Volvo L70G Loader Stalls and Hydraulic Delay Linked to Priority Valve and Steering Circuit

[MikePhua]

Quick answer
A Volvo L70G loader experiencing cold-start hydraulic delay and engine stalling during warm operation likely suffers from steering priority valve malfunction or internal hydraulic blockage. Steering input temporarily restores function, suggesting the loader’s hydraulic flow is being misrouted or restricted until the steering circuit is activated.
Volvo L70G background and hydraulic architecture
The Volvo L70G is a mid-sized wheel loader introduced in the early 2010s, part of Volvo Construction Equipment’s G-series lineup. It features:

• A 6-liter Volvo D6H diesel engine
  
• Load-sensing hydraulic system with variable displacement pump
  
• Electrohydraulic controls for boom and bucket
  
• Priority valve for steering circuit
  
• Closed-center hydraulic architecture
  

The L70G was designed for fuel efficiency, responsive control, and low emissions. Over 10,000 units have been sold globally, with strong adoption in municipal, quarry, and snow removal fleets.
Symptoms and operational behavior
In this case, the loader exhibits two distinct issues:

• Cold-start delay in boom raise and bucket tilt: Functions are sluggish or nonresponsive until the steering wheel is turned repeatedly
  
• Warm-engine stalling during idle: The engine begins to stall unless the steering wheel is moved, which restores operation
  

These symptoms suggest that hydraulic flow is being diverted or blocked until steering input triggers a change in valve position or pump demand.
Steering priority valve and load-sensing logic
The L70G uses a priority valve to ensure steering always receives hydraulic flow, even under full load. This valve is part of the load-sensing circuit and interacts with the main hydraulic pump via pressure feedback.
If the priority valve sticks or fails to reset:

• Boom and bucket functions may be starved of flow
  
• The pump may remain in low-displacement mode
  
• Steering input may trigger valve movement, restoring flow
  

Additionally, if the load-sensing signal line is blocked or leaking, the pump may not respond to demand, causing engine stall due to unregulated flow or pressure spikes.
Diagnostic recommendations
To isolate the fault:

• Inspect the steering priority valve: Remove and clean spool, check for scoring or debris
  
• Test load-sensing signal pressure: Use a gauge at the pump control port
  
• Check hydraulic filters and screens: Clogged filters can mimic valve failure
  
• Verify pump displacement control: Ensure pump responds to joystick input
  
• Scan for fault codes: Use Volvo’s VCADS or Tech Tool diagnostic software
  

One technician reported a similar issue on a Volvo L90G where the priority valve spool was sticking due to cold-weather contamination. After cleaning and replacing the O-rings, full function was restored.
Preventive measures and long-term solutions

• Use winter-grade hydraulic oil in cold climates to reduce viscosity-related sticking
  
• Replace hydraulic filters annually, especially in high-dust environments
  
• Flush the system after long storage periods
  
• Train operators to avoid prolonged idling without hydraulic engagement
  

If the valve is damaged or worn, replacement is recommended. Volvo offers updated valve assemblies with improved sealing and spool tolerances.
Conclusion
The Volvo L70G’s hydraulic delay and engine stalling are likely caused by a malfunctioning steering priority valve or disrupted load-sensing feedback. Steering input temporarily restores flow, pointing to valve spool sticking or pump control issues. With targeted diagnostics and valve inspection, the loader can be returned to full operational reliability.