John Deere 744K Wheel Loader Low Brake Pressure Indicator Diagnostic

Symptoms

• Active 'Low Brake Pressure' warning indicator on primary dash display
• Brake pedal feels extremely soft or drops to floor plate with no resistance
• Parking brake fails to release when transmission direction is selected

Possible Causes

• Leaking or failed nitrogen-charged brake accumulator bladder
• Failing hydraulic brake charging pump or internal bypass control valve
• Damaged dual brake pedal control valve block seal system

Diagnostic Procedure

1. 1
   Conduct Accumulator Precharge Charging Pressure Check

   Test residual circuit pressure and check structural accumulator canisters. Discharge all pressure, connect nitrogen gas test tool, and measure pressure. Bladder must register within pre-charge specification (typically 800 - 1,000 psi).
2. 2
   Measure Brake Charging Valve Cut-in and Cut-out Pressures

   Attach 3,000 psi gauge to accumulator port on priority valve box. Run engine and read low/high trip pressures. Diagnostic cut-in should read 1,800 psi and cut-out should read 2,200 psi.
3. 3
   Inspect Pedal Control Valve for Internal Leakage

   Locate brake pedal control valve exhaust return ports. Measure leakage flow down block path when brake pedals are fully applied. Flow must be minimal; heavy bypass indicates worn spool seals.
4. 4
   Verify Brake Charge Sensor Functionality

   Test analog pressure sensor signals using the diagnostic menu. A standard sensor output signal ranges from 0.5 to 4.5 volts. Probe terminal pins to rule out harness wiring shorts.

Common Repairs

• Replace nitrogen charged brake system accumulator cannisters
• Reseal or rebuild the dual wheel brake valve block
• Replace pressure alarm warning sensor switch element

Safety Precautions

• Brake lines hold stored energy in nitrogen bladders even with engine off. Relieve all pressure.
• Wedge wood chock blocks against front/rear wheels before starting braking tests.

Required Tools

• Nitrogen gas accumulator testing tool kits
• High pressure manual pump depressurizing device
• 3,000 psi pressure measuring gauges

Related Fault Codes

People Also Ask

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• What does active code HYD 0112-01 mean on a John Deere wheel loader?
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Related Guides

Suggested Follow-Up Guides

• John Deere 744K Hydraulic Accumulator Charging and N2 Pressure Calibration Guide
• Troubleshooting and Replacing the John Deere 744K Brake Charging Valve
• How to Rebuild and Seal the John Deere Wheel Loader Park Brake Release Solenoid
• John Deere 744K Hydraulic System Flow Testing and Main Pump Diagnostics
• TCU Programming and Sensor Calibration Procedures for John Deere K-Series Loaders

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