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Volvo Engine Brake VE D12, D12A, D12B. Manual - part 5

Group 25

Troubleshooting

VEB Fault Symptoms

Fault symptom 1

The engine will not start

Probable fault:

•

The control valve plunger may be stuck in its rest
position. If this is the case, oil is fed to the rocker
arm shaft with full pressure and the plungers in the
rocker arm shafts will be pressed out. This will elimi-
nate the valve clearance and the decompression
lobes will open the exhaust valves. This impairs the
compression build-up and the engine cannot start.

Carry out mechanical troubleshooting.

Fault symptom 2

Neither the exhaust brake nor the compression
brake functions

This indicates a fault in the electrical system. The control
signal is not reaching the exhaust pressure governor and
the control valve solenoid valves.

Carry out electrical troubleshooting.

Fault symptom 3

The exhaust brake functions, but not the compres-
sion brake

Probable fault:

•

No control signal to the compression brake control
valve

•

Defective temperature sensor or diode

•

Defective control valve or control valve plunger stuck

•

No ground at coolant temperature switch

•

Drain channel is clogged

Carry out electrical troubleshooting.

If the fault remains:
Carry out mechanical troubleshooting.

Fault symptom 4

The compression brake functions, but not the ex-
haust brake

Probable fault:

•

No or low air pressure supplied to the EPG

•

No control signal to the exhaust pressure governor
solenoid valve

•

Defective solenoid valve

•

Defective exhaust pressure governor

•

Defective quick-release valve

•

Air leakage

Carry out electrical troubleshooting.

If the fault remains:
Carry out mechanical troubleshooting.

Fault symptom 5

Poor braking effect from the exhaust brake

Probable fault:

•

Low control pressure supplied to the EPG

•

Leaks in the exhaust manifold gaskets

•

Exhaust pressure governor seizing

•

Defective or leaking exhaust pressure governor

Carry out mechanical troubleshooting.

Fault symptom 6

Poor braking effect from the engine brake (exhaust
brake and compression brake)

Probable fault:

•

Low control pressure supplied to the EPG

•

The control valve gives too low oil pressure

•

Defective non-return valve in one or more of the
rocker arms

•

Defective pressure limiting valve in one or more of
the rocker arm plungers

•

The exhaust brake functions poorly or not at all

•

Exhaust valve clearance is too large

See the procedures in “Low Engine Braking Effect
(VEB)” page 21.

Fault symptom 7

The compression brake engages but will not disen-
gage

If the compression brake remains engaged with full ef-
fect even though the accelerator pedal is depressed, this
is due to the control valve plunger remaining in the”VEB
position”and directing full system oil pressure out to the
rocker arms.

Do not depress the clutch pedal unless necessary.
Engine may stop if compression brake stays engaged.
This will result in loss of power steering assistance.

If the compression brake only partly disengages, it is
most probable that one of the rocker arm plungers has
locked in its outer position. With this fault, the engine
runs unevenly due to low compression pressure in the
cylinder where the rocker arm plunger has stuck.

The fault generates one of the fault codes 31–36, as the
control unit compensates for the loss of power in the
cylinder by increasing the amount of fuel delivered to the
cylinder through the unit injector. When the maximum
amount of fuel delivered by the unit injector can not com-
pensate for the loss of power in the cylinder, the fault
code is generated.

Carry out mechanical troubleshooting.

Note: Fault codes 31–36 can also be generated by an
electrical fault in the fuel system.

Group 25

Troubleshooting

Low Engine Braking Effect (VEB)

Note: Before carrying out the following procedure, read
the troubleshooting general information in “Engine Brake,
Fault Tracing” page 15.

Check Before the Test:

•

That the conditions for exhaust braking and com-
pression braking are satisfied.

•

That the general condition of the engine is good.

•

That the engine has normal oil pressure.

•

That both the engine brake systems are functioning.

Check that both the exhaust brake and engine brake are
functioning by test-driving the truck.

•

Set the engine brake switch to OFF.

•

Drive the truck downhill, fully release the accelerator
pedal and set the switches to ON/LOW positions.
If the engine sound does not alter and/or there is no
braking effect, the exhaust brake does not function.
If the engine sound changes and there is a notice-
able braking effect, the exhaust brake does function.
Set the switches to ON/HI positions.

•

If no difference can be noted in the sound or in the
braking effect, the compression brake does not
function.

•

If the engine sound changes and there is a notice-
able braking effect, the compression brake does
function.

Check that the valve clearances are within the tolerance
range.

Test Equipment, Installation

1
Install the equipment for measuring the oil pressure in
the rocker arm shaft according to the instructions in “Oil
Pressure, Compression Brake, Checking” page 36.

2
Set the control switches to the OFF position (VEB dis-
abled). Start the engine and measure the rocker arm
shaft oil pressure. The pressure should be approximately
1 bar (14.5 psi).

