G3520B Engines Caterpillar

Compressor Bypass

Usage:

System Operation Description:

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Illustration 1	g00914991
Top view of the engine (1) Inlets for the turbocharger compressors (2) Turbocharger compressor bypass valves (3) Outlet of the aftercooler

Two turbocharger compressor bypass valves (2) are connected between the outlet of the aftercooler (3) and the inlets for the turbocharger compressors (1). Each valve is activated by a solenoid.

When the valves are activated, pressurized air from the aftercooler flows into the intake of the engine. This reduces the boost pressure in the air inlet manifold.

The master ECM activates the solenoids for the valves during these conditions:

Turbocharger surge
Engine shutdown

A rapid reduction in the generator's power output can cause the engine's speed to rapidly increase. The increased engine speed causes the turbochargers to produce boost pressures that are greater than the requirement for engine operation.

The generator's switchgear contains a generator output power sensor. This sensor produces a low voltage signal that indicates the amount of power that is being produced by the generator. The sensor's signal is sent to the master ECM. The master ECM continuously monitors the signal from the sensor. The master ECM responds to a rapid drop in the signal from the sensor by activating the solenoids. The solenoids open the valves.

The valves allow the compressed air/fuel mixture in the aftercooler to flow into the intake of the compressor. This reduces the pressure that is created by the compressor.

Engine shutdown occurs when the output for the fuel control relay is OFF and the engine RPM is above 100. The master ECM activates the output for the solenoids until the engine RPM drops to zero. This scavenges any unburned gases in the components of the system during engine shutdown.

A "Turbocharger Compressor Bypass Valve Solenoid" diagnostic code is probably caused by a problem with an electrical connector or a harness. The next likely cause is a problem with a solenoid. The least likely cause is a problem with the master ECM.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.

This procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the logged codes after the problem is resolved.

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Illustration 2	g00993419
Schematic of the circuit for the solenoids

Test Step 1. Inspect the Electrical Connectors and Wiring

Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

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

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Illustration 3	g00995487
(1) Ground strap (2) J2/P2 connectors for the master ECM (3) J1/P1 connectors for the master ECM (4) J10/P10 connector for the harness from the solenoids (5) 16 amp circuit breaker

Thoroughly inspect the following connectors:
- Master ECM J1/P1 and J2/P2 connectors
- J10/P10 connectors on the terminal box
1. Check the torque of the Allen head screw for the ECM connectors. The proper torque is 6 ± 1 N·m (55 ± 9 lb in).
1. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the solenoids.
1. Thoroughly inspect connectors (7) for solenoids (6). Verify that connectors (7) do not have moisture or contamination. Check the harness and wiring for abrasion and for pinch points from each solenoid to the master ECM.

Expected Result:

The connectors and terminals are connected properly. The connectors are free of moisture and of corrosion. 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.
STOP

Test Step 2. Check the Low Side Wire for a Short to the +Battery

Disconnect the connectors for both of the solenoids.

Disconnect the P1 and P2 connectors.

Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

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Illustration 7	g00906771
(1) Ground strap (P2-7) Low side wire for the solenoids

Measure the voltage between terminal P2-7 and ground strap (1) for the ECM.

Expected Result:

The voltage is approximately zero volts.

Results:

OK - The voltage at terminal P2-7 is approximately zero volts. The low side wire does not have a short circuit to the +battery side. Proceed to Test Step 3.
Not OK - The voltage at terminal P2-7 is approximately equal to the +battery voltage. The low side wire has a short circuit to the +battery side. The short circuit could be inside the terminal box or in the engine harness.
Repair: Repair the connector and/or the harness, when possible. Replace the harness, if necessary.
STOP

Test Step 3. Check the Low Side Wire for a Short to Ground

Switch the 16 amp circuit breaker OFF. Set the engine control to the OFF/RESET mode.

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Illustration 8	g00907693
Harness connectors and jumper wire (1) Jumper wire (P2-7) Low side wire for the solenoids (P1-70) Switched +battery

Install a jumper wire between terminals P2-7 and P1-70.

Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

Expected Result:

The 16 amp circuit breaker does not trip.

