G3520B Industrial Engine Caterpillar

Illustration 1	g01087311
Block diagram of the system for the compressor bypass group

The compressor bypass group enables the master Electronic Control Module (ECM) to maintain the desired boost pressure.

Illustration 2	g01087312
Top view Flow of the compressed air/fuel mixture during opening of the compressor bypass group (1) Actuator for the bypass valve (2) Bypass valve

The master ECM monitors the boost pressure sensor. The master ECM uses a map to determine the desired boost pressure for the operating conditions. The master ECM compares the actual boost pressure to the desired boost pressure. The master ECM sends a command signal to actuator (1) in order to modulate the boost pressure. This causes the actuator to move a shaft that is connected to a plate inside bypass valve (2) .

The bypass valve is connected before the throttle. Tubing is connected from the bypass valve to the inlets for the turbocharger compressors. When the bypass valve is opened, the compressed air/fuel mixture is diverted through the tubing away from the throttle. This reduces the boost pressure.

The master ECM is capable of modulating the bypass valve from a fully closed position to a fully opened position.

The compressor bypass group is also operated during engine shutdown. This reduces the opportunity for a turbocharger surge during engine shutdown. Additionally, any air/fuel mixture that may have been trapped in the tubing is purged.

CAN Data Link

The master ECM and the actuator communicate via the CAN data link. The master ECM sends a command signal to the actuator. The actuator sends the following information to the master ECM: actuator position, CCM heartbeat, software version and internal fault diagnosis.

If the master ECM cannot communicate with the actuator, the master ECM activates a 1720-09 diagnostic code and the engine is shut down. A 1720-09 diagnostic code is probably caused by a problem with an electrical connector or a harness. The next likely cause is a problem with the actuator. The least likely cause is a problem with the master ECM.

Terminating resistors must be connected to each end of the CAN data link. The terminating resistors improve the communication between the devices. If there is an intermittent diagnostic code for any of the devices that are connected to the CAN data link, be sure to check the terminating resistor that is inside the terminal box. Also, check the jumper wire that is connected between terminals P and R on the connector for the fuel metering valve. Make repairs, when possible. Replace parts, if necessary.

Identification on the CAN Data Link

When the actuator for the bypass valve is powered up, the actuator looks for a ground on terminal D. If there is a ground on terminal D, the actuator will have a unique identification on the CAN data link.

If there is no ground on terminal D and the actuator is powered up, the actuator for the bypass valve and the throttle actuator will have the same identification. The ECM will not communicate with the actuator for the bypass valve. Instead, the ECM will activate a 1720-09 diagnostic code. The engine will not start.

The electrical connector for the actuator is designed so that the terminals for electrical power are connected before terminal D. For this reason, electrical power must be removed before the connector for the actuator is connected.

Sleep Mode

The actuator for the bypass valve is in sleep mode until terminals P60-C and P60-H are connected. During sleep mode, the actuator consumes less electrical power in order to conserve battery power. The terminals are connected via the contacts of a relay that is inside the terminal box for the master ECM. The relay activates whenever the engine control is not in the OFF mode. If the actuator does not respond, check the circuit for the sleep mode. Make repairs, if necessary.

Illustration 3	g01234821
Schematic for the circuit of the actuator for the compressor bypass

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".

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Illustration 4	g01087098
Terminal box for the master ECM (1) J1/P1 connectors for the master ECM (2) J13/P13 connectors for the termination resistor (3) J5/P5 connectors for the customer's connections (4) J8/P8 connectors for the wiring to the actuator for the bypass valve (5) Relay for the sleep mode (6) J10/P10 connectors for the harness to the optional control panel

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Illustration 5	g01233725
Internal view of the junction box (7) 15 amp fuse for the actuator (8) 6 amp fuse for the keyswitch (9) −Battery connection for the actuator

2. Thoroughly inspect each of the following connectors:
   • J1/P1 connectors

   • J5/P5 connectors

   • J8/P8 connectors

   • J13/P13 connectors

   • Connectors on the actuator for the bypass valve

   1. Check the torque of the allen head screw for the ECM connectors. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the correct torque value.
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   Illustration 6	g01065176
   Harness side of the P1 connector (P1-34) CAN data link − (P1-42) CAN shield (P1-50) CAN data link +

