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PVM OPTIMUM LOAD CURVE HANDSHAKING
TROUBLESHOOTING
Note: a value of below 0.5VDC or above 9.5VDC (on
circuit 72E to 72R) indicates a failure.
Trucks equipped with DDEC engine:
1. With the engine shut down, keyswitch ON and
control power ON, measure voltage between 72E
(+) and 72R (-) lead. Voltage should be 5.0VDC.
a. If the voltage is low or 0VDC, check voltage of
circuit 15VL @ TB32. (This supply is from the
GE drive system power supply card through
the GE/Auxiliary Control harness.)
Voltage should be 5.0 volts.
b. Then check voltage of circuit 15SIM @ TB32.
Voltage should be approximately 14.5 VDC.
c. If voltage is 0VDC or considerably lower than
14.5 volts, check the 20 ohm resistor on DB1.
2. With the engine running and under load, with
keyswitch and control power switch ON, check
the voltage at 72E(+) to 72R (-).
Voltage should be 5.0 volts
a. If the voltage in step 2 is lower or higher than
5.0 volts, check using the DDR to see the
percent of load the engine is given to the PVM
module.
b. Multiply the percentage value in the previous
step by 10. This should equal the 72E to 72R
voltage reading. (i.e. 50% X 10 = 5.0 VDC)
Note: The DDR is updated every second and is not a
true real (electronic) time value. The GE system up-
dates every 20msec.
A more accurate method of measuring the updated
value is to attach an oscilloscope to the circuit 908M
terminal point to ground and measure the time the
signal is positive divided by the total time of the signal
wave form and multiply it by a factor of 10. This should
equal the 72E to 72R circuit voltage.
This is a 50HZ signal.
Examples:
10ms/20ms = .50 X 10 = 5.0VDC
15ms/20ms = .75 X 10 = 7.5VDC
5ms/20ms = .25 X 10 = 2.5VDC
c. Verify circuit 72R is connected to ground.
d. If the signal "908M" is correct and the supply
voltage (15SIM) to the PVM is correct, but
output is incorrect, replace the PVM module.
E03015 3/01
AC Drive System Electrical Checkout Procedure
(Release 17 Software)
Trucks equipped with Komatsu engine:
1. With the engine shut down, keyswitch ON and
control power ON, measure voltage between 72E
(+) and 72R (-) lead.
Voltage should be 5.0 volts.
a. Jumper circuit 22FO to ground and verify volt-
age on 72E to 72R changes to 7.0VDC.
b. If the voltage is 0VDC, verify the connections to
the PVM are correct and circuit 439 and 11SL
connected to CN P382 positions 5 and 40 are
24VDC.
2. With the engine running and under load, with
keyswitch and control power switch ON, check
the voltage at 72E(+) to 72R (-).
Voltage should be 5.0 volts
a. Check the PVM diagnostic connector P381.
b. Verify the voltage between position A to B is 8
to 11VDC. (A reading of 0VDC indicates the
1939 transmission line line failed. Check 1939
wiring.)
c. Verify the voltage between position C to B is 8
to 11VDC. (A reading of 0VDC indicates the
PVM has failed only if the voltage from position
A to B is correct and the filtering circuit is
correct.)
Check filtering circuit resistors and capacitors
connected to P383 positions 12 and 20 and
P382 position 33 mounted on diode board
DB1.
3. If both step 1 and 2 are 0VDC, then circuit 439 or
11SL or both are incorrect.
Trucks with Either Engine:
If necessary, a variable voltage can be substituted for
the 72E/72R circuit voltage to determine if the problem
is caused by the engine or the GE drive system.
This voltage can be varied above and below 5VDC to
see if the GE drive system follows this signal, dropping
load when the signal is below 5VDC and increasing
load if the signal is above 5VDC.
If the GE drive system follows the signal and with
5VDC the system can produce full power, but cannot
function normally, troubleshoot engine boost or fuel
injection system.
E3-35
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Troubleshooting
