Rmc Module - Craftsman 28906 Professional Shop Manual

ELECTRICAL SYSTEM
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Symptom-After fire solenoid does not work:
enqine starts and dies: The after fire solenoid is
powered directly by the red wire from the B ter-
minal of the key switch, and should operate
independently of anything else on the tractor
once the engine is running. If the alternator fails
and battery power is not reaching the after fire
solenoid through the key switch, it will not work.
This is an unusual set of circumstances.
In the REVERSE CAUTION MODE (yellow
zone), the same characteristics are true as for
the normal run position, but in addition the L ter-
minal will have continuity with the A2 terminal.
The A2 terminal is connected to the RMC mod-
ule by a purple wire (electric PTO) or a white
wire (manual PTO). The L terminal (formerly
used for the lighting circuit) connects directly to
the ground circuit of green wires. When the key
is in the REVERSE CAUTION MODE position,
the purple wire carries a ground signal to the
RMC module. When the parking brake is not set,
this ground signal arms (enables), but does not
tum-on the RMC module.
Symptom-RMC module will not turn-on: Check
for continuity between A2 and L terminals on the
key switch when it is in the REVERSE CAUTION
MODE position. Confirm that the green wire has
continuity to ground. If the switch is capable of
establishing a ground signal to the RMC module,
the problem is likely to lie elsewhere in the sys-
tem.
Symptom-RMC module will not turn-on: confirm
that the ground path (continuity to ground) to the
purple or white wire is broken when the key
switch is in any position other than REVERSE
CAUTION MODE. The RMC module is disarmed
(disabled) when the parking brake is set. To re-
arm the module, the key is moved to another
position, breaking the ground signal, then
returned to the REVERSE CAUTION MODE, re-
establishing the ground signal. It works some-
thing like a latched relay. If it is not possible to
break the ground-path, it is not possible to
freshly establish it either, and the RMC module
will not be armable. Causes for such a condition
might include a shorted or incorrect key switch,
or a chafed purple wire shorting to ground
between the key switch and the RMC module.
RMC module
The RMC Module is in the same housing as the key
switch, and is not available separately. For the purpose
of diagnosis it is treated separately. Diagnosis of the
module with the key switch introduces too many over-
lapping variables. See Figure 7.3.
RMC Module
Key Switch
Figure 7.3
Principle: To diagnose the module, the simplest
approach is to check all of the inputs (safety cir-
cuits) that are connected to it. If the inputs work
properly, but the RMC module does not work
properly (outputs), then the module can be
determined to be faulty. A specific procedure is
covered, following the description of the correct
operation of the RMC module.
Working properly: The module cannot be diag-
nosed if it's function is not understood. It is
designed to work as follows: See Figure 7.4.
When the RMC module is disarmed, the tractor
will operate as MTD tractors have historical
operated:
If reverse is engaged when the electric PTO is
ON, the PTO clutch will turn-off. On tractors with
a manual PTO the engine will turn off.
If the operator leaves the seat with the engine
running, the engine will turn off.
If the operator leaves the seat with the PTO in
the OFF position, the engine will turn-off unless
the brake is applied.
When the RMC module is armed, the tractor will
operate identically to when the module is dis-
armed.
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