Electrical or Hydraulic? How to Diagnose a Scissor Lift Problem Before Replacing Parts

One of the most common troubleshooting mistakes on a scissor lift is deciding too early that a problem is either “electrical” or “hydraulic.”

In reality, the two systems work together. The electrical control system tells the machine what to do, while the hydraulic system creates the physical movement for functions such as lifting, lowering, and in some designs, steering.

That means the same visible symptom can come from either side.

A platform that will not raise, for example, may have no hydraulic pressure because the pump is worn. But it may also have no hydraulic pressure because the pump motor never received an electrical command.

The most useful diagnostic question is therefore not simply “Is this electrical or hydraulic?”

A better question is:

Where does the correct command stop producing the expected response?

This guide explains how to separate electrical faults from hydraulic faults by following the machine's command path instead of replacing parts based on symptoms alone.

Safety note: Aerial work platform diagnosis, electrical testing, hydraulic testing, and repair should be performed by qualified personnel using the correct manufacturer service documentation and safety procedures.

Start With the Command, Not the Component

Every machine function begins with some form of operator request.

For example, when the operator commands lift, the sequence may involve:

Joystick or lift switch input
Enable or safety conditions
Control box or controller
Electrical output to a contactor, motor, solenoid, or valve
Hydraulic pump operation
Hydraulic flow and pressure
Valve movement
Cylinder movement

If the machine fails to perform the requested function, the diagnostic goal is to determine how far this sequence progressed before the response disappeared.

This approach is much more useful than immediately replacing the joystick, control box, hydraulic pump, or valve.

If the Pump Motor Never Runs, Stay on the Electrical Side First

When a lift command is given and the hydraulic pump motor does not run at all, the problem usually needs to be investigated on the electrical or control side before the hydraulic pump itself is condemned.

Possible areas include:

Battery supply
Emergency-stop circuit
Enable switch
Joystick or lift switch
Wiring and connectors
Fuse or circuit protection
Controller or PCB output
Contactor or relay
Pump motor electrical circuit

The pump cannot create hydraulic flow if the motor driving it never receives the command or power required to operate.

This is why a “won’t lift” symptom does not automatically justify replacing the hydraulic pump.

For a wider electrical-system diagnostic sequence, see our Aerial Lift Electrical Problems guide.

If the Pump Motor Runs but the Platform Does Not Move, Shift Toward Hydraulics

If the pump motor clearly runs when the lift command is requested, an important part of the electrical command path has already occurred.

At that point, the next questions are hydraulic:

Is the pump producing flow?
Is adequate hydraulic pressure being developed?
Is the directional valve operating?
Is hydraulic oil reaching the lift cylinder?
Is a relief valve opening incorrectly?
Is there internal leakage?
Is the lift mechanism mechanically restricted?

This does not mean every upstream electrical component can be ignored, but the running pump motor is a strong clue that diagnosis should now move toward the hydraulic response.

If the machine's primary symptom is specifically failure to raise, see our Scissor Lift Won't Lift troubleshooting guide.

Use One Working Function to Eliminate Shared Components

A working machine function can be just as useful diagnostically as a failed one.

For example, if the hydraulic pump operates normally during one function but another hydraulic function does not work, the pump itself becomes less likely to be the root cause.

Likewise, if several control functions operate correctly from the same joystick or control station, shared power and communication components may already be partially proven.

Ask:

Which functions still work?
Which functions share the same pump?
Which functions share the same controller?
Which functions use different valves?
Which functions use the same joystick?

This comparison can help reduce the number of possible causes much faster than testing every component individually.

Compare Platform Controls With Ground Controls

Many scissor lifts allow certain functions to be operated from both platform and ground control stations.

This provides an extremely useful comparison.

If a function works correctly from the ground controls but fails from the platform controls, much of the downstream system is already capable of operating.

The diagnostic focus can then move toward:

Platform joystick or switch
Platform enable circuit
Platform control box
Platform wiring harness
Platform connectors

If the same function fails from both control stations, the fault is more likely to be located further downstream in a shared controller, output circuit, valve, motor, hydraulic component, or mechanical system.

Electrical Symptoms That Deserve Closer Attention

Some symptoms are more likely to point toward the electrical or control side of the machine.

Examples include:

No pump or motor command at all
Functions disappear when wiring or connectors move
Multiple functions stop at the same time
Operation returns after cycling the key or emergency stop
A function works from one control station but not another
The problem changes with vibration
Fault appears after a connector is disturbed
Controller or communication faults appear

These patterns suggest that the command may not be reaching the hydraulic or mechanical part of the system consistently.

