4 | IMPORTANT: Verify adequate fuel in the fuel tank before proceeding with this diagnostic. Turn OFF the ignition. Install the J 34730-1A Fuel Pressure Gage and the fuel pressure gage fitting. See Special Tools . Refer to Fuel Pressure Gage Installation and Removal . Turn ON the ignition, with the engine OFF. Command the fuel pump relay ON with a scan tool. IMPORTANT: You may need to command the fuel pump relay ON a few times, in order to obtain the highest possible fuel pressure. Do not start the engine. Observe the J 34730-1A with the fuel pump relay commanded ON. See Special Tools . Is the fuel pressure within the specified range? | 384-425 kPa (56-62 psi) | Go to Step 5 | Go to Fuel System Diagnosis |
| 5 | IMPORTANT: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. Monitor the J 34730-1A for 1 minute. See Special Tools .Does the fuel pressure decrease by more than the specified value? | 34 kPa (5 psi) | Go to Fuel System Diagnosis | Go to Step 6 |
| 6 | Connect the J 39021 Fuel Injector Coil/Balancer Tester, the J 39021-210 Injector Selector Switch Box and the J 39021-410 Fuel Injector Harness Adapter to the fuel injector multi-way connector. See Special Tools . Set the amperage supply selector switch on the fuel injector tester to the balance test 0.5-2.5 amp position. Command the fuel pump relay ON and then OFF with a scan tool. Record the fuel pressure indicated by the J 34730-1A after the fuel pressure stabilizes. See Special Tools . This is the first pressure reading. IMPORTANT: Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the fuel injector by depressing the Push to Start test button on the fuel injector tester. Record the fuel pressure indicated by the J 34730-1A . See Special Tools . This is the second fuel pressure reading. Repeat steps 1-6 for each fuel injector. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is more than the average pressure drop or less than the average pressure drop by the specified value? | 20 kPa (3 psi) | Go to Step 7 | Go to Symptoms - Engine Controls |
| 7 | Replace the affected fuel injector. Refer to Fuel Injector Replacement . Did you complete the replacement? | Go to Step 8 | ||
| 8 | Operate the vehicle in order to verify the repair. Does a driveability condition still exist? | Go to Symptoms - Engine Controls | System OK |
| IMPORTANT |
|---|
| Do not perform this test if the engine coolant temperature (ECT) is above 94°C (201°F). |
| IMPORTANT |
|---|
| Verify adequate fuel in the fuel tank before proceeding with this diagnostic. |
| IMPORTANT |
|---|
| You may need to command the fuel pump relay ON a few times, in order to obtain the highest possible fuel pressure. Do not start the engine. |
| IMPORTANT |
|---|
| The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. |
| IMPORTANT |
|---|
| Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. |
Fuel Injector Balance Test with Special Tool
The number below refers to the step number on the diagnostic table.
- 3: The engine coolant temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle | |
| 2 | Did you perform the Fuel Injector Coil Test? | Go to Step 3 | Go to Fuel Injector Coil Test | |
| 3 | IMPORTANT: Do not perform this test if the engine coolant temperature (ECT) is above 94°C (201°F). Observe the ECT parameter with a scan tool.Is the ECT parameter less that the specified value? | 94°C (201°F) | Go to Step 4 | |
| 4 | IMPORTANT: Verify adequate fuel in the fuel tank before proceeding with this diagnostic. Turn OFF the ignition. Turn OFF all the accessories. Install the J 34730-1A Fuel Pressure Gage and the fuel pressure gage fitting. See Special Tools . Refer to Fuel Pressure Gage Installation and Removal . Turn ON the ignition, with the engine OFF. Command the fuel pump ON with a scan tool. IMPORTANT: You may need to command the fuel pump relay ON a few times in order to obtain the highest possible fuel pressure. Do not start the engine. Observe the J 34730-1A , with the fuel pump commanded ON. See Special Tools . Is the fuel pressure within the specified value? | 384-425 kPa (56-62 psi) | Go to Step 5 | Go to Fuel System Diagnosis |
| 5 | IMPORTANT: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. Monitor the J 34730-1A for 1 minute. See Special Tools .Does the fuel pressure decrease by more than the specified value? | 34 kPa (5 psi) | Go to Fuel System Diagnosis | Go to Step 6 |
| 6 | With a scan tool, select the Fuel Injector Balance Test function, within the Special Functions menu. Select a fuel injector to be tested. Press Enter in order to prime the fuel system. Record the fuel pressure indicated by the J 34730-1A after the fuel pressure stabilizes. See Special Tools . This is the 1st pressure reading. IMPORTANT: Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the fuel injector by depressing the Pulse Injector button on the scan tool. This energizes the fuel injector and decreases the fuel pressure. Record the fuel pressure indicated by the J 34730-1A after the fuel injector has stopped pulsing. See Special Tools . This is the 2nd pressure reading. Press Enter again to bring you back to the Select Injector screen. Repeat for each fuel injector. Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by more than the specified value? | 20 kPa (3 psi) | Go to Step 7 | Go to Symptoms - Engine Controls |
| 7 | Replace the affected fuel injector. Refer to Fuel Injector Replacement . Did you complete the replacement? | Go to Step 8 | ||
| 8 | Operate the vehicle in order to verify the repair. Does a driveability condition still exist? | Go to Symptoms - Engine Controls | System OK |
| IMPORTANT |
|---|
| Do not perform this test if the engine coolant temperature (ECT) is above 94°C (201°F). |
| IMPORTANT |
|---|
| Verify adequate fuel in the fuel tank before proceeding with this diagnostic. |
| IMPORTANT |
|---|
| You may need to command the fuel pump relay ON a few times in order to obtain the highest possible fuel pressure. Do not start the engine. |
| IMPORTANT |
|---|
| The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. |
| IMPORTANT |
|---|
| Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. |
Fuel Injector Balance Test with Tech 2
Description
Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start or misfires in one or more cylinders. Water may collect near a single fuel injector at the lowest point in the fuel injection system and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust or deterioration.
Ethanol concentrations of greater than 10 percent can cause driveability conditions and fuel system deterioration. Fuel with more than 10 percent ethanol could result in driveability conditions such as hesitation, lack of power, stalling or no start. Excessive concentrations of ethanol used in vehicles not designed for it may cause fuel system corrosion, deterioration of rubber components and fuel filter restriction.
The manifold absolute pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits
- 5-volt reference circuit
- Low reference circuit
- MAP sensor signal circuit
The control module supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The control module also provides a ground on the low reference circuit. The MAP sensor provides a signal to the control module on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The control module should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The control module should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF or at a wide open throttle (WOT). The MAP sensor is also used in order to determine the barometric pressure (BARO). This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The control module monitors the MAP sensor signal for voltage outside of the normal range.
Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the inspection/maintenance (I/M) emission inspection in order to renew license plates. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that comply with the local area requirements.
The purpose of the Inspection/Maintenance (I/M) complete system set procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics and complete the trips for those particular diagnostics. When all I/M monitored diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform the Inspection/Maintenance (I/M) Complete System Set Procedure if any I/M System Status indicators are set to NO.
The evaporative emission (EVAP) Service Bay Test raises the engine coolant temperature (ECT) threshold so that the temperature sensitive EVAP diagnosis tests can run while in service environments. When the EVAP tests are run the service bay test will indicate a pass or will indicate a specific DTC has failed. The EVAP service bay test can be used to verify an existing condition and verify that the EVAP system is OK after a repair is completed.