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3456 Engine, 836G Landfill Compactor, 834G Wheel Dozer and 988G Wheel Loader Caterpillar


Compression Brake Solenoid Circuit - Test

Usage:

988G 2TW
System Operation Description:

The compression brake uses the engine in order to provide auxiliary braking. The compression brake reduces engine overspeed, brake oil temperature, and the wear of brake components.

The compression brake has two modes of operation, manual mode and automatic mode. The compression brake is in manual mode when the compression brake switch is in the ON position. While the compression brake is in manual mode the compression brake solenoids will activate when the engine speed goes above 1300 rpm. The compression brake solenoids will remain active in manual mode until the engine speed falls below 950 rpm.

The compression brake is in auto mode when the compression brake switch is in the OFF position. While the compression brake is in auto mode the compression brake solenoids will activate when the engine speed is above 2275 rpm. The compression brake solenoids will remain active in auto mode until the engine speed falls below 2275 rpm. The auto mode is intended to prevent engine overspeed.

Note: The compression brake will be disabled if the engine is running in cold mode. The throttle lock will be disabled when the engine compression brake is activated.

Show/hide table
Illustration 1g00735884
Schematic

Test Step 1. Check for Connector Damage

  1. Turn the keyswitch to the OFF/RESET position.

  2. Check ECM connectors J1/P1 and J2/P2, injector connector J91/P91, and the associated wiring for the following problems: damage, corrosion, abrasion and incorrect attachment. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

Expected Result:

The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

  • OK - Proceed to Test Step 2.

  • Not OK -

    Repair: Repair the circuit.

    Verify that the repair eliminates the problem.

    STOP

Test Step 2. Check for Active/Logged Diagnostic Codes on ET

  1. Connect ET to the service tool connector.

  2. Turn the keyswitch to the ON position.

  3. Observe any diagnostic codes on ET.

  4. Turn the keyswitch to the OFF/RESET position.

Expected Result:

The following diagnostic codes should not be active or logged:

  • 791-05 Jake Brake Low/High Solenoid open circuit

  • 791-06 Jake Brake Low/High Solenoid short to ground

  • 792-05 Jake Brake Medium/High Solenoid open circuit

  • 792-06 Jake Brake Medium/High Solenoid short to ground

Results:

  • OK - None of the above diagnostic codes are present. Proceed to Test Step 8.

  • Not OK - One or more of the above diagnostic codes are present. Proceed to Test Step 3.

Test Step 3. Test the Compression Brake Solenoids by using ET

  1. Connect ET to the service tool connector.

  2. Turn the keyswitch to the ON position.

  3. Run the "Retarder Solenoid Override Test". Listen for the compression brake solenoids to click as the solenoids are activated by ET.

  4. Turn the keyswitch to the OFF/RESET position.

Expected Result:

Each of the compression brake solenoids should click as the solenoid is activated by ET.

Results:

  • OK - The solenoids are operating normally.

    Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

    STOP

  • Not OK - Proceed to Test Step 4.

Test Step 4. Test the Engine Harness with ET

  1. Connect ET to the service tool connector.

  2. Disconnect the connector J91/P91 at the valve cover.

  3. Turn the keyswitch to the ON position.

  4. Install a circuit test light between P91:7 (Compression Brake Solenoid Return) and P91:9 (Compression Brake Solenoid Low/High).

  5. Run the "Retarder Solenoid Override Test" and observe the circuit test light.

  6. Move one of the leads on the circuit test light from P91:9 (Compression Brake Solenoid Low/High) to P91:11 (Compression Brake Solenoid Medium/High). Leave the other lead connected to P91:7 (Compression Brake Solenoid Return).

  7. Run the "Retarder Solenoid Override Test" and observe the circuit test light.

  8. Turn the keyswitch to the OFF/RESET position.

  9. Remove the circuit test light and reconnect the connector J91/P91 at the valve cover.

    Note: Additional diagnostic codes will be generated because the connector J91/P91 was disconnected at the valve cover and the "Retarder Solenoid Override Test" was run. Clear the additional diagnostic codes upon completing this test.

Expected Result:

The circuit test light should turn on when the test is active. The circuit test light should otherwise remain off.

Results:

  • OK - The engine harness is operating normally.

    Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

    Proceed to Test Step 6.

  • Not OK - Proceed to Test Step 5.

Test Step 5. Check the ECM

  1. Connect ET to the service tool connector.

  2. Turn the keyswitch to the OFF position.

  3. Connect a 7X-1715 Adapter Cable (40 Pin Breakout) to the ECM connector J2/P2.

  4. Turn the keyswitch to the ON position.

  5. Install a circuit test light between P2:7 (Compression Brake Solenoid Return) and P2:19 (Compression Brake Solenoid Low/High) at the breakout.

  6. Run the "Retarder Solenoid Override Test" and observe the circuit test light.

  7. Move one of the leads on the circuit test light from P2:19 (Compression Brake Solenoid Low/High) to P2:13 (Compression Brake Solenoid Medium/High) on the breakout. Leave the other lead connected to P2:7 (Compression Brake Solenoid Return).

  8. Run the "Retarder Solenoid Override Test" and observe the circuit test light.

  9. Turn the keyswitch to the OFF/RESET position.

  10. Remove the circuit test light and the breakout, and reconnect the ECM connector J2/P2.

    Note: Additional diagnostic codes will be generated because the ECM engine harness connector J2/P2 was disconnected and the "Retarder Solenoid Override Test" was run. Clear the additional diagnostic codes upon completing this test.

