TB 035 Pilot Control Valve Solenoid – Troubleshooting Guide

[MikePhua]

What’s Going On
The TB 035 (Takeuchi mini‑excavator) has a problem where the boom, stick, or other pilot-controlled hydraulic functions don’t respond after the machine sits idle. The fuse on the control panel checks out fine. Also, the limit switch under the control handle (the safety interlock) tests correctly with a meter. That points to a likely failure in the pilot‑control valve’s solenoid — the small electromagnet that shifts the pilot valve.
Why the Solenoid Matters

• The pilot control valve directs hydraulic pilot flow, which then influences the main control spool to move cylinders (boom, stick, etc.).
  
• If the solenoid that actuates this valve doesn’t energize, no pilot flow means no motion, even if hydraulics and levers are otherwise okay.
  
• When the machine has sat for a while, voltage or wiring issues may prevent the solenoid from triggering, so even though the safety switch is good, nothing happens.
  

Key Diagnostic Steps

1. Check for 12V at the Solenoid
   • With the key on and attempt to move the control, use a multimeter to test whether the solenoid coil is getting power.
     
   • No voltage = likely wiring, interlock switch, or fuse issue; voltage present but no action = bad coil or stuck pilot spool.
     
2. Inspect Wiring and Connectors
   • Look for loose, corroded, or damaged plugs on the solenoid.
     
   • Make sure the ground circuit is solid — a bad ground can prevent the solenoid from pulling in.
     
   • Clean connectors and apply dielectric grease to improve contact reliability.
     
3. Test or Replace the Solenoid
   • If voltage is correct and the solenoid doesn’t activate, you may need to swap it out.
     
   • Consider cycling power several times to test whether the solenoid is sticking.
     
4. Check Hydraulic Oil
   • Very contaminated or aerated oil in the pilot circuit can prevent the valve spool from shifting even if the solenoid is working.
     
   • If the oil is dark, metallic, or milky, it might be time to service the hydraulic reservoir, flush pilot lines, or change filters.
     

Possible Solutions

• Replace the pilot-control solenoid with a high-quality unit if it's not actuating.
  
• Clean and tighten all wiring connections related to the solenoid and control handle.
  
• Ensure that the machine’s interlock mechanism (limit switch) is properly adjusted and functioning, so it allows correct solenoid triggering.
  
• If oil contamination is detected, flush the system, replace pilot filters, and bleed the pilot circuit thoroughly.
  

Replacement Part Examples
Here are some solenoids and pilot valves you might consider (verify compatibility with your TB 035):

• Takeuchi TB035 Hydraulic Valve #1357765 — direct-fit hydraulic valve, may include or require pilot valve replacement.
  
• Aftermarket Takeuchi Stop / Pilot Solenoid — replacement solenoid designed for certain Takeuchi models.
  
• Excavator Proportional Pilot Solenoid Valve — more universal or proportional type, potential fallback if OEM is unavailable.
  

Preventive Advice

• Check the solenoid coil resistance periodically to catch early degradation.
  
• Include pilot-circuit inspections in regular maintenance: look for oil quality, leaks, or wiring aging.
  
• During winter or storage, perform power-up checks of the solenoid before operational use.