PISTON-CONTROL 2055007 - Caterpillar

Illustration 1 g03029438
Schematic for the compression brake circuit
Probable Causes
Codes
Short circuit
Open circuitRecommended Actions
Table 2
Troubleshooting Test Steps Values Results
1. Check for Codes
A. Connect Cat® Electronic Technician (ET) to the service tool connector.
B. Turn the keyswitch to ON.
C. Access the diagnostic overrides under the "Diagnostics" menu.
D. Start the "Compression Brake Low/High Override".
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. Record any active diagnostic codes.
G. Start the "Compression Brake Med/High Override".
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. Record any active diagnostic codes.
Codes
Result: A 791-5, or 792-5 diagnostic code is active.
Proceed to Test Step 2.
Result: A 791-6, or 792-6 diagnostic code is active.
Proceed to Test Step 4.
2. Create a Short Between the Wires of the Suspect Compression Brake Solenoid at the Valve Cover Connector
Note: To troubleshoot a 791-5 diagnostic code, use the "Compression Brake Low/High Override" in Cat ET. To troubleshoot a 792-5 diagnostic code, use the "Compression Brake Med/High Override" in Cat ET.
A. Turn the keyswitch to OFF.
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 ON.
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 in Cat ET. Record any active diagnostic codes.
I. Turn the keyswitch to OFF. Remove the jumper wire.
Note: 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
Result: A 791-6, or 792-6 diagnostic code is active. The harness wiring is OK.
Proceed to Test Step 3.
Result: A 791-5, or 792-5 diagnostic code is active.
Repair: Repair the harness or replace the harness.
If the problem is not resolved, proceed to Test Step 3.
3. Create a Short Circuit at the Compression Brake Solenoid
Note: 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.
Note: To troubleshoot a 791-5 diagnostic code, use the "Compression Brake Low/High Override" on Cat ET. To troubleshoot a 792-5 diagnostic code, use the "Compression Brake Med/High Override" on Cat ET.
A. Turn the keyswitch to OFF.
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