The glow plugs first come ON when the engine
is below 120 OF (49 C) and the rotary switch
is turned to RUN. They stay ON for up to 9 seconds and
then go OFF. They will stay OFF for about 7-l 5 seconds
then come ON again for about 1 second, then go OFF
again. If you dont start the engine, the glow plugs should
keep cycling like this, due to the glow plug cycle timer in
the glow plugs controller.
If you start the engine, they will
cycle until the engine is warm, due to the afterglow cycle
timer in the glow plug controller.
When the engine gets up
to 120°F (49°C) the glow plugs should stop cyckng
If the glow plugs are cycling properly, you should hear a
click from the PCB when the glow plugs turn on and when
they turn off. This is the glow plug cycle timer, a thermal
A good way to check for cycling is
STE/ICE-R test 80, Battery Current. When the glow plugs
turn on, STE/lCE-R will measure 74-125 amps. When the
glow plugs turn off, the STEIICE-R will measure 3-8 amps.
ROTARY SWITCH IN RUN
If the glow plugs are cycling property, you can hear a click
from the PCB when the glow plugs turn on and when they
turn off (you may have to duck your head under the dash).
This is the afterglow cycle timer, a thermal circuit breaker.
A good way to check for cycling is STEIICE-R test 80,
When the glow plugs turn on, STEIlCE-R
will measure 74-125 amps. When the glow plugs turn off,
STE/ICE-R will measure 3-8 amps. As the engine gets
warmer, the glow plugs turn on less frequently and for
If you dont have a STEACE-R or a multimeter for measuring
current, you can watch the vehicle volts gauge for indication
of glow plug operation.
The glow plugs draw so much current
that the volts gauge should jump about half-an-inch to the left
when the glow plugs come on. Before starting the engine,
you should hear the glow plug power relay click open and
closed as the glow plugs cycle. (You can hear the relay after
the engine has started by leaning your head under the dash
near the PCB.) This method wont tell you if all the glow
plugs are working property, but it at least shows that the
glow plugs are trying to work and that the glow plug power
relay is working.
GLOW PLUGS CIRCUIT
EXPECTED GLOW PLUG CURRENT
ROTARY SWITCH IN RUN POSITION:
GLOW PLUGS ON: 74 - 125 AMPS 74 is only for
weak batteries. You should get at least 100 amps
when glow plugs are working property.
GLOW PLUGS OFF: AT or NEAR ZERO With the
rotary switch in the RUN position, other parts of
the vehicle are drawing current. You might
measure up to 8 amps.
STMCE-R TEST 80
1. Start Test 80. Battery Current.
2. Displayed reading is in amps. The reading will
be greater then 30 amps, depending on how
many accessories you have on.
1. Set the voltmeter to a DC volts scale of about 1
2. Connect the BLACK lead to the battery side of
the current shunt and the RED lead to the
other end of the current shunt.
3. Current shunt voltage is proportional to battery
current, 100 millivolts = 1 ,ooO amps. To get
current, multiply millivolts x 10.