Results:

OK - When the low side wire is connected to the +battery side, the 16 amp circuit breaker does not trip. The low side wire does not have a short to ground. Proceed to Test Step 4.
Not OK - When the low side wire is connected to the +battery side, the 16 amp circuit breaker trips. The low side wire has a short to ground. The short could be inside the terminal box or in the engine harness.
Repair: Repair the connector and/or the harness, when possible. Replace the harness, if necessary.
STOP

Test Step 4. Check the Low Side Wire for an Open Circuit

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Illustration 9	g00907784
Side view of a turbocharger compressor bypass valve (1) Terminal B (2) Harness connector

At the harness connector for the solenoid on the left side of the engine, measure the voltage between terminal B and the engine block. Record the measurement.

At the harness connector for the solenoid on the right side of the engine, measure the voltage between terminal B and the engine block. Record the measurement.

Expected Result:

Both of the voltage measurements are approximately equal to the +battery voltage.

Results:

OK - Both of the voltage measurements are approximately equal to the +battery voltage. The low side wire does not have an open circuit. Proceed to Test Step 5.
Not OK - At least one of the voltage measurements is not approximately equal to the +battery voltage. The low side wire has an open circuit. The open circuit could be inside the terminal box or in the engine harness.
Repair: Repair the connector and/or the harness, when possible. Replace the harness, if necessary.
STOP

Test Step 5. Check the High Side Wire for a Short to the +Battery

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Illustration 10	g00910721
(1) Ground strap (P2-6) High side wire for the solenoids

Measure the voltage between terminal P2-6 and ground strap (1) for the ECM.

Expected Result:

The voltage measurement is approximately zero volts.

Results:

OK - The voltage measurement at terminal P2-6 is approximately zero volts. The high side wire does not have a short circuit to the +battery side. Proceed to Test Step 6.
Not OK - The voltage measurement at terminal P2-6 is approximately equal to the +battery voltage. The high side wire has a short circuit to the +battery side. The short circuit could be inside the terminal box or in the engine harness.
Repair: Repair the connector and/or the harness, when possible. Replace the harness, if necessary.
STOP

Test Step 6. Check the High Side Wire for a Short to Ground

Switch the 16 amp circuit breaker OFF. Set the engine control to the OFF/RESET mode.

Remove the end of the jumper wire from terminal P2-7.

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Illustration 11	g00907741
Harness connectors and jumper wire (1) Jumper wire (P2-6) High side wire for the solenoids (P1-70) Switched +battery

Install the end of jumper wire (1) into terminal P2-6. The jumper wire should be connected between terminals P2-6 and P1-70.

Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

Expected Result:

The 16 amp circuit breaker does not trip.

Results:

OK - When the high side wire is connected to the +battery side, the 16 amp circuit breaker does not trip. The high side wire does not have a short to ground. Proceed to Test Step 7.
Not OK - When the high side wire is connected to the +battery side, the 16 amp circuit breaker trips. The high side wire has a short to ground. The short circuit could be inside the terminal box or in the engine harness.
Repair: Repair the connector and/or the harness, when possible. Replace the harness, if necessary.
STOP

Test Step 7. Check the High Side Wire for an Open Circuit

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Illustration 12	g00907732
Side view of a turbocharger compressor bypass valve (1) Harness connector (2) Terminal A

At the harness connector for the solenoid on the left side of the engine, measure the voltage between terminal A (2) and the engine block. Record the measurement.

At the harness connector for the solenoid on the right side of the engine, measure the voltage between terminal A and the engine block. Record the measurement.

Expected Result:

Both of the voltage measurements are approximately equal to the +battery voltage.

Results:

OK - Both of the voltage measurements are approximately equal to the +battery voltage. The high side wire does not have an open circuit. Proceed to Test Step 8.
Not OK - At least one of the voltage measurements is not approximately equal to the +battery voltage. The high side wire has an open circuit.
Repair: Repair the connector and/or the harness, when possible. Replace the harness, if necessary.
STOP

Test Step 8. Check the Solenoid on the Left Side of the Engine for a Short Circuit

Connect the connector for the solenoid on the left side of the engine. Listen for an audible click from the solenoid as the connector is connected.
If the ambient noise is too loud, touch the solenoid when the connector is connected in order to feel the vibration. The solenoid will vibrate when the connector is connected.

Expected Result:

The solenoid does not energize.