If the machine stops unpredictably and then works again, see our Scissor Lift Stops Suddenly? guide.

Hydraulic Symptoms That Deserve Closer Attention

Other symptoms suggest that the electrical command may be present but the hydraulic response is weak or incorrect.

Examples include:

Pump motor runs but the platform does not rise
Platform lifts only with a light load
Hydraulic movement becomes very slow
Pump noise changes noticeably
Hydraulic fluid is low or contaminated
A valve receives a command but does not respond correctly
One hydraulic function is weak while electrical controls appear normal
Movement changes as hydraulic temperature changes

These symptoms justify moving deeper into hydraulic diagnosis.

For a broader hydraulic-system overview, see our Scissor Lift Hydraulic Failure Guide.

When Electrical and Hydraulic Faults Produce the Same Symptom

This is where misdiagnosis happens most often.

Example: Platform Will Not Lift

Possible electrical causes include:

Missing joystick command
Failed enable switch
Damaged wiring
Controller output failure
Pump contactor problem

Possible hydraulic causes include:

Worn pump
Valve problem
Low hydraulic fluid
Relief-valve issue
Internal cylinder leakage

Example: Platform Moves Slowly

Possible electrical causes include:

Low battery voltage
Poor high-current connection
Motor-control problem

Possible hydraulic causes include:

Restricted flow
Worn hydraulic pump
Valve restriction
Internal leakage

This overlap is why symptoms should be used to choose a diagnostic direction—not to identify a replacement part by themselves.

For slow movement specifically, see Why Is My Scissor Lift Moving Slowly?.

Use the Pump Motor as a Diagnostic Divider

For lift-related problems on many electric scissor lifts, the hydraulic pump motor provides a useful dividing point between electrical and hydraulic diagnosis.

A simple way to think about it is:

No pump motor response: stay upstream and investigate the electrical command and power path.

Pump motor runs: determine whether hydraulic flow, pressure, valve operation, and cylinder response are correct.

This is not a universal rule for every machine function, but it is a useful way to prevent premature hydraulic-pump replacement.

Use the Solenoid or Valve Command as Another Divider

Solenoid-operated valves provide another useful diagnostic checkpoint.

If the controller sends no command to the solenoid, the fault remains upstream in the controls, safety logic, wiring, or controller.

If the correct command reaches the solenoid but the valve does not respond, the diagnosis moves toward:

Solenoid coil
Valve spool
Hydraulic contamination
Valve body
Hydraulic flow path

This principle is especially useful for lowering, steering, and other hydraulically controlled functions.

What Does “Motor Runs but Nothing Moves” Usually Tell You?

This is one of the most useful troubleshooting observations.

If an electric motor is clearly operating but the commanded mechanical or hydraulic function does not occur, some of the electrical command path has already succeeded.

The next diagnostic step should focus on whether the motor is producing useful mechanical output and whether the downstream hydraulic or mechanical system responds.

For a hydraulic pump, that means checking flow, pressure, coupling, valve operation, hydraulic fluid, and downstream components rather than immediately replacing the control box.

What Does “Nothing Happens at All” Usually Tell You?

If no contactor activates, no pump motor runs, no valve is energized, and no output device responds, start much earlier in the command chain.

Check:

Battery supply
Main power
Emergency stops
Control enable
Operator input
Safety conditions
Wiring
Connectors
Controller inputs and outputs

A completely silent machine function is usually a stronger reason to investigate electrical permission and command than to begin with the hydraulic component.

How to Use Fault Codes Without Letting Them Mislead You

Fault codes can help identify the affected circuit or system, but they should not automatically be interpreted as proof that the named component has failed.

A controller may report a circuit-related fault because of:

Open wiring
Poor connector contact
Missing supply voltage
Ground problems
Communication failure
The actual component itself

Use fault information together with wiring diagrams, circuit testing, and the machine's actual behavior.

A fault code should guide the diagnosis, not replace it.

When Should You Test Hydraulic Pressure?

Hydraulic pressure testing becomes more useful after the electrical command and pump operation have already been confirmed.

Pressure testing can help distinguish between:

Insufficient pump output
Relief-valve problems
Valve leakage
Internal cylinder leakage
Other hydraulic pressure loss

Pressure testing should always follow the machine manufacturer's procedure and use appropriate equipment.

Testing pressure before confirming that the pump is actually being commanded correctly can waste time and lead to misleading conclusions.

When Should You Test the Joystick or Control Box?

Control-side testing becomes especially important when:

The pump motor never receives a command
One control station works while another does not
A function is intermittent
Several functions controlled by the same assembly fail
The command signal disappears before reaching the output device

If testing confirms that the control component itself is faulty, replacement identification should still include the OEM part number, machine model, serial number, connector layout, and control configuration.

