Start at the pilot circuit, because a dead machine with a live engine almost never has a failed main pump. Confirm the safety lock lever and its switch are actually enabling the pilot lockout solenoid, then measure pilot pressure at the pilot manifold with the engine at rated speed and the oil warm. If that reading is not at the specification in the service manual, the fault sits upstream of every control valve on the machine and no amount of work on the main pump will change it. If pilot pressure is correct, prove that the pump regulator receives its signal and that the regulator spool is free to move. Only when pilot supply and pump control are both proven does the main relief, and then the pump itself, deserve attention. A machine where some functions work and others do not is a different fault and is not covered by this sequence.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Every function dead, engine starts and idles normally | Pilot supply or pilot lockout. The engine side is fine, which is why the fault feels electrical and is usually hydraulic. |
| Functions work only while the safety lever is held by hand | The lockout switch is not latching in the released position. A switch or its adjustment, not a pump. |
| Machine creeps very slowly with no power at all | Pilot pressure is present but low. Enough to crack the spools open, nowhere near enough to stroke the pump. |
| Engine note does not change when a function is commanded | The pump is not being asked to do work. Either no pilot signal reaches the regulator or the regulator is stuck at minimum displacement. |
| Solenoid clicks when the lever is moved but nothing happens | The electrical command arrives and the hydraulic result does not. Look at the valve the solenoid shifts and at the pilot oil behind it. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Pilot lockout solenoid unpowered or failed | The most common single cause of a completely dead machine. Confirm supply voltage at the solenoid with the lever down, then confirm the solenoid actually shifts its valve rather than merely clicking. |
| Safety lever switch out of adjustment or contaminated | A switch that never makes tells the controller the lever is up permanently. Look at the switch state in the monitor before touching anything hydraulic. |
| Pilot filter collapsed or pilot pump worn | Pilot flow is small and unforgiving. A restricted pilot filter drops pressure across itself, and a worn pilot pump delivers volume at low pressure, which reads as a weak machine everywhere. |
| Pump regulator spool stuck, or its pilot line blocked | The regulator needs a clean, pressure-true signal. Contaminated oil or a crushed pilot hose leaves the pump at minimum displacement with correct pilot pressure at the manifold. |
| Main relief stuck open or unloading valve held open | Oil goes over relief from the moment the pump strokes. Rare compared with pilot faults, which is why it belongs last in the sequence, not first. |
The sequence, and what each result eliminates
| Check | What it tells you |
|---|---|
| Safety lever switch state in the monitor | Whether the machine knows the lever is down. If not, nothing downstream can work. |
| Voltage and ground at the lockout solenoid | Whether the command reaches the valve. Clicking is not proof of shifting. |
| Pilot pressure at the manifold, hot, rated speed | The single most informative reading on a dead machine. |
| Pilot pressure at the pump regulator inlet | Whether the signal survives the route. A drop here isolates a line or fitting. |
| Regulator spool travel when a function is commanded | Whether the pump is being asked to stroke. If it is, the fault is downstream of the pump. |
How to confirm it
- Confirm the lever, the switch and the solenoid before opening anything
With the engine off, watch the lockout switch state in the monitor as the lever is lowered, then measure voltage at the solenoid with the key on and the lever down. This ten-minute check resolves a large share of dead machines and costs nothing but time.
- Measure pilot pressure at the manifold, oil hot
Tee a gauge into the pilot manifold, run the engine at rated speed, and read with the oil at working temperature. Cold oil flatters a worn pilot pump, and a cold reading is how a weak machine gets sent out again.
- If pilot pressure is low, split supply from demand
Cap the pilot circuit downstream of the gauge and read again. Pressure recovering means a leaking or stuck consumer; pressure staying low means the pilot pump, its relief or the filter is the limit.
- If pilot pressure is correct, follow the signal to the regulator
Measure at the regulator inlet rather than assuming the manifold reading arrives intact, then watch spool travel while a function is commanded. This is where a blocked pilot line or a stuck spool reveals itself.
- Prove the pump and relief only after the circuit is proven
If the regulator strokes and the machine still does not move, confirm main relief setting and pump delivery against specification. Guangzhou Shenyue Machinery Technology Co., Ltd. supplies pilot pumps, lockout solenoids, regulator parts and pilot filters for common excavator models, quoted from the machine serial number rather than the model alone. Stock is held as 3,000+ part types on the shelf, with 100,000+ part numbers available to order.
What to do about it
Restore the lockout command Adjust or replace the lever switch, repair the solenoid circuit, and verify the valve shifts by pressure rather than by sound. This is the repair in most no-function cases, and it is also the cheapest.
Restore pilot pressure to specification Replace the pilot filter, repair the pilot relief if it is weeping, and replace a worn pilot pump. Anything less leaves every function on the machine slightly wrong instead of completely dead, which is harder to diagnose later.
Free or replace the pump regulator Clean the spool and bore, replace damaged seals and any blocked pilot hose. Record the regulator setting before disassembly, because adjustment is not part of a cleaning job.
Correct main relief if it is passing Reseat or replace the valve and set it to specification on a gauge, hot. A relief left at the wrong setting turns a correct repair into a machine that still feels weak.
Find what contaminated the circuit A stuck spool and a blocked pilot filter both have an upstream cause. Without that step the same fault returns in a few hundred hours with a fresh set of parts in it.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Pilot pump | Genuine; OEM-quality. Supplied against machine serial number and pump code. |
| Pilot lockout solenoid and valve | Genuine; OEM-quality. Coil voltage and connector type confirmed before dispatch. |
| Pilot filter element | Genuine; OEM-quality; aftermarket. Rating stated on every quotation. |
| Pump regulator parts and seals | Genuine; OEM-quality. Matched to the regulator series, not to the machine model alone. |
| Main relief valve assembly | Genuine; OEM-quality. Setting verified before dispatch where the valve is adjustable. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
Why does the machine have no functions at all rather than weak ones?
Because the pilot circuit is a supply, not a share. When it fails, every valve on the machine loses its command at the same moment, so the symptom is total rather than proportional. Weak but working functions point at pilot pressure that is low, or at a pump that is not stroking fully, which is a different repair.
Can a failed main pump cause a completely dead machine?
It can, but it is far less common than a pilot fault and it is not the first thing to prove. A pump that has failed internally usually leaves some function with pressure and often makes noise or heats the oil. Prove pilot supply and regulator response first; a pump replaced on suspicion is the most expensive guess in this trade.
The solenoid clicks, so is the electrical side fine?
No. A solenoid can click without shifting its valve, and it can shift its valve without pilot oil arriving behind it. Measure pressure downstream of the valve with the lever down. Sound is not a measurement, and treating it as one is how a good solenoid gets replaced twice.