Results:

OK - When the solenoid on the left side of the engine is connected, the solenoid does not energize. The solenoid does not have an internal short circuit.
Repair: Disconnect the harness connector for the solenoid on the left side of the engine.
Proceed to Test Step 9.
Not OK - When the solenoid on the left side of the engine is connected, the solenoid energizes. The solenoid has an internal short circuit.
Repair: Replace the turbocharger compressor bypass valve on the left side of the engine.
STOP

Test Step 9. Check the Solenoid on the Right Side of the Engine for a Short Circuit

Connect the harness connector for the solenoid on the right side of the engine. Listen for an audible click from the solenoid as the connector is connected.
If the ambient noise is too loud, touch the solenoid when the connector is connected in order to feel the vibration. The solenoid will vibrate when the connector is connected.

Expected Result:

The solenoid does not energize.

Results:

OK - When the solenoid on the right side of the engine is connected, the solenoid does not energize. The solenoid does not have an internal short circuit.
Repair: Disconnect the harness connector for the solenoid on the right side of the engine.
Proceed to Test Step 10.
Not OK - When the solenoid on the right side of the engine is connected, the solenoid energizes. The solenoid has an internal short circuit.
Repair: Replace the turbocharger compressor bypass valve on the right side of the engine.
STOP

Test Step 10. Check the Solenoid on the Left Side of the Engine for an Open Circuit

Switch the 16 amp circuit breaker OFF. Set the engine control to the OFF/RESET mode.

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Illustration 13	g00907751
Harness connectors and jumper wires (1) Jumper wire (P2-7) Low side wire for the solenoids (P1-65) -Battery

Install a jumper wire between terminals P2-7 and P1-65. Two jumper wires should be installed between the connectors.

Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

Connect the connector for the solenoid on the left side of the engine. Listen for an audible click from the solenoid as the connector is connected.
If the ambient noise is too loud, touch the solenoid when the solenoid is connected in order to feel the vibration. The solenoid will vibrate when the connector is connected.

Expected Result:

The solenoid is energized when the solenoid's connector is connected.

Results:

OK - When the connector for the solenoid on the left side of the engine is connected, the solenoid is energized. The solenoid does not have an open circuit. Proceed to Test Step 11.
Not OK - When the connector for the solenoid on the left side of the engine is connected, the solenoid is not energized. The solenoid has an open circuit.
Repair: Replace the turbocharger compressor bypass valve on the left side of the engine.
STOP

Test Step 11. Check the Solenoid on the Right Side of the Engine for an Open Circuit

Connect the connector for the solenoid on the right side of the engine. Listen for an audible click from the solenoid as the connector is connected.
If the ambient noise is too loud, touch the solenoid when the solenoid is connected in order to feel the vibration. The solenoid will vibrate when the connector is connected.

Expected Result:

The solenoid is energized when the solenoid's connector is connected.

Results:

OK - When the connector for the solenoid on the right side of the engine is connected, the solenoid is energized. The solenoid does not have an open circuit.
Repair: Perform the following procedure:
1. Switch the 16 amp circuit breaker OFF. Set the engine control to the OFF/RESET mode.
1. Remove the two jumper wires from the P1 and P2 connectors.
1. Reconnect the J1/P1 connectors and the J2/P2 connectors.
Proceed to Test Step 12.
Not OK - When the connector for the solenoid on the right side of the engine is connected, the solenoid is not energized. The solenoid has an open circuit.
Repair: Replace the turbocharger compressor bypass valve on the right side of the engine.
STOP

Test Step 12. Check for Diagnostic Codes

Start the engine and run the engine to high idle.

Set the engine control to the STOP mode.

Expected Result:

Neither of the following diagnostic codes are activated:

1720-05 Turbo Compressor Bypass Valve Solenoid open
1720-06 Turbo Compressor Bypass Valve Solenoid shrt to gnd

Results:

OK - When the engine was shut down, no diagnostic codes were activated for the solenoids. The problem appears to be resolved. The problem may have been caused by a poor electrical connection.STOP
Not OK - When the engine was shut down, a diagnostic code was activated for the solenoids. The master ECM may have a problem.
Repair: It is unlikely that the master ECM has failed. Perform this entire procedure again. If the problem is not resolved, 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".
STOP