GUEST POST BY BRIAN
KEYS, Former
Systems, Training & Resources Manager at the former Country Coach, LLC. ...Shared from several years back, written by an excellent technical writer I always enjoyed reading...Country Coach motorhome owners enjoy.
Won't Start?
Most starting problems
are caused by a tripped breaker, blown fuse, or sticking solenoid, and once the
fault has been identified, it can typically be corrected (if only temporarily)
within a matter of minutes.
Let’s begin by taking a
look at the various components of the system and how they are connected. The
circuit starts, of course, at the chassis battery itself, as shown on the
diagram below and from there chassis power goes directly to the starter motor
and to the chassis battery disconnect switch, followed by the chassis breaker
which in turn allows power to the chassis fuse panel, ignition solenoid, and
start solenoid.
When the key is turned
to the ignition position, the ignition switch receives power from the chassis
fuse panel on wire #50 and passes it onto the ignition solenoid on wire #34E.
This signals the ignition solenoid to close and pass power from the chassis
breaker through to the ignition fuse panel and also to the ECM (engine
computer) through an inline fuse (located at the solenoid on Allures or Intrigues
and in the electrical bay on Magnas, Affinitys and Lexas) and an ‘Engine Kill’
switch located in the engine compartment. With the key in the start position,
power is supplied from the ignition switch to the neutral start relay on wire
#33 and, assuming the transmission is in neutral, this power is forwarded to
the start solenoid on wire #33A which signals it to close. Once closed, the start
solenoid will pass power from the chassis breaker to the starter solenoid on
wire #33B through a breaker or fuse, depending upon the model of your coach.
Now that we know where
all the components are located and how they are connected,let’s take at look at
the four most common scenarios that you might experience should your coach fail
to start.
1. Nothing happens when you turn the
ignition switch to the ignition or start positions.
Make sure that the
chassis disconnect switch is turned on and reset the chassis breaker if it has
tripped. Check for loose or corroded chassis battery terminals or cable lugs
and use the battery boost if your chassis batteries are severely discharged. If
this does not solve your problem then check for power on the yellow wire #34E
at the ignition solenoid. If wire #34 has power then check the large terminals
on either side, if only one of these has power then the solenoid is sticking
and must be replaced. Gently tapping on the solenoid should allow it to close but
it may now stick in the closed position meaning that your engine will continue
to run when the key is turned off. Tapping on the solenoid again with the key
off should release it. This should only be considered as a ‘get you home’
measure.
If wire #34E does not
have power at the ignition solenoid then check the fuse for wire #50 in the
chassis fuse panel and make sure that the wiring at the ignition switch is
intact.
2. Dash and other ignition systems
power up when the key is turned to the ignition position but nothing happens
when the key is turned to the start position.
With the ignition on,
verify that the transmission is in neutral, and then check for a tripped
starter breaker or blown starter fuse. Check for power on blue wire #33A at the
start solenoid behind the rear bumper on the passenger side. If wire #33A has
power, then check the large terminals on either side of the solenoid. If only
one of these terminals has power, then the solenoid is sticking and must be replaced.
Gently tapping on the solenoid should allow it to close but it may now stick in
the closed position meaning that your engine will continue to crank when the
key is turned off. Tapping on the solenoid again should release it but as before,
this should only be considered as a ‘get you home’ measure.
If you hear a loud clunk
when the key is turned to the start position and both sides of the start
solenoid have power, then the gear on the starter motor is probably unable to ‘mesh’
with the gear on the engine flywheel. Although extremely rare, this can and
does happen, with the only cure being to manually turn the engine a little
using a large socket and bar on the crankshaft pulley or to momentarily spin
the starter motor by bypassing the starter solenoid on the motor itself. The
latter should only be done by a professional mechanic.
3. Dash and other ignition systems
power up when the key is turned to the ignition position and the engine cranks
but will not start.
Assuming you have not
run out of diesel, then the first thing to check would be the engine kill
switch on the right side of the engine compartment. If the engine kill switch
has not been activated, then check the inline fuse that provides ignition power
to the ECM or Electronic Control Module. This fuse is located at the ignition
solenoid on Allures or Intrigues and in the electrical bay on Magnas, Affinitys
and Lexas. If the ‘Check Engine’ light on your dash is illuminated or flashing,
then there is most likely an engine fault that you will need to have investigated
by a Cummins or Caterpillar dealer. Earlier coach models used an engine kill
relay located on the right of the engine compartment next to the engine kill
switch and this relay can prevent your engine from starting, especially if the
engine kill switch has been used recently. The relay is available at most local
parts stores and can be changed in a matter of minutes.
4. Engine starts but will not continue
running when the ignition key is released.
This situation is
unheard of on current models with ECM’s or Engine Computer Modules. If you have
an earlier model coach, however, with a non-electronic engine, this condition
could indicate that the coach’s Engine Protection Module is preventing the
engine from running. This is generally caused by a critical condition such as
low oil pressure, hot coolant, or low coolant level triggering that device.
These coaches have been provided with a foot-actuated override switch located
near the driver’s right foot. Depressing this foot switch will allow you to
start and drive the coach long enough to pull safely off the road. In these
cases, it is prudent to check the obvious things first, such as coolant and
engine oil levels. If the problem is caused by a temporary overheat situation,
you may be able to wait until the engine cools down sufficiently to re-start
and then continue on your way. In the case of low coolant level (one of the
most common culprits), replenishing the coolant level and cycling the ignition
key off and back on should allow the coach to start and run normally. In addition
to these situations, a failed fuel solenoid can cause this no-run symptom, but
this is an item that will require the skills of a professional mechanic.
Hopefully, you’ll never
have to encounter a disabling scenario like those discussed above, but having a
bit of knowledge about your coach’s chassis electrical system may save you some
grief and expense.