3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Use this procedure if any of the following diagnostic codes are present:

• 1-11 Cylinder 1 Fault (72)

• 2-11 Cylinder 2 Fault (72)

• 3-11 Cylinder 3 Fault (73)

• 4-11 Cylinder 4 Fault (73)

• 5-11 Cylinder 5 Fault (74)

• 6-11 Cylinder 6 Fault (74)

Also use this procedure if you have been referred to this test from Troubleshooting, "Engine Misfires, Runs Rough or Is Unstable " or Troubleshooting, "Low Power/Poor or No Response to Throttle".

Perform this procedure under conditions that are identical to the conditions that exist when the problem occurs. Typically, problems with the injector solenoid occur when the engine is warmed up and/or when the engine is under vibration (heavy loads).

The following background information is related to this procedure:

The engines use Hydraulic Electronic Unit Injectors that are hydraulically actuated and electronically energized. The solenoid is mounted on top of the fuel injector body.

The injectors can be individually cut out to aid in troubleshooting misfire problems. Use the Cylinder Cutout Test to disable individual injectors.

The injector solenoids can also be actuated without running the engine in order to check the operation of the solenoids. Use the Injector Solenoid Test to perform this function.

Note: The Injector Solenoid Test will not help find leaks in the high pressure oil system.

Illustration 1	g00723522

Illustration 2	g00782844
Circuit schematic for the injectors

Test Step 1. Inspect Electrical Connectors and Wiring.

Illustration 3	g00723444
Pin locations for ECM

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key is not turned OFF.

2. Thoroughly inspect the ECM engine harness connector J2/P2 and the solenoid connector for the injector J300/P300. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the solenoid connector for the injector J300/P300 that are associated with injector solenoids.

   Refer to Illustration 3.

4. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

5. Check the solenoid connector for the injector J300/P300 in order to ensure the proper mating of the connector.

6. Check the harness and wiring for abrasion and pinch points from the injectors to the ECM.

Expected Result:

All connectors, pins and sockets should be completely coupled and/or inserted and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - Proceed to Test Step 2.

• Not OK -

  Repair: Perform the following repair:Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Use ET to Check for Logged Diagnostic Codes.

1. Connect ET to the cab data link connector.

2. Turn the ignition key switch to the ON position.

3. Monitor the "Logged Diagnostic Code" screen of ET.

Expected Result:

One or more of the listed codes have been logged:

• 1-11 Cylinder 1 Fault (72)

• 2-11 Cylinder 2 Fault (72)

• 3-11 Cylinder 3 Fault (73)

• 4-11 Cylinder 4 Fault (73)

• 5-11 Cylinder 5 Fault (74)

• 6-11 Cylinder 6 Fault (74)

Results:

• Yes - Proceed to Test Step 4.

• No - Proceed to Test Step 3.

Test Step 3. Check the Variation of the Injectors From Cylinder to Cylinder.

1. Connect ET to the cab data link connector.

2. When possible, put the truck on a dynamometer.

3. Start the engine.

4. Allow the engine to warm up to normal operating temperature 77 °C (171 °F).

5. After the engine is warmed to operating temperature, access the "Cylinder Cutout Test" by accessing the following display screens in order:
   • "Diagnostics"

   • "Diagnostic Tests"

   • "Cylinder Cutout Test"

6. Enable the cooling fan, if the fan is not controlled by the ECM. If the ECM controls the cooling fan, the cooling fan will start automatically when the test begins.

7. Shut off all parasitic loads such as the air conditioning and the air compressors which could affect the results of the test.

8. Cut out each cylinder and watch the "Fuel Position" of all of the other cylinders.

9. Verify that cutting out a specific cylinder causes only a slight change to the Fuel Position of the other cylinders in comparison to the change to the Fuel Position that occurs when other cylinders are cut out. If a cylinder is cut out and only a slight change occurs to the Fuel Position of the other cylinders, a mechanical problem with the injector or a mechanical problem with the cylinder may exist.

10. After the test is finished, use ET to check for active diagnostic codes or for logged diagnostic codes that are new.

Expected Result:

An active diagnostic code for a cylinder fault results from running the Cylinder Cutout Test.

Results:

• Yes - Proceed to Test Step 4.

