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The compression brake uses the engine to provide auxiliary braking for the machine. The compression brake reduces wear of the wheel brake components, brake oil temperature, and the chance for engine overspeed. The compression brake also aids in the controllability of the machine.If the retarder is installed on the engine, the configuration parameter for the engine retarder must be set to "Enabled" for this function to operate. The engine ECM will activate the appropriate compression brake solenoids to meet the requested level of braking."Compression Brake Solenoid Override"The Compression Brake Low/High Override and Compression Brake Med/High Override are diagnostic overrides that are available on Caterpillar Electronic Technician (ET). Use the overrides to help in troubleshooting problems in the circuit for the compression brake. The ECM will only detect shorts in the circuit for the compression brake when the overrides are active. The overrides must be activated and then deactivated before the ECM will detect an open circuit. The ECM will only detect opens in the circuit for the compression brake when the overrides are not active.Note: The engine speed must be zero before the overrides will function.
Illustration 1 g01199118
Location of the compression brake solenoid (typical example)
Illustration 2 g02946837Complete the procedure in the order in which the steps are listed.
Table 2
Troubleshooting Test Steps Values Results
1. Check for Active Diagnostic Codes and/or Logged Diagnostic Codes
A. Connect Cat ET to the service tool connector.
B. Turn the keyswitch to the ON position.
C. Access the diagnostic overrides under the "Diagnostics" menu.
D. Start the "Compression Brake Low/High Override" on Cat ET.
E. Once Cat ET displays the status of the compression brake solenoid, stop the "Compression Brake Low/High Override".
F. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.
G. Start the "Compression Brake Med/High Override" on Cat ET.
H. Once Cat ET displays the status of the compression brake solenoid, stop the "Compression Brake Med/High Override".
I. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.
Diagnostic Trouble Codes
Result: A 2533-5 diagnostic code or a 2535-5 diagnostic code is active now. If both diagnostic codes are active, the problem is most likely in the shared return wire. Inspect the wire and/or connectors for an open circuit.
Proceed to Test Step 2.
Result: A 1072-5 diagnostic code or a 1073-5 diagnostic code is active now. If both diagnostic codes are active, the problem is most likely in the shared return wire. Inspect the wire and/or connectors for an open circuit.
Proceed to Test Step 2.
Result: A 2533-6, diagnostic code or a 2535-6 diagnostic code is active now.
Proceed to Test Step 4.
Result: A 1072-6 diagnostic code or a 1073-6 diagnostic code is active now.
Proceed to Test Step 4.
Table 3
Troubleshooting Test Steps Values Results
2. Create a Short Between the Wires of the Suspect Compression Brake Solenoid at the Valve Cover Connector
To troubleshoot a 2533-5 or 1072-5 diagnostic code, use the "Compression Brake Low/High Override" on Cat ET. To troubleshoot a 2535-5 or 1073-5 diagnostic code, use the "Compression Brake Med/High Override" on Cat ET.
A. Turn the keyswitch to the OFF position.
B. Disconnect the harness at the valve cover connector.
C. Fabricate a jumper wire to create a short between the supply wire for the suspect compression brake solenoid and engine ground.
D. Turn the keyswitch to the ON position.
E. Access the diagnostic overrides under the "Diagnostics" menu.
F. Start the override for the compression brake.
G. Once Cat ET displays the status of the compression brake solenoid, stop the override.
H. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.
I. Turn the keyswitch to the OFF position. Remove the wire short.
A -5 open circuit diagnostic code will be active for the other compression brake solenoid. Ignore the diagnostic codes for the other compression brake solenoid. Ignore any diagnostic codes for the injector solenoids.
Short Circuit Detected
Result: A 2533-6, 1072-6, 1073-6 or a 2535-6 diagnostic code is active now. The harness wiring between the valve cover connector and the ECM is OK.
Proceed to Test Step 3.
Result: A 2533-5, 1072-5, 1073-5 or a 2535-5 diagnostic code is active now. The ECM did not detect the short at the valve cover connector.
Repair: Repair the harness or replace the harness. Verify that the problem is resolved.
Table 4
Troubleshooting Test Steps Values Results
3. Create a Short Circuit at the Compression Brake Solenoid
Two solenoids are activated to create a medium braking action. The open could be in either solenoid or in the harness. To isolate the problem for a medium braking action, run this test step for each of the solenoids. The short must be created separately at each solenoid.
To troubleshoot a 2533-5 or 1072-5 diagnostic code, use the "Compression Brake Low/High Override" on Cat ET. To troubleshoot a 2535-5 or a 1073-5 diagnostic code, use the "Compression Brake Med/High Override" on Cat ET.
A. Turn the keyswitch to the OFF position.
B. Remove the valve cover.
C. Reconnect the valve cover connector.
D. Disconnect the connector on the suspect compression brake solenoid.
E. Inspect the terminals on the connector for the compression brake solenoid for damage.
F. Fabricate a jumper wire to short the two wires for the suspect solenoid on the solenoid connector. Crimp a pin to each end of the jumper wire.
G. Make sure that the solenoid connector securely holds the jumper wire.
Worn terminals and/or damaged terminals on the solenoid connector could cause an intermittent "Open".
H. Turn the keyswitch to the ON position.
I. Access the diagnostic override under the "Diag