Error code ca559

CA559 is a common rail fuel pressure low error, per the HeavyEquipmentFix fault-code database, matching entries across Komatsu's SAA6D107/SAA6D125-family engines (WA470-6 lists it as "supply pump pressure very low error," and the WA500-6 shares the same engine family). On a no-start, this means the ECM sees rail pressure well below commanded target during crank and is limiting or blocking fuel delivery rather than risking damage. The machine may experience issues such as the engine not starting at all or having difficulty starting, black exhaust gas, and reduced engine output.

Most likely causes, in order:

1. Supply (feed) pump not building low-pressure fuel to the high-pressure pump: check for air in the low-pressure circuit first, a loose fitting or degraded filter seal after a filter change is common. For checking pressure in the fuel low-pressure circuit, refer to "Testing and adjusting, Checking fuel pressure," measured at the fuel filter inlet side.
2. Fuel leak on the low or high pressure side: visually inspect for fuel leakage while running the engine at low idle if you can get it to fire even briefly; if it's a hard no-start, crank and watch the fuel filter housing and rail fittings for wetness.
3. Suction control valve (SCV) on the high-pressure pump sticking or out of spec. This is a known culprit on the same engine family: one field case on a related Komatsu excavator traced erratic rail pressure to the injection pump causing low rail pressure, with a suspicion that one of the plungers was bypassing fuel, and replacing the pump fixed it after an SCV swap didn't. Update, pump replaced, problem corrected.
4. Rail pressure sensor giving a false low reading, less common but cheap to rule out with a scan tool live reading.
5. Wiring/connector corrosion into the ECM or sensors, especially if the machine's been washed or sat in wet conditions.

First checks, cheapest first: verify no low-pressure air ingestion at filter housing seals, check fuel supply pump output pressure against spec at cranking/idle, then pull live rail pressure data on a scan tool while cranking to see if it's actually climbing or flatlined. Flatlined near zero points at the supply pump or SCV; climbing but capped low points at the sensor or a bypassing HP pump plunger. Confirming SCV resistance or swapping the HP pump is dealer-tool territory (Komatsu KDT) once you've ruled out the cheap stuff.

Post your engine model (SAA6D107/125) and whether it cranks with any injection attempt (smoke, noise) for a tighter call.