• No - Perform the following repair:

  Repair: If a cylinder is cut out and only a slight change occurs to the Fuel Position of the other cylinders, a mechanical problem with the injector or a mechanical problem with the cylinder may exist. If the engine is misfiring or if the engine has low power, refer to Troubleshooting, "Engine Misfires, Runs Rough or Is Unstable" and Troubleshooting, "Low Power/Poor or No Response to Throttle".

  If a diagnostic code for a cylinder fault results from running the Cylinder Cutout test, proceed to Test Step 4.

Test Step 4. Use the Injector Solenoid Test to Test the Injector Solenoids.

1. Start the engine.

2. Allow the engine to warm up to 77 °C (171 °F) which is the normal operating temperature.

3. Turn the ignition key switch to the OFF position.

4. Connect ET at the cab data link connector.

5. Turn the ignition key switch to the ON position.

6. After the engine is warmed to operating temperature, access the "Injector Solenoid Test" by accessing the following display screens in order:
   • "Diagnostics"

   • "Diagnostic Tests"

   • "Injector Solenoid Test"

7. Activate the test.

   Note: Do not confuse the Injector Solenoid Test with the Cylinder Cutout Test. The Cylinder Cutout Test is used to shut off fuel to a specific cylinder while the engine is running. The Injector Solenoid Test is used in order to actuate the injector solenoids. This allows the click of the injector solenoids to be heard when the engine is not running in order to determine that the circuit is functioning properly.

8. As each solenoid is energized by the ECM an audible click can be heard at the valve cover. A black square will appear over the cylinder number when the cylinder is being fired.

9. Perform the Injector Solenoid Test at least two times.

Expected Result:

All cylinders indicate "OK".

Results:

• Yes - There is not an electronic problem with the injectors at this time.STOP

• No - ET displays "SHORT" for any cylinder. Proceed to Test Step 5.

• No - ET displays "OPEN" for any cylinder. Proceed to Test Step 6.

Test Step 5. Check the Injector Harness from P2 to J300 for Short Circuits.

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key switch is not turned off.

2. Disconnect the 12-pin connector (J300/P300). Check for evidence of moisture entry. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Turn the ignition key switch to the ON position.

4. Access the "Injector Solenoid Test" on ET and begin the test.

Expected Result:

The status of the circuit for the suspect injector displays "SHORT" before J300/P300 is disconnected. The status of the circuit for the suspect injector changes to "OPEN" after J300/P300 is disconnected.

Results:

• Yes - Reconnect J300/P300. Proceed to Test Step 7.

• No - Proceed to Test Step 8.

Test Step 6. Check the Injector Harness from P2 to J300 for an Open Circuit.

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key switch is not turned off.

2. Disconnect the 12-pin connector (J300/P300).

3. Insert one end of a jumper wire into the socket of the suspect injector. Insert the other end of the jumper wire into the socket of the injector common line for the connector (J300/P300).

4. Turn the ignition key switch to the ON position.

5. Access the "Injector Solenoid Test" on ET and begin the test.

Expected Result:

The status of the circuit for the suspect injector displays "OPEN" before J300/P300 is disconnected. The status of the circuit for the suspect injector changes to "SHORT" after J300/P300 is disconnected.

Results:

• Yes - Proceed to Test Step 9.

• No - Proceed to Test Step 10.

Test Step 7. Check the Injector Harness for a Short Circuit Between Connector P300 and the Injector.

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key is not turned OFF.

2. Remove the valve cover.

3. Disconnect the harness from the problem injector at the connector that is attached to the injector solenoid. For example, if the number one injector is the suspect injector, disconnect P301 from J301.

4. Turn the ignition key switch to the ON position.

5. Access the "Injector Solenoid Test" on ET and perform the test three times.

   Note: Ensure that the seal is installed in the harness connector before connecting the harness to the connector. If the seal is missing, use a replacement seal. Ensure that the seal is not stuck in the injector connector.

Expected Result:

The status for the injector that is disconnected changes to "OPEN" when the harness is disconnected.

Results:

• Yes - Perform the following repair:

  Repair: Temporarily connect a new injector to the harness. Run the "Injector Solenoid Test". If all cylinders indicate "OK", turn the keyswitch to OFF and reconnect the old injector. If the original injector again reads "OPEN", replace the injector. Restore the wiring to the proper injectors. Use the "Injector Solenoid Test" to verify that the repair eliminates the problem.Do not install the valve cover until the problem is resolved. Clear all diagnostic codes.

