Caterpillar 950G Transmission Shifting Problems

[MikePhua]

Issue Summary
Owners of the 2001 Caterpillar 950G wheel loader report an issue with the automatic transmission shifting, specifically that the machine will shift from 1st gear to 2nd gear but immediately pops back to 1st gear. In manual mode, however, the transmission shifts correctly. Additionally, when cycling through gear selectors from 1 to 4, the display fails to show 2nd gear even though 3rd and 4th gears display properly.
Transmission Overview

• The Caterpillar 950G uses an electronically controlled, planetary powershift transmission.
  
• It features four forward and four reverse gears with automatic shifting and manual override options.
  
• Transmission operation depends on clutch pack engagement controlled hydraulically via electronic signals.
  
• The transmission system includes sensors and displays that indicate engaged gear positions to the operator.
  
• A torque converter assists with smooth power delivery and gear transitions.
  

Possible Causes of the Problem

• Faulty or Misreading Gear Position Sensor: The sensor responsible for detecting and displaying 2nd gear may be faulty, causing the display issue and potentially impacting automatic shift logic.
  
• Hydraulic Control Valve Malfunction: The valve controlling shift to 2nd gear may be sticking or leaking internally, preventing sustained engagement.
  
• Programmable Transmission Controller Fault: Software or electronic control module error causing incorrect shift commands or sensor readings.
  
• Mechanical Clutch Pack Wear or Damage: The 2nd gear clutch pack may be worn or damaged leading to slipping under automatic control but manageable under manual control.
  
• Wiring or Connector Issues: Damaged or intermittent electrical wiring could affect shift solenoid control or sensor signals.
  

Diagnostic Recommendations

• Perform electronic diagnostic scans focusing on transmission codes and sensor data.
  
• Inspect gear position sensors and confirm accurate gear detection via manual testing.
  
• Check hydraulic pressure at shift valves and confirm fluid cleanliness and levels.
  
• Inspect valve block functioning for proper actuation of 2nd gear clutch.
  
• Review transmission controller settings and update or reload software if available.
  
• Conduct mechanical inspection of the clutch pack if hydraulic and electronic systems check out.
  

Terminology

• Powershift Transmission: A transmission allowing gear changes without interrupting power flow.
  
• Clutch Pack: A set of friction plates that engage gears inside the transmission.
  
• Torque Converter: Fluid coupling between engine and transmission for smooth power transfer.
  
• Gear Position Sensor: Device detecting which gear is currently engaged and communicating with the display/controller.
  
• Shift Solenoid: Electromechanical valve controlling hydraulic pressure to engage specific gears.
  

Real-World Insights
Operators facing similar issues highlight the importance of electronic diagnostics and often find sensor replacement or transmission controller software updates resolve display and shifting anomalies. Hydraulic component cleanliness and clutch pack condition are also crucial for optimal auto shift performance.
Conclusion
950G automatic transmission shift problems related to 2nd gear typically arise from sensor failures, valve control issues, or electronic control faults. Manual shifting working fine suggests mechanical components remain functional but control systems require targeted diagnostics. Resolving sensor and hydraulic valve issues combined with software checks restores reliable auto shifting and accurate gear indication, preserving the machine's productivity and operator confidence.