CB64B, CB66B and CB68B Asphalt Compactors Machine Electronic Control System Caterpillar

Machine Steer not Responding Properly

Usage:

SPN 2923 - Status of Steering Axle

The purpose of the uncommanded movement detection system is to stop the steering system if motion is detected without a command for a duration in time. This feature will also stop the machine if the motion is opposite of the commanded direction for a specified amount of time. This logic will stop machine movement under the following conditions:

The actual steering detected is beyond the tested acceptable rate over a continuous period of 300 ms.
The actual steering detected is in the wrong direction while steering for a continuous period of 300 ms.
Steer detected greater than 5° with no command for steer from the Front (steer) or Rear (offset) sensor.

If the Machine ECM detects UCMD, the system generates a Level 3 fault. An active UCMD will disable all propel, and vibe system functions. Propel command will go to zero and the parking brake and two-speed solenoids will be de-energized, causing the parking brake to be applied.

The Machine ECM monitors input signals from the front and rear Steer Sensors to determine the actual steer speed and direction. Contact A of each Steer Sensor receives 12 volt power. Each Steer Sensor provides a PWM signal to the Machine ECM from contact B.

The key switch must be cycled before the Diagnostic Code will be cleared and the machine will be allowed to operate.

The engine must be operating with the Park Brake switch in the OFF position before a status of Steering Axle Fault can occur.

Hydraulic Schematic (Steering System)

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Illustration 1	g06027429
Steering Hydraulic System STRAIGHT TRAVEL (1) Steering manifold (2) Steering priority valve (3) Shuttle valve (4) Flow control valve (5) Main relief valve (6) Counterbalance valves (7) Steering cylinder (8) Warm-up valve (9) Filter (10) From steering charge pump (11) Steering shunt valve (12) To charge filter inlet (13) Steering control valve (14) Shuttle valve

Causes for Steering Uncommanded Movement Detected (UCMD)

Air trapped in the Steer Cylinder, Valve, or Steer Lines. - Steer current calibration may be incorrect and can cause the 2923 Fault due to irregular or erratic operation.
Hydraulic Temp not to operating temperature and bypassed during Steer Current Calibration. - Steering may react irregular or erratic when hydraulic oil and components reach normal operating temperature.
Contamination in Steering Valve – Machine may steer unexpectedly at the Steer or Offset cylinder.
Hitch or Steer Cylinder worn – Creates unwanted movement between frames or steer cylinder and frame.
Loose, Bent or deformed steer sensor hardware – Incorrect movement in degrees and duty cycle may be reported to the ECM.
Steer Cylinder has internal leakage - Machine may not steer as expected.
Steer Calibration performed with machine on soft surface. - Steering may react irregular or erratic when turning slowly.

Diagnostic Trouble Code Procedure

Troubleshooting for SPN 2923 Codes

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Table 1
Steering Uncommanded Troubleshooting
Troubleshooting Test Steps	Results
1. Is there an active 2923-0 or 2923-7 Uncommanded Steer Fault?	YES - There is an active Uncommanded Steer Fault. Proceed to Test Step 2. NO - There is NOT an active Uncommanded Steer Fault. Proceed to Test Step 3.
2. Clear the 2923-0 or 2923-7 Fault. A. Set the Park Brake Switch to ON. B. Turn the keyswitch to the OFF Position. C. Wait 3 seconds. D. Start the engine. E. Did the Fault clear?	YES - The fault cleared. Proceed to Test Step 3. NO - The 2923 Fault remains active. Check the operation of the brake switch. Repair: If the machine steers uncommanded with the parking brake applied, repair or replace the steer valve.
3. Is there an active Steer Sensor Diagnostic Code?	YES - Follow the Diagnostic Code troubleshooting procedure. NO - Proceed to Test Step 4.
4. Is there an active Data Link Diagnostic Code?	YES - Follow the Diagnostic Code troubleshooting procedure. NO - Proceed to Test Step 5.
5. Check For Stationary Faults. A. With the engine started, set the Park Brake Switch to OFF. B. Wait 20 - 30 seconds. C. does a new 2923 fault occur with the steering wheel stationary?	YES - Shut off the engine. Remove the Front (steer) and Rear (Offset) CW and CCW solenoids from the steer valve. The harness must remain attached to the solenoids. Repeat this step. If the 2923 fault occurs with the solenoids removed. Repair: Repair or replace the Steer Valve. Note: The Left and Right Steer Valve components may be swapped to aid in isolating the faulty valve. NO - Proceed to Test Step 6.
6. Check The Steer Operation. A. With the engine ON and the Park Brake Switch set to OFF, Steer the machine to the Left 10° - 15° and wait 10 seconds. B. Steer the machine to the Right 10° - 15° and wait 10 seconds. C. Does the machine continue to steer in either direction? Is a 2923 fault set?	YES - The fault occurs during or after steering in either direction. Proceed to Test Step 9. NO - Proceed to Test Step 7.
7. Check the machine while propelling on uneven terrain. A. Operate the machine over uneven terrain (or a small step with a difference of approximately 12 mm (0.47 inch). B. Does a new 2923 fault occur?	YES - Check the machine hitch or steer cylinder hardware for wear. Repair: Repair as necessary. NO - Proceed to Test Step 8.
8. Use Plus+1 Service Tool for Caterpillar. A. Engine is running. Park Brake is OFF. B. Use the Plus+1 Service Tool for Caterpillar (P1STC) to view the steer solenoid current to each solenoid. C. The steering wheel is stationary. Is the current approximately 50 mA for the Front CW and CCW steer solenoid?	YES - Monitor the following for incremental or decremental operation: - the steering command - steer solenoid currents - degrees of steering position Compare the left and right steer signals and currents. Are any values erratic or inconsistent with each other. Check the component, harness, or hardware from which the signal originates. NO - Proceed to Test Step 10.
9. Swap the Counterbalance Valves A. Set the Park Brake switch to OFF position. Turn the engine start switch to OFF position. B. Swap the locations of the steer valve counterbalance valves. C. Does the uncommanded steer fault occur by steering in the opposite direction?	YES - The counterbalance valve is malfunctioning. Repair: Replace the Counterbalance Valve. NO - Proceed to Test Step 10.
10. Calibrate the Steering Valve. A. The hydraulic oil needs to be above 43° C (109° F). B. Perform the "Steering Valve Current Minimum - Calibrate" procedure.	Refer to Steering Valve Current Minimum - Calibrate in UENR6299Testing and Adjusting, "CB64B, CB66B, and CB68B Asphalt Compactors Machine Systems"