1999 CAT 301.5 Hydraulic Pilot Pressure Issue – No Flow at Lockout Solenoid

Hi everyone, I’m working on a 1999 CAT 301.5 mini excavator (Open Canopy model) that has been sitting unused for about 3 years. I am trying to restore hydraulic pilot/joystick function. Here is what I have confirmed and tested so far: Pilot Pump Pressure: Tested at the pump port and confirmed a healthy 500 PSI. Electrical Interlock Circuit: 12V DC is reaching the hydraulic lockout solenoid under the floorboards when both safety console levers are lowered. The solenoid coil produces an audible click. Current Issue: Disconnected the inlet hose feeding into the lockout solenoid under the floorboards and idled the engine—there is virtually no oil reaching the inlet hose (just a slight dribble), so the restriction is definitely upstream of the floorboard solenoid block. Layout Notes: This machine has the two-block layout: the primary accumulator block is located in the rear, and the secondary solenoid block (housing the hydraulic lockout solenoid and 2-speed travel solenoid) is located under the floorboards. Questions for the forum:

1. Since there is no oil reaching the lockout solenoid inlet, is it almost certainly a seized check valve or a stuck pilot relief valve inside the rear accumulator block?
2. Has anyone found a way to access, remove, or flush the check valve or pilot relief valve in the rear block without having to completely tip or remove the cab/canopy structure?
3. Are there any clever tricks or inspection ports to flush that rear manifold block in place before I commit to pulling major body panels or the canopy off? Thanks in advance for any insights or experience you can share!

Would need a serial number to help us understand what you're looking at. There's two to choose from, and a couple of S/N breaks within them which have different arrangements.

Thank you serial number is 3YW00498

That’s the lockout solenoid where there’s no oil coming even getting to it on the inlet side.

That solenoid in your picture looks nothing like the hydraulic lockout solenoid shipped with your machine. Have anything that looks like this?... Do you have a hydraulic schematic?

First two diagrams are from the service manual and the other two are from the Cat parts lookup diagram

The illustration posted by @Chrisso is from the Parts Manual for your machine. It's more likely to be correct than a generic illustration. If you follow the wires from the solenoid in your photo back to the 2-pin connector from the machine harness, what are the wire colours on the machine side and can you see any numbers printed on the insulation on said wires.?

Found it... look up 143-2269 VALVE GP- SOLENOID -BOOM LOWERING. It allows a dead (but cranking) engine to fully pressurise the pilot accumulator after 15 - 20 seconds of cranking, which I just leaned now. So if you're not getting oil here at all, that leads us upstream to the pilot manifold and one of those two solenoids in the picture I posted earlier. It's either not getting current or there's no o-rings left inside valve section of the solenoid that screws into the manifold. Getting access to that valve does not look pretty, unfortunately. Got "Solenoid Valve (Work Tool Lowering) (RENR2805-03)" in your service manual?

Nige said: The illustration posted by @Chrisso is from the Parts Manual for your machine. It's more likely to be correct than a generic illustration. If you follow the wires from the solenoid in your photo back to the 2-pin connector from the machine harness, what are the wire colours on the machine side and can you see any numbers printed on the insulation on said wires.? Click to expand...

The boom lowering solenoid is located under the floor board on my machine. The issue is there’s no oil getting to it when the machine is on even when I disconnect the two hoses going into it. My logic is that the oil should be getting to it and when I lower the consoles the solenoid opens up and allows the oil to then come out the other hose and into the joysticks.

That’s from the manual

alex6708 said: The issue is there’s no oil getting to it when the machine is on even when I disconnect the two hoses going into it Click to expand... Yep… Chrisso said: So if you're not getting oil here at all, that leads us upstream to the pilot manifold and one of those two solenoids in the picture I posted earlier. It's either not getting current or there's no o-rings left inside valve section of the solenoid that screws into the manifold. Getting access to that valve does not look pretty, unfortunately. Click to expand...