When Should You Suspect the Hydraulic Pump?

A hydraulic pump becomes a stronger suspect when:

The pump motor runs correctly
The mechanical connection to the pump is intact
Hydraulic fluid supply is correct
The appropriate valve path is available
Pressure or flow remains below specification

Before purchasing a replacement pump, verify the technical specifications rather than matching appearance alone.

Our Aerial Lift Hydraulic Pump Replacement Guide covers OEM number, voltage, ports, flow, pressure, mounting, shaft and rotation checks in more detail.

When Should You Suspect the Control Board?

A controller or PCB becomes a stronger suspect when its required power, ground, inputs, safety conditions, communication and external wiring have been verified but the expected output remains missing or incorrect.

Do not replace an electronic board solely because several functions stop working.

Shared power, wiring, connectors, or communication faults can produce the same symptom.

If diagnosis actually points to the PCB, see our Aerial Lift Control Board Replacement Guide before ordering.

A Practical Electrical vs Hydraulic Diagnostic Decision

When the machine has a movement-related problem, use this simplified reasoning:

Confirm the exact failed function.
Check whether other functions still work.
Compare platform and ground controls when possible.
Confirm whether the electrical command reaches the output device.
If no command is present, remain on the electrical side.
If the command is present, check whether the motor, solenoid, or valve responds.
If the output device responds but movement still fails, continue into the hydraulic or mechanical system.
Confirm the failed component before ordering a replacement.

This sequence is simple, but it prevents many unnecessary part changes.

Common Diagnostic Mistakes

Calling Every No-Lift Problem a Hydraulic Problem

If the pump motor never receives a command, the hydraulic system may never have had a chance to operate.

Calling Every Intermittent Problem an Electrical Problem

Hydraulic valves, mechanical binding, and temperature-related hydraulic behavior can also create intermittent symptoms.

Replacing the Pump Because the Motor Runs

A running pump motor does not prove that the pump has failed. Valve position, hydraulic fluid supply, coupling, and downstream leakage also matter.

Replacing the PCB Because Several Functions Fail

Shared power or ground problems can disable several functions at once.

Ignoring Working Functions

Every function that still works helps eliminate components and systems from the diagnosis.

Frequently Asked Questions

How do I know if my scissor lift problem is electrical or hydraulic?

Start by determining whether the relevant motor, solenoid, or valve receives the correct electrical command. If the command never arrives, investigate the electrical side. If the command is present but the expected hydraulic response does not occur, move toward the hydraulic system.

If the hydraulic pump motor runs, does that mean the electrical system is good?

Not completely. It confirms that at least part of the electrical command and power path is working, but other electrical outputs and controls may still have problems.

If the pump motor does not run, is the hydraulic pump bad?

Not necessarily. Check power supply, control inputs, wiring, contactors, relays and the pump motor circuit before condemning the pump.

Can a bad valve look like an electrical problem?

Yes. If a solenoid receives the correct command but the valve spool sticks, the machine may appear to ignore the control input even though the electrical command is present.

Can low battery voltage look like a hydraulic failure?

Yes. Low electrical power can reduce pump-motor performance and make hydraulic functions appear weak or slow.

Should I replace the controller if several functions stop working?

Not before checking shared power, ground, communication, wiring, connectors and required safety inputs.

Related Scissor Lift Troubleshooting Guides

Final Thoughts

Electrical and hydraulic faults should not be treated as two completely separate worlds.

The electrical system creates the command. The hydraulic system creates the physical response. The most effective diagnosis follows that sequence and finds the point where the expected response stops.

If no command reaches the motor, solenoid, or valve, continue upstream through the controls and electrical system.

If the correct command reaches the output device but the machine still does not move correctly, continue downstream through the hydraulic and mechanical system.

That simple distinction can prevent unnecessary joystick, control-board, valve, motor, and pump replacement.

Diagnose the path first. Replace the part second.

Need Help Identifying the Correct Replacement Part?

SAIYIS supplies replacement electrical and hydraulic components for aerial work platforms, including control boxes, joysticks, control boards, hydraulic pumps, valves, motors, switches, and related scissor lift parts.

For compatibility verification, provide the original part number, complete machine model, serial number, and clear photos of the original component and its connectors.

If possible, also describe whether the electrical command reaches the component and what the machine does when that command is given.

Disclaimer: Manufacturer names and OEM part numbers are used for identification and compatibility reference purposes only. Electrical testing, hydraulic pressure testing, diagnosis, installation and repair should be performed by qualified personnel according to the appropriate equipment service documentation.