T450 Skid Steer Lift Arms & Tilt Lock Up



New member
Jun 7, 2021
Bobcat T450 Compact Tracked Loader
The lift arms and tilt lock up on my 2015 Compact Tracked Loader after 15 - 30 minutes of operation while using a bucket or auger attachment. The only fault code displayed is M3507 (Hydraulic fan open circuit), usually displaying after 2 - 5 minutes of operation. The fan is turning and the engine temperature is normal so I don't believe this is a real fault. The lift arms can be lowered using the bypass valve, but they still won't lift or tilt until a reset occurs, usually which takes an overnight cooldown. Occasionally, I've been able to reset by raising and lowering the seat bar, or by turning the key ON & OFF 3 times, but that doesn't always work (usually doesn't). I've replaced the Control Valve Poppet Valve, the BICS Solenoid, the battery & the battery ground cable. The Bobcat dealer replaced the ACS Controller, but the lockup returned, again after 15 minutes of operation. Typically the red LIFT AND TILT Valve light flashes on the display when the lock up occurs. The drive system function is not affected.

Any ideas of what is going on? I'm surprised no additional fault codes are displayed.

Many thanks for any help!!


Elite Member
Jun 25, 2010
Cumberland Plateau, TN
Bobcat CT225
Cannot say why you are not seeing a fault code but when the valve light is flashing means the main controller is detecting a fault. The number of flashings between a slight pause. A steady flash (1 blink then pause) indicates open circuit in the power output wire. Keep in mind there are 2 power wires, a pull circuit that is on only momentary activated through a relay that pulls the valve stem open then turns off. 2 power is the "hold" coil circuit which is lower lower voltage, lower amp that holds stem open while operating. The light flashes are reading/referring to this circuit. Possible problem for this is corroded connection or partially broken wire that works when cold but resistance gets too high after a time so voltage to the hold coil is too low or none.
Two blinks then pause indicate "short to battery power" ie: is reading full battery voltage in the circuit. The controller has an internal resistor for that hold circuit output to reduce voltage to a level that maintains the magnetic field but low enough to avoid excessive heat build up during long hours of operation. Most frequent cause of this is alternator over charging or loose corroded ground connection.
Three blinks then pause indicate either voltage output short to ground or no ground connection.