One jack that won't extend, a system that levels halfway then stops, hydraulics that drift overnight, or a controller throwing an error with no clear cause — this guide covers how to find what's actually wrong and what to do about it.
The leveling systems lesson covered how electric and hydraulic systems work, why the known starting point matters, and what error codes mean at a high level. This guide is where you take that knowledge into actual diagnosis — testing under load, isolating a single jack, working through hydraulic symptoms, and understanding when the controller is the problem versus when it's just reporting one.
Start with 12V power before diagnosing the leveling system.
The majority of leveling system failures traced back in the shop are battery or connection problems — not controller or jack failures. A leveling system under load draws 20–40 amps. Weak battery voltage collapses under that load and the controller faults out. Check battery voltage under leveling load before going further.
Specific test procedures, the exact readings you should see, and what it means when something's off. The kind of detail that tells you whether this is a $12 fix or a call to your dealer.
And you won't be working through it alone. A diagnostic chatbot built on 21 years of real field experience is coming soon — so when you hit a wall, you can ask the question directly.
This is always the first test. A controller that reads battery voltage at idle will show a completely different picture when the jack motors are running. If voltage collapses under load, the controller will fault, jack movement will be slow or erratic, and the system will behave as if it has a component failure when the real problem is power delivery.
After confirming battery voltage is adequate, measure at the controller's power input terminals during operation. The difference between battery voltage and controller input voltage is the drop across the supply wiring and connections. More than 0.5V of drop indicates resistance in the supply path — undersized cable, corroded connections, or a failing fuse/breaker. Find and correct the drop before condemning the controller.
Electric leveling systems use either 12V DC motors driving screw actuators (scissor jacks, through-frame jacks) or motor-driven gear assemblies (slide-out style landing gear on fifth wheels). Each jack has its own motor, and the controller commands them individually or in pairs.
When a single jack fails while others work, the problem is almost always local to that jack — not the controller. Start at the jack motor connector. With the system commanding that jack to extend, measure voltage at the motor connector. Should read battery voltage (12V+) on the positive terminal relative to chassis ground.
| Voltage at Motor Connector | What It Means | Next Step |
|---|---|---|
| 12V+ present, motor doesn't run | Motor has failed or is mechanically seized | Test motor resistance; inspect for physical binding |
| 0V — no voltage reaching connector | Wiring, relay, or controller output fault | Trace back toward controller; test relay |
| Voltage present but low (under 10V) | Voltage drop in the supply wire or ground | Check wire gauge, connectors, ground point at jack |
With the motor connector disconnected and power off, measure resistance across the motor terminals with an ohmmeter. A functional 12V DC motor typically reads 0.5–3 ohms depending on winding design. An open circuit (OL) reading indicates a broken winding — motor needs replacement. A reading near zero ohms indicates a shorted winding — also replacement. A reading in the expected range means the motor is electrically intact; the problem is mechanical binding or a controller output issue.
Jack motor connectors are exposed to road debris, moisture, and movement — they're a common failure point. Inspect for corrosion, pushed-back pins, and damaged insulation at the connector body. Wiggling the connector while commanding the jack should not change behavior — if it does, the connector is the problem. Clean with electrical contact cleaner, inspect pin retention, and apply dielectric grease on reassembly.
Each jack motor needs a clean ground path. Most use the jack body itself as the ground return, which means the ground continuity runs through the mounting bolts to the chassis. A loose mounting bolt or corroded mounting surface creates a high-resistance ground that causes the motor to run slowly or not at all despite correct voltage at the positive terminal. Measure resistance from the motor housing to chassis ground — should read under 0.5 ohms.
Hydraulic systems use a central pump and manifold to deliver fluid pressure to individual cylinders. The pump motor runs 12V DC; the manifold contains solenoid valves that direct fluid to each cylinder. Failures occur in the pump, the solenoids, the cylinders, or the fluid itself.
A system that levels correctly but slowly drops over hours or overnight has a fluid leak — either internal (past a cylinder seal) or external (at a fitting or hose). Internal cylinder seal leaks are the most common: fluid bypasses the piston seal and the cylinder retracts under load. To confirm internal vs external: wipe all external fittings and hoses dry, then re-level and wait. External leaks will show fluid. Internal leaks leave no external trace — the cylinder just slowly loses position.
A leaking solenoid valve in the manifold can also allow fluid to return to the reservoir when it should hold. To test: with the system leveled and hold engaged, close the manual shutoff valve between the pump and manifold (if equipped). If drift stops, the leak is in the manifold or a solenoid. If drift continues, the leak is in a cylinder or line downstream of the shutoff.
If the pump motor runs but jacks move slowly or not at all, the pump may have low output pressure. Connect a hydraulic pressure gauge to the test port on the manifold (most HWH and Lippert systems have one). With the pump running and a jack commanded to extend against a stopped load, system pressure should reach 2,000–2,500 PSI depending on the system spec. Low pressure with a running pump indicates pump wear, low fluid level, or a stuck pressure relief valve. Check fluid level first — a pump running low on fluid will cavitate and produce low pressure without any other symptoms.
Hydraulic fluid that appears milky, foamy, or dark brown has been contaminated — usually with water from a failed reservoir seal or a ruptured line fitting. Contaminated fluid destroys pump seals and solenoid valve seats. A full fluid flush and system bleed is required. Do not simply top off contaminated fluid — diluting bad fluid with good fluid doesn't fix the problem.
When the controller displays an error and you've confirmed power is adequate and individual components test correctly, the question is whether the controller itself has failed or is accurately reporting a fault elsewhere. Controller bypass testing answers this without needing a replacement controller on hand.
Most Lippert and HWH electric systems allow direct operation of individual jacks by applying 12V directly to the motor connector — bypassing the controller entirely. With the controller disconnected from a jack's motor leads, apply 12V positive to the motor's extend terminal and ground to the motor ground. If the jack operates normally with direct power, the motor is functional and the problem is the controller's output to that jack — either a failed output driver or a wiring issue between controller and motor.
If the jack still doesn't operate with direct power applied, the problem is in the motor, the ground path, or a mechanical binding — not the controller.
Bypassing the controller removes all safety interlocks — the system will not prevent you from extending jacks while in travel mode or running jacks past their limits. Use bypass testing only for diagnosis with the RV stationary, and only long enough to confirm or rule out a component. Do not use bypass mode as a workaround for normal operation.
When the controller has failed completely and the system won't respond, manual override allows you to retract jacks for travel. The procedure varies by manufacturer — using the wrong method on the wrong system can damage components.
Lippert electric systems have a manual override button on the controller that holds for 3 seconds to enter manual mode. In manual mode, individual jack buttons operate the jacks directly. If the controller is completely dead, each motor can be operated by applying 12V directly to the motor connector as described above — use a fused jumper wire (20A fuse minimum).
HWH hydraulic systems have manual dump valves on the manifold — small brass screws or hex fittings that, when loosened, allow fluid to return to the reservoir and the cylinder to retract under the weight of the coach. Loosen gradually — the jack will retract. Do not remove the fitting completely. Once retracted, re-tighten before travel. Location of dump valves varies by coach — consult the HWH component tag on the manifold for the system ID, then download the corresponding manual from HWH's website.
Equalizer electric systems include a manual switch panel or a hand pendant as standard equipment — this is the override. If the main controller is non-functional, the pendant or manual panel operates each jack independently on direct 12V. If neither the pendant nor the panel works, apply 12V directly to the individual motor connectors as described under controller bypass.