Bobcat Auxiliary Hydraulics Not Working? Step-by-Step Electrical vs. Mechanical Troubleshooting 

If your Bobcat's auxiliary hydraulics quit and the grapple won't open or the auger won't spin, the root cause is either electrical or mechanical-and a few tests with a multimeter and a screwdriver will tell you which one before you spend a dollar on parts. A blown $5 fuse and a $2,500 control valve replacement both produce the same symptom: no flow at the quick couplers. The diagnostic path in this guide separates the two.

Before You Start: Confirm the Basics

Before tracing wires or pulling solenoids, rule out two common non-faults. The Bobcat Interlock Control System (BICS) must be satisfied-operator in the seat, restraint bar fully lowered, all indicator lights green. If any condition is unmet, the machine disables the auxiliary circuit entirely. Next, check the quick couplers at the boom. Residual pressure in the attachment hoses can prevent full engagement. Bleed the pressure, disconnect and reconnect the lines, and try again. These two checks take 60 seconds and account for a surprising number of calls that never needed a wrench.

The auxiliary hydraulic circuit on a Bobcat is a chain of electrical and mechanical components working in sequence: a fuse feeds a controller, the controller energizes solenoid coils, those coils shift valve spools, and oil flows to the quick couplers. A failure anywhere along that chain kills the output. The lift arms and bucket typically still work fine-the aux circuit is a separate electrical path, which is exactly why it can be diagnosed independently.

How the Bobcat Auxiliary Hydraulic Circuit Works

Understanding the signal path makes diagnosis logical instead of random. The operator presses the auxiliary mode button on the left console to activate the circuit. When the thumb switch on the right joystick is actuated, the signal travels to an electronic controller. In C-series and G-series machines (753, 763, 863), this is the Pulse Width Modulator (PWM)-a sealed box mounted to the left side of the loader frame under the seat. In M-series and R-series machines (S510, S550, T590, T650, and newer), the main controller or gateway module handles this function over a CAN bus network.

The controller sends current to solenoid coils mounted on the main control valve block beneath the cab. Those coils generate a magnetic field that pulls a stem, shifting a spool inside the valve body and redirecting hydraulic oil to the quick couplers on the boom. Two solenoids handle directional flow-base end and rod end-allowing the operator to run an attachment in both directions.

One detail trips up a lot of operators doing their own electrical diagnosis: the Bobcat PWM controller does not send 12 volts to the aux solenoid coils. It sends a proportional signal that ranges from 0.0 to 6.0 volts, varying with thumb switch position. Applying 12V directly to a PWM-controlled coil will burn it out.

Tip from the Skidsteers.com team: Before you start pulling wires, note whether the LED indicators on the dash aux switch illuminate when you press the button. If neither LED lights up, the problem is almost certainly upstream of the solenoids-in the fuse, controller, or switch wiring. If the LEDs light normally but nothing happens at the couplers, the issue is likely at the solenoid or valve level. That single observation cuts the diagnostic tree in half.

Electrical Troubleshooting: From the Bobcat Auxiliary Hydraulic Fuse to the Solenoid

Electrical faults account for the majority of auxiliary hydraulic failures, and they follow a predictable path. Work through these steps in order-each one rules out a component before you move to the next.

Check the Fuse

The auxiliary circuit has a dedicated fuse, typically labeled PWM in C/G-series machines or ACD (Attachment Control Device) in M-series and newer. On older machines, it is near the battery in the engine compartment or on a fuse block under the seat.

A blown PWM fuse is the single most common electrical cause of Bobcat auxiliary hydraulics not working. Fuses can look intact visually but fail internally-put a multimeter across the pins and check for continuity rather than eyeballing it. Forum threads on this problem consistently end with operators replacing a fuse that "looked fine" but had no continuity pin to pin. A replacement costs under $5. If the new fuse blows immediately, there is a short downstream-likely in the wiring harness or a solenoid coil-that needs to be found before replacing the fuse again.

Test the Bobcat Auxiliary Hydraulic Switch and Wiring

If the fuse is good but the LEDs on the auxiliary switch do not light, the next suspect is the switch itself or the wiring between the switch and the controller.

The most common failure point is inside the right control handle, where wires flex constantly with every joystick movement. Over thousands of hours, insulation wears through and conductors break or short against the frame. Unplug the harness connector at the joystick and test for continuity through each wire. A broken conductor here can cause intermittent or total loss of the auxiliary function.