Expected Result:

The circuit test light should turn on when the test is active. The circuit test light should otherwise remain off.

Results:

  • OK - The circuit test light turns on during the test, and the ECM is working properly.

    Repair: There is an open or a short between the ECM and the connector P91. Repair the circuit.

    Verify that the repair eliminates the problem.

    STOP

  • Not OK - Correct inputs appear at the ECM connector P2 but the ECM is not reading the inputs properly.

    Repair: Verify your results. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.

    STOP

Test Step 6. Check for Damage to the Wiring Harness that is Under the Valve Cover

  1. Check the harness connector J91, the solenoid connectors, and the associated wiring that is under the valve cover for the following problems: damage, corrosion, abrasion and incorrect attachment. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

Expected Result:

The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

  • OK - Proceed to Test Step 7.

  • Not OK -

    Repair: Repair the circuit.

    Verify that the repair eliminates the problem.

    STOP

Test Step 7. Test the Wiring Harness that is Under the Valve Cover by using ET

  1. Connect ET to the service tool connector.

  2. Disconnect the wiring harness from all of the compression brake solenoids that do not respond during the "Retarder Solenoid Overide Test".

  3. Turn the keyswitch to the ON position.

  4. On the wiring harness, install a circuit test light between one pair of terminals that was disconnected from the solenoid. Only one pair of terminals should be tested at a time.

    Note: Take proper steps in order to prevent any of the terminals from shorting to the engine while the following test is performed.

  5. Run the "Retarder Solenoid Override Test" and observe the circuit test light.

  6. Repeat the above steps for all other pairs of terminals that have been disconnected from the solenoid.

  7. Turn the keyswitch to the OFF/RESET position.

  8. Remove the circuit test light and reconnect the compression brake solenoid connectors.

    Note: Additional diagnostic codes will be generated because all the compression brake solenoid connectors were not connected and the "Retarder Solenoid Override Test" was run. Clear the additional diagnostic codes upon completing this test.

Expected Result:

The circuit test light should turn on when the test is active. The circuit test light should otherwise remain off.

Results:

  • OK - The wiring harness that is under the valve cover is operating normally.

    Repair: Replace all of the compression brake solenoids that do not respond during the "Retarder Solenoid Overide Test".

    Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

    STOP

  • Not OK - The wiring harness that is under the valve cover is not working properly.

    Repair: Repair the wiring harness that is under the valve cover.

    Verify that the repair eliminates the problem.

    STOP

Test Step 8. Check the Switch Status on ET

  1. Connect ET to the service tool connector.

  2. Turn the keyswitch to the ON position.

  3. Operate the compression brake switch.

  4. Observe the status for "Retarder Switch" on ET.

  5. Turn the keyswitch to the OFF/RESET position.

Expected Result:

The status of the switch should read "Manual" with the switch in the ON position. The status should read "Auto" with the switch in the OFF position.

Results:

  • OK - The switch is operating normally.

    Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

    STOP

  • Not OK - Proceed to Test Step 9.

Test Step 9. Short the Switch Inputs at the Switch

Record the switch wiring before removing the wires.

  1. Connect ET to the service tool connector.

  2. Disconnect all the wires from the compression brake switch.

  3. Use a suitable piece of wire to short C998-BR(Brown) and N943-BR(Brown) together.

  4. Turn the keyswitch to the ON position.

  5. Observe the status for "Engine Retarder" on ET.

  6. Remove the wire short between C998-BR(Brown) and N943-BR(Brown).

  7. Observe the status for "Engine Retarder" on ET.

  8. Turn the keyswitch to the OFF/RESET position.

Expected Result:

The status of the switch should read "Manual" when C998-BR(Brown) and N943-BR(Brown) are shorted together. Otherwise, the status should read "Auto".

Results:

  • OK - The problem is not with the harness and/or the ECM.

    Repair: Temporarily connect a new switch. Verify that the new switch solves the problem before you permanently install the new switch.

    STOP

  • Not OK - There is a problem in the harness and/or the ECM. Proceed to Test Step 10.

Test Step 10. Short the Switch Inputs at the ECM

Show/hide table
Illustration 2g00747691
ECM Connector P1 (wire insertion side)

  1. Connect ET to the service tool connector.

  2. Turn the keyswitch to the OFF position.

  3. Turn the compression brake switch to the OFF position.

  4. Connect a 7X-1715 Adapter Cable (40 Pin Breakout) to the ECM connector J1/P1.

  5. Use a suitable piece of wire to short P1:23 (Compression Brake Manual Switch) and P1:29 (Digital Return) at the breakout.

  6. Turn the keyswitch to the ON position.

  7. Observe the status for "Retarder Switch" on ET.

  8. Remove the wire short from the breakout.

  9. Observe the status for "Retarder Switch" on ET.

  10. Turn the keyswitch to the OFF/RESET position.

  11. Remove the breakout and reconnect the ECM connector J1/P1.

Expected Result:

The status for "Retarder Switch" should read "Manual" when there is a short between P1:23 (Compression Brake Manual Switch) and P1:29 (Digital Return). Otherwise, the status should read "Auto".

Results:

  • OK - The ECM is working properly.

    Repair: The wiring harness is not working properly. Repair the wiring harness.

    Verify that the repair eliminates the problem.

    STOP

  • Not OK - Correct switch inputs appear at the ECM connector P1 but the ECM is not reading the inputs properly.

    Repair: Verify your results. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.

    STOP

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