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Troubleshooting
793F and 797F Off-Highway Trucks Braking System
Media Number -KENR8395-09 Publication Date -01/11/2014 Date Updated -11/07/2017

i07081715

E527 High Brake Pump Command

SMCS - 4014-035

Illustration 1 g02433236

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Tools to help diagnose issue: Cat® ET data log,

Illustration 2 g02433262
A Cat® ET data log file
(E) Poor charge time
(15) Poor stability

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Illustration 3 g02433264
A Cat® ET data log file
(F) Good charge time
(16) Good stability

Refer to Systems Operations, KENR8738, "Control Valve (Brake)" for the locations of the
components in the table below.

Table 1
Problem: EID 527 High Brake Pump Command is active if the engine is running, and the
brake system is charging for more than 90 seconds without cutting out.
Possible Non-
Corrective
Component Component Component How to Diagnose
Action
Root Causes Root Causes
Solenoid Contamination: Open circuit/short to ground
Replace
Valve (Brake Seal Brake system fault codes logged in ET.
Solenoid
Pump Damaged oil Measure coil resistance when
Valve (Brake
Unloader) causing (significantly) cool 20° C (68° F). The
Pump
leaking. dirtier than ISO resistance should be close to 32
Unloader).
18/15 +/- 2 ohms.
Valve Harness Stuck Closed: Measure actual Make sure that
improperly connector not brake pump pressure. Install oil is ISO
installed locked in place 35000 kPa (5000 psi) gauge on 18/15 or
causing brake pump pressure tap. Brake better. If more
pump pressure at than 18/15,

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screen 22408 ± 345 kPa

damage (3250 ± 50 psi) relief pressure
constantly.
Remove the access plug for
kidney loop
OR1. Install a 35000 kPa
machine and
(5000 psi) gauge. Pressure at
change filter.
OR1 is the same as pump
If kidney loop
discharge pressure, replace
not available,
solenoid valve.
change oil.
Bent or
damaged Remove solenoid and visually
solenoid inspect screen for damage.
valve.
Pumping over relief valve for an extended period > 90 seconds
Stuck Closed: Measure actual
brake pump pressure. Install
35000 kPa (5000 psi) gauge on
Replace Valve
brake pump pressure tap. Brake
(Brake Pump
pump pressure at
Unloader).
22408 ± 345 kPa
Stuck Open (3250 ± 50 psi) relief pressure
or Closed constantly.

Contamination: Remove the access plug for

Brake system OR1. Install a 35000 kPa
Valve(Brake (5000 psi) gauge. Pressure at Make sure that
oil
Pump OR1 is less than brake pump oil is ISO
(significantly)
Unloader) pressure, replace Valve. 18/15 or
dirtier than ISO
18/15 better. If more
Stuck Open: Measure actual
than 18/15,
brake pump pressure. Install
kidney loop
35000 kPa (5000 psi) gauge on
machine and
brake pump pressure tap. Brake
change filter.
Seal damage pump pressure at standby
If kidney loop
constantly.
not available,
Remove valve and visually change oil.
inspect to determine if valve
stuck open
Relief Valve Stuck Open Contamination: Stuck Open: Measure actual Increase
(Main) Brake system brake pump pressure. Install Relief Valve
oil 35000 kPa (5000 psi) gauge on (Main)
(significantly) brake pump pressure tap. Brake pressure
dirtier than ISO pump pressure at low pressure setting.
18/15 constantly.
Replace Relief
Valve (Main).

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Make sure that

Drifting Low: Measure actual oil is ISO
brake pump pressure. Install 18/15 or
Pressure 35000 kPa (5000 psi) gauge on better. If more
Setting brake pump pressure tap. Brake than 18/15,
Drifting Low pump pressure below Brake kidney loop
causing a Accumulator cut out pressure machine and
stalled charge ( 20684 kPa (3000 psi)). Low change filter.
Idle Charging may stall or If kidney loop
charge time be extended. not available,
change oil.
If you cannot reach cutout at
low idle, the pump efficiency is
possibly too low. To test, run
Tank line into bucket and plug
Tank port on tank. Disconnect
charging solenoid and
accumulator purge solenoid.
Activate engine kill switch
(Engine will not start) and
Transmission lockout switch-on
bumper. Turn over engine until
air tank drains two times. If
little oil drains out of tank line
replace pump due to no large
leakage in rest of system. If oil
does discharge out of the tank
Contamination:
port, measure and track the
Brake system
Poor accumulator pressures. If
oil Replace Brake
Brake Pump Volumetric pressure at service accumulators
(significantly) Pump.
Efficiency drops quickly, inspect the
dirtier than ISO
service brake valves. If the
18/15
secondary accumulator
pressures drop quickly, inspect
the secondary brake valves. If
accumulators do not drop
quickly, inspect the system
relief valve. After testing, insure
that the charging solenoid and
accumulator purge solenoid are
reconnected. Reconnect all lines
and dry crank engine again,
allow accumulators to purge
back to tank. After
accumulators have been purged,
work may begin on the truck.
After the procedure is complete,
the brakes must be purged.

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Harness With machine off, verify that

connector not the sensors are reading less than
locked in place 517 kPa (75 psi).

Brake Failed In Install 35000 kPa (5000 psi) Replace Brake

Accumulator Range /Stuck gauge on the brake accumulator Accumulator
Pressure at one Locking tab pressure taps to verify that the Pressure
Sensors pressure broken on accumulator pressure matches Sensors.
mating the gauge pressure. With
connector. machine running at low idle
check to see if the gauge
matches the sensor in Cat® ET.
Replace
Solenoid
Short to Valve Gp
Short To Battery Fault Code
Battery (Brake
Accumulator
Purge)
Contamination:
Solenoid Make sure that
Brake system
Valve Gp oil is ISO
oil
(Brake 18/15 or
(significantly)
Accumulator better. If more
dirtier than ISO If you cannot reach cutout at
Purge) than 18/15,
18/15 low idle and both accumulators
Stuck Open kidney loop
cycle rapidly, then the valve
machine and
could be stuck open.
change filter.
If kidney loop
not available,
change oil.
Contamination:
Incorrectly Brake system
Check Valve Verify arrow on hex of check Properly
installed in oil
(Hoist Pilot valve is flowing in the correct install check
place of tow (significantly)
Check) direction. valve.
motor check. dirtier than ISO
18/15
Contamination:
Incorrectly Brake system
Check Valve Verify arrow on hex of check Properly
installed in oil
(Tow Motor valve is flowing in the correct install check
place of hoist (significantly)
Check) direction. valve.
pilot check. dirtier than ISO
18/15
Filter Damaged on System Remove filter element and Contact
Element Installation Overheating inspect for damage and loose product
pieces of yellow plastic. support
Remove and inspect through the
DSN.

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Accumulator purge solenoid

screens for debris.

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All Rights Reserved.
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