The aux switch itself can be tested by measuring voltage on its output terminal while pressing the button (ignition on, engine running). If power goes in but does not come out, the switch is faulty. Replacement cost is around $125 for the OEM part, though some operators have salvaged switches by resoldering corroded LED leads-a $1.50 fix worth attempting before ordering the full assembly.

Test the Bobcat PWM Controller Auxiliary Hydraulics

If the fuse and switch check out but the LEDs still will not light-or they light but no voltage reaches the solenoid coils-the PWM controller is next. On C/G-series machines, the PWM box is the sealed module on the left side of the loader frame under the seat.

To test it, measure voltage at the output pins going to the solenoids while someone activates the aux function from the cab. You should see 0.0 to 6.0V varying with thumb switch position. Zero volts at the output with confirmed power at the input means the module has failed. The PWM box is a potted (resin-sealed) unit and cannot be repaired-replacement runs around $600 on C-series machines.

In M-series and R-series machines, the main controller reports faults as digital codes on the instrument panel: H2607 (open circuit on front base solenoid output), H2707 (front rod solenoid open circuit), H2905-H2907 (high-flow solenoid faults), and H1221/H1222 (thumb switch out of range). These codes point directly to the failed component, making diagnosis significantly faster than on older machines.

Bobcat Aux Hydraulic Solenoid Troubleshooting

If voltage reaches the solenoid coils but nothing happens, test the coils themselves. Disconnect the electrical connector from the solenoid and measure resistance across the coil pins with the multimeter set to ohms.

A healthy coil on a PWM-controlled Bobcat should read between 1 and 8 ohms, depending on the series-older C-series coils typically read 1-5 ohms, while some F/G-series coils run 5-8 ohms. An "OL" (open line/infinite resistance) reading means the coil winding is broken internally and the coil is dead. A reading near zero ohms indicates an internal short, which will blow the fuse as soon as the circuit is energized. Either condition requires coil replacement. A new coil runs $20-$150 depending on whether you buy OEM or aftermarket.

To locate the solenoids, lift and lock the cab (ROPS). The main control valve block is behind the throttle linkage, centered beneath the seat. The auxiliary solenoids are cylindrical coils threaded onto metal stems on the auxiliary section of the valve block-the section from which hydraulic lines run to the quick couplers on the boom. Each coil is secured with a 3/4-inch cap nut. Two coils handle directional flow, and machines with high-flow capability will have a third.

Tip from the Skidsteers.com team: Here is a fast field test that does not require a multimeter. Remove the solenoid coil from its stem (cap nut off, slide the coil up), insert a steel screwdriver shaft into the center of the coil, and have someone activate the aux function from the cab. If the coil generates a magnetic field, you will feel the screwdriver pulled strongly into the coil. That confirms the entire electrical chain-fuse, controller, wiring, and coil-is working. If the magnet pulls hard but no oil flows, the problem is mechanical: the stem or spool inside the valve is stuck. This "screwdriver test" is the fastest way to split the diagnosis between electrical and mechanical.

Mechanical Troubleshooting: Bobcat Hydraulic Control Valve Problems and Beyond

When the electrical path checks out-voltage at the coil, good resistance, strong magnetic pull-but auxiliary hydraulics still produce no flow or pressure, the fault is mechanical. The three most common culprits are a stuck valve spool, a failing relief valve, and blocked quick couplers.

Stuck Spool or Stem

A solenoid coil can generate all the magnetism in the world, but if the stem it pulls is seized inside the valve body, nothing moves. This is the most common mechanical cause of Bobcat aux hydraulics producing no pressure despite a fully functional electrical system.

The usual causes are contamination (dirt, metal shavings, or seal fragments lodged in the bore), varnish deposits from overheated hydraulic oil, and simple disuse-machines that sat for years without running the aux circuit develop corrosion that bonds stems in place. Varnish-related sticking is often intermittent: the spool moves when cold but binds after warmup as thermal expansion tightens already-narrowed tolerances.

To confirm, remove the coil and try to move the stem by hand or with pliers. A free stem should slide smoothly. If it is locked, the stem needs to be removed, cleaned, and reinstalled-or the spool assembly replaced if the bore is scored. Professional valve rebuild runs $300-$700. A new control valve from the dealer can exceed $2,500.

Relief Valve Issues

If the aux circuit activates (you can hear oil flowing or the hoses pressurize briefly) but there is no real power at the attachment, the auxiliary relief valve may be opening at too low a pressure. Factory settings for auxiliary relief pressure vary by model: 2,550-2,600 PSI on 753-series machines, 2,700-2,750 PSI on 853-series, and 3,450-3,550 PSI on M-series models.

