Applicable Systems
PC200 Excavator
Symptoms
The brake system pressure has dropped below the safe operating minimum. The parking brake engages automatically as a safety interlock, preventing machine movement.
Possible Causes
- Brake accumulator nitrogen charge low, reducing emergency brake reserve
- Brake master cylinder internal leak causing pressure bleed-down
- Brake line or fitting leak causing fluid loss
- Brake pressure sensor failure giving a false low reading
Troubleshooting Steps
- Step 1: Check the brake fluid level in the reservoir and inspect for external leaks
Top up with DOT 4 brake fluid and repair any visible leaks - Step 2: Measure the brake accumulator nitrogen precharge pressure
Should be 50% of the system relief pressure; recharge if low - Step 3: Connect a pressure gauge to the brake test port and verify the sensor reading
If gauge reads normal but the sensor reads low, replace the sensor - Step 4: Perform a brake pressure hold test: pressurize the system and monitor for 5 minutes
Pressure should not drop more than 10%; if it does, the master cylinder needs overhaul
How to Reset
Reset: Restore brake pressure above the minimum threshold. The parking brake releases automatically once pressure is confirmed.
Common Replacement Parts
- Brake accumulator: Nitrogen-charged, 1L capacity (Recharge to 80 bar nitrogen precharge)
- Brake master cylinder kit: Pistons, seals, and springs (Use only DOT 4 compatible materials)
- Brake pressure sensor: 0-250 bar, 4-20mA output (Match to machine electrical harness)
Frequently Asked Questions
- Q: How often should the brake accumulator be serviced?
Check nitrogen precharge annually. Recharge or replace if pressure drops below 80% of specification.
- Q: What brake fluid should I use?
DOT 4 heavy-duty brake fluid. Never mix DOT 3 and DOT 5 silicone fluids as they are incompatible.
Source: OEM Service Manual
Category: Heavy Equipment