Page 120
TROUBLESHOOTING
TEST DRIVE
Engine brake will not engage until coolant
temperature has reached 125°F (52°C).
1. Test drive the vehicle and measure intake
manifold boost pressure while operating the
engine brake (refer to table on page 120 for
boost pressures). It is best to conduct the
test with a loaded vehicle, engine at
maximum-rated RPM and the engine brake
ON. Downhill operation is desirable to
stabilize RPM.
RETARDING BOOST PRESSURES (PSI) WITH J-TECH™
ENGINE BRAKE
If the vehicle does not have a boost pressure
gauge, one must be installed. A pipe plug is
located in the air inlet manifold for this purpose.
2. Record the maximum boost pressure with
the engine brake switch in the HIGH
position.
3. Record the boost pressure with the engine
brake switch in the LOW position.
LOW position may be either front or rear unit.
4. Disconnect the wire lead from the LOW
position terminal of the engine brake switch
and rerun the test with the switch in the
HIGH position. Record the results.
The individual boost pressure readings should be
approximately the same as recorded in steps 3
and 4.
5. Compare the maximum boost pressure with
the specified boost pressures. A low reading
indicates a possible problem. Readings at
sea level should be within 3 psi of the values
shown (at higher altitudes, slightly lower
boost pressure readings are normal).
Readings within 3 psi of the values shown
indicate proper operation of the engine
brake.
With the J-Tech™ engine brake, a
significantly lower reading in one housing
indicates a possible problem with the
housing.
Electrical Troubleshooting
ASET™ engines have been equipped with a
V-MAC
®
control feature that automatically
provides a level of protection by activating the
engine brake only after the recommended
minimum oil temperature has been reached. Be
sure that the engine is sufficiently warmed before
conducting tests.
Some automated manual transmissions prevent
engine brake operation when the transmission is
in neutral.
NO ENGINE BRAKE OPERATION
1. Verify that the clutch pedal is not depressed
and that the clutch switch is working
properly.
2. Check for a blown fuse or circuit breaker.
3. With electrical power OFF, check the control
system for a short to ground. Check systems
separately to isolate where the short is
occurring. If the control system is OK up to
the engine brake valve cover/spacer
connection, measure the resistance to the
solenoid valve. High resistance means an
open circuit in the solenoid or solenoid wire.
Retarding boost pressures for MACK ASET™ engines
equipped with J-Tech™ engine brakes were not available
at time of publication.
5-111.bk Page 120 Monday, July 10, 2006 2:26 PM
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