PLATE 7I2721 - Caterpillar

Illustration 1 g02433406
Tools to help diagnose issue: Cat® ET data log, VIMS snapshot, and others.
Table 1
Problem: EID 653 Low Secondary Brake Accumulator Pressure is active if the engine has been running for 10 seconds, the truck has been in gear for 2.5 seconds, and Accumulator pressure is less than 12300 kPa (1784 psi) for more than 2.5 seconds. Level 3 is machine is moving and Secondary Brake Accumulator Pressure is less than 6900 kPa (1000 psi) for 2.5 seconds.
Component Possible Component Root Causes Non-Component Root Causes How to Diagnose Corrective Action
Brake Accumulator Pressure Sensors With machine off, verify that the sensors are reading less than 517 kPa (75 psi).
Failed In Range /Stuck at one pressure Install 35000 kPa (5000 psi) gauge on the brake accumulator pressure taps to verify that the accumulator pressure matches the gauge pressure. With machine running at low idle check to see if the gauge matches the sensor in Cat® ET. Replace Brake Accumulator Pressure Sensors.
Accumulator Low Pre-charge Leaking Accumulator Gas Valve Follow Accumulator Gas Charging Procedure Recharge Accumulator to specifications
Oil Trapped in the Gas side of the accumulator Failed piston seals Connect hose to charge valve. Drain into a suitable container. Start the truck and let the accumulator piston push the oil into the container. There should not be more than a cup of oil. Replace or rebuild the accumulator if too much oil is leaking past the piston seals.
Solenoid Valve (Brake Pump Unloader) Seal Damaged causing leaking. Contamination: Brake system oil dirtier than ISO 18/1 Connect Cat® ET and compare the time from Unloader Status changes to how fast the brake pump pressure rises. If the pressure rises too slowly, the valve could have an internal failure. If system can reach cut-out pressure, insure time between charges for service brake is greater than 25 seconds and for secondary is greater than 60 seconds. If either fails, review the frequent service brake charging or frequent secondary brake charging table. Replace Solenoid Valve (Brake Pump Unloader).
Valve improperly installed causing screen damage Make sure that oil is ISO 18/15 or better. If more than 18/15, kidney loop machine and change filter. If kidney loop not available, change oil.
Slow to Close Stuck Open: Measure actual brake pump pressure. Install 35000 kPa (5000 psi) gauge on brake pump pressure tap. Brake pump pressure at standby constantly.
Partially stuck open Remove the access plug