1. Fault Symptoms

On-site, the operator reported that the boom sometimes moves fast and sometimes slow, showing random behavior. The issue is intermittent: sometimes the machine works a whole day without problem, while at other times it occurs four to five times within an hour. This fault affects normal excavator operation.

2. Fault Inspection

• This is an intermittent fault, requiring step-by-step investigation.

• Using a multimeter to check the sensor’s 5V signal revealed unstable voltage.

• Unstable voltage indicates a possible short circuit or poor contact in the wiring.

• In Hitachi excavators, hydraulic oil leaks often cause wiring aging and wear.

• Inspection of the metal clips securing the wiring identified the damaged point as the fault source.

• After repairing the wiring, testing confirmed the boom movement returned to normal.

3. Fault Summary

• Wiring aging and wear due to oil leakage is a common issue in Hitachi excavators.

• Checking the metal clips that fix the wiring is key to troubleshooting such intermittent faults.

• Regular inspection of wiring clips and protective measures is recommended to prevent recurrence.

Hitachi 470 Boom Slow Speed – Troubleshooting Flowchart

Step 1: Observe and Confirm Fault

Symptom: Boom speed sometimes fast, sometimes slow (intermittent).

Note frequency: occasional (few times/hour) or rare (once/day).

Ensure operator logs time and conditions when fault occurs.

Step 6: Preventive Measures

Step 5: System Test

Step 4: Trace Wiring

Step 3: Sensor Voltage Test

Step 2: Preliminary Checks

• Regularly inspect wiring harness and metal clips, especially near oil-prone areas.

• Apply protective sleeves or reposition clips to avoid future rubbing.

• Log any recurring faults for further ECM or sensor inspection.

• Restart machine and operate boom under various speeds.

• Confirm that boom moves smoothly and consistently.

• If still intermittent → re-check sensors and connectors.

• Repair or replace damaged sections of wiring or clips.

• Inspect metal clips fixing the harness along the boom and chassis.

• Look for abrasion, short circuits, or contact failure, often caused by oil exposure.

• Use a multimeter to check the boom sensor 5V reference signal.

• If voltage is unstable → wiring issue suspected.

• Check for visible hydraulic oil leaks around boom cylinders and lines.

• Inspect boom cables, harnesses, and connectors for wear or damage.