  STOP

• No - Perform the following repair:

  Repair: There is a short in the wiring harness. Replace the wiring harness between the 12-pin connector (P300) and the injector.Verify that the repair eliminates the problem.

  STOP

Test Step 8. Use the "Injector Solenoid Test" to Check for Short Circuits in the ECM and in the Harness.

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key is not turned OFF.

2. Disconnect ECM engine harness connector "J2/P2" from the ECM and check for evidence of moisture entry. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Turn the ignition key switch to the ON position.

4. Access the "Injector Solenoid Test" on ET and begin the test.

   Note: When ECM Connector J2/P2 is disconnected, all of the open circuit diagnostic codes for the sensors and the open circuit diagnostic code for the Air Inlet Heater will be active. This is normal. Clear all diagnostic codes after completing this test step.

Expected Result:

All cylinders indicate "OPEN" when the engine harness connector P2 is disconnected from the ECM.

Results:

• Yes - Repair the harness between the ECM Connector P2 and the 12-pin connector (J300). If the harness cannot be repaired, replace the harness.STOP

• No - Temporarily connect a test ECM. Repeat this test step. If the problem is resolved with the test ECM, install the old ECM in order to verify that the problem returns. If the test ECM works and the old ECM does not work, replace the ECM.STOP

Test Step 9. Check the Injector Harness for an Open Circuit Between Connector P300 and the Injector.

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key is not turned OFF.

2. Remove the valve cover.

3. Disconnect the harness from the problem injector at the connector that is attached to the injector solenoid. For example, if the number one injector is the suspect injector, disconnect P301 from J301.

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Illustration 4	g00723455
Connector for injector solenoids

4. Insert a jumper wire across the terminals of the harness connector that was removed from the injector. For example, if the number one injector is the suspect injector, place the jumper wire across the terminals of "P301".

5. Turn the ignition key switch to the ON position.

6. Access the "Injector Solenoid Test" on ET and monitor the cylinder.

Expected Result:

The status of the injector with the short in place indicates an "OPEN".

Results:

• Yes - There is an open circuit in the harness. Repair the harness between the 12-pin connector (J300) and the injector. Replace the harness if the harness cannot be repaired. Verify that the repair eliminates the problem.STOP

• No -

  Repair: Temporarily connect a new injector to the harness. Run the "Injector Solenoid Test". If all cylinders indicate "OK", turn the keyswitch to OFF and reconnect the old injector. If the original injector again reads "OPEN", replace the injector. Restore the wiring to the proper injectors. Use the "Injector Solenoid Test" to verify that the repair eliminates the problem.Do not install the valve cover until the problem is resolved. Clear all diagnostic codes.

  STOP

Test Step 10. Use the "Injector Solenoid Test" to Check for Open Circuits in the ECM and in the Harness.

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Electrical shock hazard. The electronic unit injector system uses 90-120 volts.

1. Turn the ignition key switch to the OFF position. A strong electrical shock hazard is present if the ignition key is not turned OFF.

2. Disconnect ECM engine harness connector "J2/P2" from the ECM and check for evidence of moisture entry. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Connect a 70-Terminal breakout T into the ECM. Do not connect the engine harness connector P2 into the breakout T.

4. Use a jumper wire to short between the socket of the suspect injector and the common socket of the suspect injector.

5. Turn the ignition key switch to the ON position.

6. Access the "Injector Solenoid Test" on ET and begin the test.

   Note: When ECM connector J2/P2 is disconnected, all of the open circuit diagnostic codes for the sensors and the open circuit diagnostic code for the air inlet heater will be active. All of the injectors that are not jumpered will indicate an OPEN circuit during the "Injector Solenoid Test". This is normal. Clear all diagnostic codes after completing this test step.

Expected Result:

ET displays "SHORT" for the cylinder with the jumper wire.

Results:

• Yes - Repair the harness between the 12-pin connector (J300) and the ECM connector P2. Replace the harness if the harness cannot be repaired.STOP

• No - Temporarily connect a test ECM. Repeat this test step. If the problem is resolved with the test ECM, install the old ECM in order to verify that the problem returns. If the test ECM works and the old ECM does not work, replace the ECM.STOP