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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 engine is equipped with engine compression brakes, the "Engine Retarder Enable Command" parameter must be set to "Enabled" in order for this function to operate.The auto mode is selected when the engine retarder switch is in the released position. In auto mode, the retarder will be activated only when the engine speed is above 2100 rpm. The retarder will remain on until the engine speed falls below 1750 rpm.The manual mode is selected when the engine retarder switch is actuated continuously by the operator. In the manual mode, the engine retarder will be activated only when the engine speed is above 1500 rpm. The retarder will remain on until the engine speed falls below 1400 rpm, or the engine retarder switch is released.When the compression brake is activated, the engines Electronic Control Module (ECM) disengages the throttle lock, the fuel injection, and the ether control.While compression brake operation is directly controlled by the engine ECM, the transmission ECM provides an interlock control for protection of the transmission and of the drive train. This interlock control ensures that the operating conditions for the engine, the transmission, and the machine are favorable prior to enabling the compression brakes. Once the conditions are met, the transmission ECM communicates a favorable status of the interlock control over the Cat Data Link to the engine ECM. The engine ECM then has direct control over the operation of the compression brakes. A problem with communications between the engine ECM and the transmission control will affect operation of the compression brake. The transmission control will restrict operation to the automatic mode during an active fault for the compression brake switch.Note: If a problem is suspected with the compression brake switch, refer to Troubleshooting, "Switch Circuits - Test" for troubleshooting information.Perform this procedure under conditions that are identical to the conditions that exist when the problem occurs. Typically, problems with the compression brake solenoids occur when the engine is warmed up and/or when the engine is under vibration (heavy loads)."Compression Brake Solenoid Override"The "Compression Brake Low/High Override" and the "Compression Brake Med/High Override" are diagnostic overrides that are available in Cat® 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 solenoid when the overrides are active. The overrides must be activated and then deactivated before the ECM will detect an open circuit.Note: The engine speed must be zero before the overrides will function.Note: All the retarder solenoids share a single return circuit. A short circuit or an open circuit in the return wire for the retarder solenoids will cause a problem with all the solenoids.
Illustration 1 g01199118
Location of the compression brake solenoid (typical example)
Illustration 2 g06297518
Schematic for the compression brake circuit
Electrical shock hazard. The electronic unit injector system uses 90-120 volts.
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, 2534-5, 2535-5, 1072-5 or a 1073-5 diagnostic code is active currently. 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, 2534-6, 2535-6, 1072-6 or a 1073-6 diagnostic code is active currently.
Proceed to Test Step 4.
2. Create a Short Between the Wires of the Suspect Compression Brake Solenoid at the Valve Cover Connector
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 scr