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   Illustration 7	g01087136
   Harness side of the P5 connector (P5-53) CAN data link + (P5-54) CAN data link − (P5-55) CAN shield (P5-63) CAN data link + (P5-64) CAN data link − (P5-65) CAN shield

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   Illustration 8	g01087137
   Harness side of the P8 connector (P8-D) Signal for the sleep mode (P8-F) Signal for the sleep mode (P8-O) CAN data link + (P8-Y) CAN data link − (P8-h) CAN shield (P8-u) Input for the engine control (P8-z) −Battery for the relay

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   Illustration 9	g01087141
   Harness side of the P10 connector (P10-w) Keyswitch (P10-y) Input for the engine control

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   Illustration 10	g01091053
   Harness side of the P60 connector (P60-A) CAN data link − (P60-B) CAN shield (P60-C) Signal for the sleep mode (P60-D) Identification code (P60-H) Signal for the sleep mode (P60-M) CAN data link + (P60-N) −Battery (P60-P) +Battery

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the actuator for the bypass valve.
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   Illustration 11	g01087172
   Actuator for the bypass valve

   3. Check the wiring for corrosion, for abrasion, and for pinch points from the actuator for the bypass valve to the master ECM.

Expected Result:

All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

  Repair: Perform the necessary repairs and/or replace parts, if necessary. Ensure that all of the seals are properly installed. Ensure that the connectors are properly engaged. Verify that the repair has eliminated the original problem.

  STOP

Test Step 2. Check for a Diagnostic Code

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector.

2. Restore the electrical power to the engine. Set the engine control to the STOP mode.

3. Use Cat ET in order to determine if a 1720-09 diagnostic code is active.

Expected Result:

The 1720-09 code is not active.

Results:

• OK - The 1720-09 code is not active. The communication between the master ECM and the actuator for the bypass valve appears to be OK at this time. However, diagnostic codes may be logged.

  Repair: If you are troubleshooting an intermittent problem, refer to Troubleshooting, "Inspecting Electrical Connectors".Terminating resistors must be connected to each end of the CAN data link. The terminating resistors improve the communication between the devices. If there is an intermittent diagnostic code for any of the devices that are connected to the CAN data link, be sure to check the terminating resistor that is inside the terminal box. Also check the jumper wire that is connected between terminals P and R on the connector for the fuel metering valve. Make repairs, when possible. Replace parts, if necessary.

  STOP

• Not OK (Active 1720-09) - The master ECM has detected a problem with the communication between the master ECM and the actuator for the bypass valve. Proceed to Test Step 3.

Test Step 3. Check for Electrical Power at the Actuator

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Illustration 12	g01233628
Locations for the voltage check at the junction box

1. Refer to Illustration 12. Measure the voltage for the actuator at the junction box.

2. Disconnect the electrical connector from the actuator.

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Illustration 13	g01233703
Locations for the voltage check at the harness connector

3. Measure the voltage between terminals N and P at the harness connector.

Expected Result:

The voltage at the harness connector is within two volts of the voltage at the junction box.

Results:

• Yes - The voltage at the harness connector is within two volts of the voltage at the junction box. The actuator is receiving the proper operating voltage. Proceed to Test Step 4.

• No - The voltage at the harness connector is not within two volts of the voltage at the junction box. The actuator is not receiving the proper operating voltage.

  Repair: Determine the cause of the excessive voltage drop. Make the necessary repairs.

  STOP

Test Step 4. Check the CAN Data Link for Continuity between the Actuator for the Bypass Valve and the Master ECM

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Disconnect the P1 connector. Disconnect the connector for the actuator for the bypass valve.

3. Check for continuity between the points that are listed in Table 1. During each measurement, wiggle the harnesses in order to check for an intermittent problem with the harness. Be sure to wiggle the harness near each of the connectors. Be sure to wiggle the harness near the fuel metering valve and the throttle actuator.
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   Table 1

   Points to Check for Continuity
   Connector and Terminal	Harness Connector for the Actuator for the Bypass Valve
   P1-34	Terminal "B" (CAN shield)
   P1-50	Terminal "A" (CAN data link −)
   P1-42	Terminal "M" (CAN data link +)

Expected Result:

The continuity of the circuits between the terminals is good.