Testing requires a hydraulic pressure gauge connected to the quick couplers. Run the engine at full RPM, activate the aux circuit against a dead-headed load, and read the peak pressure. If it falls below spec, the relief valve spring may be weak or the valve seat contaminated. The main relief valve is in the right rear area of the control valve block. Remove it, inspect the O-rings and backup washers (a cracked O-ring is the most common cause of internal pressure loss), clean the seat, and adjust with the setscrew-one full turn changes pressure by roughly 390-490 PSI depending on the model.

Quick Coupler Problems

If both couplers are not fully clicked into the attachment fittings, oil will not flow. Residual pressure can prevent full engagement, and dirt packed into the coupler face can block the poppet valve from opening. Disconnect both lines, clean the faces, bleed pressure, and reconnect firmly until the locking collar snaps.

Intermittent Failures: When Bobcat Aux Hydraulics Work, Then Quit

Aux hydraulics that work for 10-15 minutes and then stop-often recovering overnight-have three possible causes, and isolating the right one depends on what you observe at the moment of failure.

If the solenoid coil still produces a strong magnetic pull at the moment the system quits, the problem is mechanical-thermal expansion of a contaminated or varnish-coated spool binding as oil heats up. The system works cold, fails warm, recovers overnight. A valve disassembly and thorough cleaning is the fix.

If the magnetic pull disappears when the system stops, the coil is failing under heat. Measure resistance immediately at failure-OL (open) confirms the winding is fracturing internally, opening when hot and closing when cold. Replace the coil.

If the dash LEDs begin flashing in a diagnostic pattern when the system drops out, the PWM controller is shutting down the circuit-either from overcurrent caused by a degraded coil or from internal overheating. Alternating flashes of the Momentary and Detent LEDs typically indicate a switch failure; a single flashing LED points to a specific solenoid circuit fault.

Standard Flow vs. High Flow: What Changes in the Aux Circuit

Machines equipped with high flow add a dedicated Hi-Flow on/off switch on the left instrument panel, a third solenoid on the control valve block, and a second gear pump whose output combines with the main pump when activated.

The key electrical difference: base-end and rod-end solenoids receive variable PWM voltage (0.0-6.0V) for proportional speed control, while the high-flow solenoid operates as a simple on/off valve at near-full system voltage-approximately 11.5-12.0V when energized.

If standard-flow aux works but high flow will not engage, check the Hi-Flow switch on the dash, then test for voltage at the high-flow solenoid connector with the switch on and aux active. No voltage points to the switch or wiring. Voltage present but no additional flow suggests the high-flow solenoid or diverter valve has failed mechanically.

Tip from the Skidsteers.com team: If you have just bought a used Bobcat and the previous owner never ran high-flow attachments, do not be surprised if the high-flow function does not respond at all. The diverter solenoid and its spool are the most likely components to seize from disuse. Cycle the high-flow function regularly-even without an attachment connected-to keep that valve moving. Five minutes a month prevents a stuck spool that costs hours to free.

Repair Cost Breakdown: What Bobcat Auxiliary Hydraulic Repairs Actually Cost

The spread between a minor electrical fix and a major mechanical rebuild is enormous. A blown PWM fuse runs under $5. The auxiliary LED switch assembly costs around $125, though operators have repaired corroded LED connections for under $2. A solenoid coil ranges from $20 (aftermarket) to $150 (OEM). Wiring harness repairs run $100-$300 in labor. The PWM controller module is approximately $600 on C-series machines and is a sealed, non-repairable unit. A control valve rebuild runs $300-$700, and a complete new valve assembly from a Bobcat dealer can exceed $2,500.

The further downstream the problem-from fuse to controller to valve-the more expensive the fix. Replacing a $600 PWM box when the problem was a $5 fuse, or pulling a $2,500 valve when a $65 solenoid coil was the culprit, is money that did not need to be spent.

Once the auxiliary circuit is back in working order and delivering clean, consistent flow, it is worth considering what you are asking it to power. Attachments that depend on the aux circuit-grapples, augers, brush cutters, trenchers-need steady pressure and reliable flow to perform the way they were designed to. For a full selection of skid steer attachments built for the aux circuits on Bobcat and other machines-including grapples, augers, and brush cutters with the compatibility and flow specs to match-Skidsteers.com carries the lineup.