If the pressure fluctuates or is under 0.5 bar (7.25 psi) or
over 1.5 bar (21.75 psi), the control valve is faulty.

Note: Low oil pressure in the rocker arm shaft may also
be due to excessive wear in the rocker arm bushings and
/or the rocker arms which result in excessive oil pressure
loss. See “Rocker Arm Roller, Checking” page 46.

3
Install the equipment for measuring the exhaust gas
temperature, including the 36-pin breakout box. See
“Exhaust Temperature, Checking” page 40.

Test-driving and Measuring

To obtain good test results, the exhaust pressure gover-
nor should be disabled when checking the function of
the compression brake.

•

Route the 36-pin breakout box into the cab and se-
cure.

•

Make sure the engine brake switch is OFF.

•

Bridge terminals 2 and 11 of the 36-pin breakout
box.

When terminals 2 and 11 of the 36-pin breakout box
are bridged, the compression brake will activate any-
time the VEB control switch is in the ON position,
regardless of status. The compression brake will re-
main ON until the control switch is moved to the OFF
position. While the engine brake is activated, do not
depress the accelerator or clutch. If the accelerator is
depressed, engine damage may result. If the clutch is
depressed a loss of power steering assist may occur.
Be prepared to switch off the engine brake at any time.
Failure to do so may result in personal injury or death.

When operating a vehicle on streets and highways,
during data collection procedure, it is mandatory to
have a second person drive while a technician col-
lects the data.

When engine braking, the exhaust gas temperature in-
creases on those cylinders where the compression brake
functions.

On the cylinder(s) where there is little or no braking ef-
fect there is very little exhaust gas temperature increase,
thus, the cylinder which gives a very low or no braking
effect can be identified.

Note: The temperature difference between cylinders is
not important when performing this test. Only note the
difference in temperature at the beginning and end of the
engine braking function on each individual cylinder.

For the measurement to be valid, select gears, speed
and section of road where the braking procedures can
be carried out continuously and without interruption.

Select a long, at least 1.2 mile (2 km), downhill section
of road, where the engine braking procedures can be
carried out without reducing the speed of the truck.

The truck should be loaded and the road conditions
clear.

Make sure that the engine brake switch(es) on the in-
strument panel are in the OFF position, until ready to
perform the test at the test location.

Group 25

Troubleshooting

Voltage supply to the measuring instrument is provided
by the cigarette lighter socket and the purpose of the in-
strument back-up mode is to prevent stored information
being lost if the external voltage supply is temporarily
broken.

When the external voltage supply is broken, the display
lighting goes out and the text begins to flash. If this oc-
curs during measuring, the stored values are retained
and the measurement procedure can continue when the
instrument voltage supply is restored.

The instrument can store 10 measurement values.
The first measurement value is stored as value A, the
second measurement value is stored as value B, the
third as value C etc.
The instrument can also calculate the difference between
two measurement values, for example B – A, D – C, etc.

Note: It is not possible to carry out measurements or
store measurement values when the instrument is in the
back-up mode.

Brake Test

T2008010

Check that the measurement instrument display shows
the text Temperature.

T2008011

Press

once.

The display should now show the text Temp. Display.

T2008019

Press

one more time.

The display should now show six temperature values,
one for each cylinder, with no. 1 cylinder shown on the
extreme left of the display.
The instrument will now measure temperature continu-
ously.

Accelerate the truck and select a gear that enables you
to hold a stable engine speed of approximately 1400
RPM when the accelerator pedal is completely released
(idle position).
(Use the service brakes as an aid in holding a stable en-
gine speed, as this procedure is to be performed with
the engine brake OFF.)

Group 25

Troubleshooting

T2008012

•

Completely release the accelerator pedal (idle posi-
tion).

•

While viewing the measurement instrument, wait for
the exhaust gas temperature to drop and begin to
stabilize.

•

Press

once.

The measurement value designation A is shown for
approximately 1 second on the display and is a confir-
mation that the value is registered and stored.

The measurement instrument then returns automatically
to continuous measurement and shows six measure-
ment values, one for each cylinder.

Set the engine brake switches to ON/HI. Read the rocker
arm shaft oil pressure on the pressure gauge when the
pressure has stabilized.
Note the value.

T2008013

•

View the measurement instrument, wait for the tem-
perature to rise and begin to stabilize.

•

Press

once.

The measurement value designation B is shown for
approximately 1 second on the display and is a confir-
mation that the value is registered and stored.

The measurement instrument then returns automatically
to continuous measurement.

Carry out the brake test and measurements at least
three times to obtain a valid result.

Note: Remember the engine brake will remain active un-
til switched OFF.

Store the measurement values by pressing

The instrument can store 10 measurement values (the
results from 5 measurements of Low / High tempera-
tures per cylinder).

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