Results:

• OK - The continuity of the circuits between the terminals is good. Proceed to Test Step 5.

• Not OK - At least one of the continuity checks indicates an open circuit. There is an open circuit for the CAN data link between the actuator for the bypass valve and the master ECM.

  Repair: The open circuit could be caused by a poor electrical connection in a connector. Alternatively, the open circuit could be caused by one of the following components:

  • The harness inside the terminal box

  • The harness between the terminal box and the throttle actuator

  • The harness between the throttle actuator and the actuator for the bypass valve

  • The fuel metering valve

  • The throttle actuator

  Make repairs, when possible. Replace parts, if necessary.

  STOP

Test Step 5. Check the CAN Data Link for a Short Circuit

1. Disconnect the P2 connector.

2. Use a multimeter to check for continuity between the points that are listed in Table 2. During each measurement, wiggle the harnesses in order to check for an intermittent problem with the harness. Be sure to wiggle the harness near each of the connectors. Be sure to wiggle the harness near the fuel metering valve and the throttle actuator.
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   Table 2

   Points to Check for Continuity
   Connector and Terminal	Connector and Terminal
   P1-34 (CAN data link −)	All of the other terminals on the P1 connector All of the other terminals on the P2 connector Ground strap for the ECM
   P1-50 (CAN data link +)	All of the other terminals on the P1 connector All of the other terminals on the P2 connector Ground strap for the ECM

Expected Result:

All of the measurements indicate an open circuit.

Results:

• OK - All of the measurements indicate an open circuit. The CAN data link does not have a short circuit.

  Repair: Connect the P1 connector and the P2 connector. Connect the connector for the actuator for the bypass valve.

  Proceed to Test Step 6.

• Not OK - At least one of the measurements indicate a short circuit.

  Repair: The short circuit could be caused by a poor electrical connection in a connector. Alternatively, the short circuit could be caused by one of the following components:

  • The harness inside the terminal box

  • The harness between the terminal box and the throttle actuator

  • The harness between the throttle actuator and the actuator for the bypass valve

  • The fuel metering valve

  • The throttle actuator

  Make repairs, when possible. Replace parts, if necessary.

  STOP

Test Step 6. Check for a Diagnostic Code

1. Restore the electrical power to the engine. Set the engine control to the STOP mode.

2. Use Cat ET in order to determine if a 1720-09 diagnostic code is active.

Expected Result:

The 1720-09 code is not active.

Results:

• OK - The 1720-09 code is not active. The problem seems to be resolved. The initial diagnostic code was probably caused by a poor electrical connection.

  Repair: If there is an intermittent problem that is causing the code to be logged, refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The 1720-09 code is active.

  Repair: The active 1720-09 code could be caused by one of the following components:

  • The master ECM

  • The throttle actuator

  • The actuator for the bypass valve

  • The fuel metering valve

  It is unlikely that any of the components that are listed above have failed. Exit this procedure and perform this procedure again. If the 1720-09 code remains active, perform the following procedure:

  1. Temporarily install a new master ECM. Refer to Troubleshooting, "Replacing the ECM". If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Refer to Troubleshooting, "Replacing the ECM". If the problem is not resolved with a new ECM, install the original ECM. Continue with this procedure.

  2. Temporarily install a new throttle actuator. If the new throttle actuator operates correctly, the problem is resolved. If the new throttle actuator does not operate correctly, install the original throttle actuator and continue with this procedure.

  3. Temporarily install a new actuator for the bypass valve. If the new actuator for the bypass valve operates correctly, the problem is resolved. If the new actuator for the bypass valve does not operate correctly, install the original actuator for the bypass valve and continue with this procedure.

  4. Temporarily install a new fuel metering valve. If the new fuel metering valve operates correctly, the problem is resolved. If the new fuel metering valve does not operate correctly, install the original fuel metering valve. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP