Check Power Supply To Wire 56; Check Starter Contactor - Guardian 4700 Repair Manual

Section 7
DIAGNOSTIC TESTS
2. If engine cranks in Step 3 when Wire 17 is grounded, but will
not crank when the Switch is set to "START", replace the Start-
Stop switch.
3. If the Start-Stop Switch (SW1) failed any part of Steps 5 or 6,
replace the switch.
4. If engine will not crank when Wire 17 is grounded, proceed as
follows:
a. Use a jumper wire to connect the circuit board's
Wire 17 (pin location J1-6) to ground. If engine
does NOT crank, proceed to Test 25.
b. If engine cranks now, but would not crank in
Step 3 of the procedure, check Wire 17 for con-
tinuity between the circuit board and Start-Stop
Switch. If continuity is not measured, repair or
replace Wire No. 17 between the engine control
board and the Start-Stop switch.
TEST 25 - CHECK POWER SUPPLY TO WIRE 56
DISCUSSION:
If battery voltage is available to the Engine Controller
board in Test 23, then DC voltage should be deliv-
ered to Wire 56 when the Start Switch is set to
"START" (Test 24). This test will check to see if the
circuit board is delivering battery voltage to the Wire
56 terminal.
PROCEDURE:
1. Set a VOM to measure DC voltage (12 VDC).
2. Disconnect Wire 56 from its Starter Contactor terminal.
3. Connect the meter positive (+) test lead to Wire 56, just discon-
nected. Connect the other test lead to frame ground. No volt-
age should be indicated.
4. Actuate the Start-Stop Switch to its "START" position. The
meter should indicate battery voltage. If battery voltage is pre-
sent, stop the procedure.
5. Connect the VOM positive (+) test lead to Wire No. 56 (Pin
Location J1-1) at the Engine Controller Circuit Board. Connect
the other test lead to frame ground.
6. Actuate the Start-Stop Switch to the "START" position. The
meter should indicate battery voltage.
RESULTS:
1. If battery voltage was measured in Step 6, but not in Step 4,
repair or replace Wire No. 56 between the Engine Controller
Circuit Board and Starter Contactor.
2. If battery voltage was not available in Step 6, replace the
Engine Controller Circuit Board.
3. If battery voltage is available in Step 4 but engine does not
crank, go to Test 26.
Page 42
TEST 26- CHECK STARTER CONTACTOR
DISCUSSION:
If battery voltage is available to the Wire 56 circuit,
but engine won't crank, one possible cause of the
problem is a failed Starter Contactor.
PROCEDURE:
1. Set the VOM to measure resistance ("R x 1" scale). Connect
one test lead to Wire No. 0 on the Starter Contactor terminal.
Connect the other test lead to frame ground. Continuity should
be measured.
2. Momentarily connect a suitable jumper cable across the two
large terminal studs of the Starter Contactor. The engine
should crank.
Short to Ground:
3. Set the VOM to measure resistance. Disconnect Wire No. 56
from the Starter Contact terminal. Connect one meter test lead
to the Starter Contact terminal from which Wire No. 56 was just
removed. Connect the other meter test lead to a clean frame
ground. A Starter Contactor coil resistance of 3.9 ohms should
be measured. If continuity is measured, a short to ground
exists. (Current draw of the Starter Contactor coil at nominal
voltage is approximately 3.2 amps).
56
TO ECB
0
TO GROUND
Figure 7-18. – Starter Contactor
RESULTS:
1. If continuity is not measured in Step 1, repair or replace Wire
No. 0 between the Starter Contactor and the ground terminal.
2 If engine cranks during Step 2, but would not crank in Test 25,
remove and replace the Starter Contactor.
3. If engine does not crank in this test, go to Test 27.
16
TO STARTER
16
TO ECB
13
TO FUSE (F1)
13
TO BATTERY